drm/dp: Move DisplayPort helpers into separate helper module

Move DisplayPort functions into a separate module to reduce the size
of the KMS helpers. Select DRM_DP_HELPER for all users of the code. To
avoid naming conflicts, rename drm_dp_helper.c to drm_dp.c

This change can help to reduce the size of the kernel binary. Some
numbers from a x86-64 test build:

Before:
	drm_kms_helper.ko:	447480 bytes

After:
	drm_dp_helper.ko:	216632 bytes
	drm_kms_helper.ko:	239424 bytes

For early-boot graphics, generic DRM drivers, such as simpledrm,
require DRM KMS helpers to be built into the kernel. Generic helper
functions for DisplayPort take up a significant portion of DRM KMS
helper library. These functions are not used by generic drivers and
can be loaded as a module.

v3:
	* fix include statement in DRM selftests
v2:
	* move DP helper code into dp/ (Jani)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Lyude Paul <lyude@redhat.com>
Acked-by: Daniel Vetter <daniel@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220114114535.29157-4-tzimmermann@suse.de

1 files changed, 5977 insertions, 0 deletions

diff --git a/drivers/gpu/drm/dp/drm_dp_mst_topology.c b/drivers/gpu/drm/dp/drm_dp_mst_topology.c
new file mode 100644
index 000000000000..bc3237a09c06
--- /dev/null
+++ b/drivers/gpu/drm/dp/drm_dp_mst_topology.c
@@ -0,0 +1,5977 @@
+/*
+ * Copyright © 2014 Red Hat
+ *
+ * Permission to use, copy, modify, distribute, and sell this software and its
+ * documentation for any purpose is hereby granted without fee, provided that
+ * the above copyright notice appear in all copies and that both that copyright
+ * notice and this permission notice appear in supporting documentation, and
+ * that the name of the copyright holders not be used in advertising or
+ * publicity pertaining to distribution of the software without specific,
+ * written prior permission.  The copyright holders make no representations
+ * about the suitability of this software for any purpose.  It is provided "as
+ * is" without express or implied warranty.
+ *
+ * THE COPYRIGHT HOLDERS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
+ * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
+ * EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY SPECIAL, INDIRECT OR
+ * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
+ * DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
+ * TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
+ * OF THIS SOFTWARE.
+ */
+
+#include <linux/bitfield.h>
+#include <linux/delay.h>
+#include <linux/errno.h>
+#include <linux/i2c.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/random.h>
+#include <linux/sched.h>
+#include <linux/seq_file.h>
+#include <linux/iopoll.h>
+
+#if IS_ENABLED(CONFIG_DRM_DEBUG_DP_MST_TOPOLOGY_REFS)
+#include <linux/stacktrace.h>
+#include <linux/sort.h>
+#include <linux/timekeeping.h>
+#include <linux/math64.h>
+#endif
+
+#include <drm/drm_atomic.h>
+#include <drm/drm_atomic_helper.h>
+#include <drm/drm_dp_mst_helper.h>
+#include <drm/drm_drv.h>
+#include <drm/drm_print.h>
+#include <drm/drm_probe_helper.h>
+
+#include "drm_dp_helper_internal.h"
+#include "drm_dp_mst_topology_internal.h"
+
+/**
+ * DOC: dp mst helper
+ *
+ * These functions contain parts of the DisplayPort 1.2a MultiStream Transport
+ * protocol. The helpers contain a topology manager and bandwidth manager.
+ * The helpers encapsulate the sending and received of sideband msgs.
+ */
+struct drm_dp_pending_up_req {
+	struct drm_dp_sideband_msg_hdr hdr;
+	struct drm_dp_sideband_msg_req_body msg;
+	struct list_head next;
+};
+
+static bool dump_dp_payload_table(struct drm_dp_mst_topology_mgr *mgr,
+				  char *buf);
+
+static void drm_dp_mst_topology_put_port(struct drm_dp_mst_port *port);
+
+static int drm_dp_dpcd_write_payload(struct drm_dp_mst_topology_mgr *mgr,
+				     int id,
+				     struct drm_dp_payload *payload);
+
+static int drm_dp_send_dpcd_read(struct drm_dp_mst_topology_mgr *mgr,
+				 struct drm_dp_mst_port *port,
+				 int offset, int size, u8 *bytes);
+static int drm_dp_send_dpcd_write(struct drm_dp_mst_topology_mgr *mgr,
+				  struct drm_dp_mst_port *port,
+				  int offset, int size, u8 *bytes);
+
+static int drm_dp_send_link_address(struct drm_dp_mst_topology_mgr *mgr,
+				    struct drm_dp_mst_branch *mstb);
+
+static void
+drm_dp_send_clear_payload_id_table(struct drm_dp_mst_topology_mgr *mgr,
+				   struct drm_dp_mst_branch *mstb);
+
+static int drm_dp_send_enum_path_resources(struct drm_dp_mst_topology_mgr *mgr,
+					   struct drm_dp_mst_branch *mstb,
+					   struct drm_dp_mst_port *port);
+static bool drm_dp_validate_guid(struct drm_dp_mst_topology_mgr *mgr,
+				 u8 *guid);
+
+static int drm_dp_mst_register_i2c_bus(struct drm_dp_mst_port *port);
+static void drm_dp_mst_unregister_i2c_bus(struct drm_dp_mst_port *port);
+static void drm_dp_mst_kick_tx(struct drm_dp_mst_topology_mgr *mgr);
+
+static bool drm_dp_mst_port_downstream_of_branch(struct drm_dp_mst_port *port,
+						 struct drm_dp_mst_branch *branch);
+
+#define DBG_PREFIX "[dp_mst]"
+
+#define DP_STR(x) [DP_ ## x] = #x
+
+static const char *drm_dp_mst_req_type_str(u8 req_type)
+{
+	static const char * const req_type_str[] = {
+		DP_STR(GET_MSG_TRANSACTION_VERSION),
+		DP_STR(LINK_ADDRESS),
+		DP_STR(CONNECTION_STATUS_NOTIFY),
+		DP_STR(ENUM_PATH_RESOURCES),
+		DP_STR(ALLOCATE_PAYLOAD),
+		DP_STR(QUERY_PAYLOAD),
+		DP_STR(RESOURCE_STATUS_NOTIFY),
+		DP_STR(CLEAR_PAYLOAD_ID_TABLE),
+		DP_STR(REMOTE_DPCD_READ),
+		DP_STR(REMOTE_DPCD_WRITE),
+		DP_STR(REMOTE_I2C_READ),
+		DP_STR(REMOTE_I2C_WRITE),
+		DP_STR(POWER_UP_PHY),
+		DP_STR(POWER_DOWN_PHY),
+		DP_STR(SINK_EVENT_NOTIFY),
+		DP_STR(QUERY_STREAM_ENC_STATUS),
+	};
+
+	if (req_type >= ARRAY_SIZE(req_type_str) ||
+	    !req_type_str[req_type])
+		return "unknown";
+
+	return req_type_str[req_type];
+}
+
+#undef DP_STR
+#define DP_STR(x) [DP_NAK_ ## x] = #x
+
+static const char *drm_dp_mst_nak_reason_str(u8 nak_reason)
+{
+	static const char * const nak_reason_str[] = {
+		DP_STR(WRITE_FAILURE),
+		DP_STR(INVALID_READ),
+		DP_STR(CRC_FAILURE),
+		DP_STR(BAD_PARAM),
+		DP_STR(DEFER),
+		DP_STR(LINK_FAILURE),
+		DP_STR(NO_RESOURCES),
+		DP_STR(DPCD_FAIL),
+		DP_STR(I2C_NAK),
+		DP_STR(ALLOCATE_FAIL),
+	};
+
+	if (nak_reason >= ARRAY_SIZE(nak_reason_str) ||
+	    !nak_reason_str[nak_reason])
+		return "unknown";
+
+	return nak_reason_str[nak_reason];
+}
+
+#undef DP_STR
+#define DP_STR(x) [DRM_DP_SIDEBAND_TX_ ## x] = #x
+
+static const char *drm_dp_mst_sideband_tx_state_str(int state)
+{
+	static const char * const sideband_reason_str[] = {
+		DP_STR(QUEUED),
+		DP_STR(START_SEND),
+		DP_STR(SENT),
+		DP_STR(RX),
+		DP_STR(TIMEOUT),
+	};
+
+	if (state >= ARRAY_SIZE(sideband_reason_str) ||
+	    !sideband_reason_str[state])
+		return "unknown";
+
+	return sideband_reason_str[state];
+}
+
+static int
+drm_dp_mst_rad_to_str(const u8 rad[8], u8 lct, char *out, size_t len)
+{
+	int i;
+	u8 unpacked_rad[16];
+
+	for (i = 0; i < lct; i++) {
+		if (i % 2)
+			unpacked_rad[i] = rad[i / 2] >> 4;
+		else
+			unpacked_rad[i] = rad[i / 2] & BIT_MASK(4);
+	}
+
+	/* TODO: Eventually add something to printk so we can format the rad
+	 * like this: 1.2.3
+	 */
+	return snprintf(out, len, "%*phC", lct, unpacked_rad);
+}
+
+/* sideband msg handling */
+static u8 drm_dp_msg_header_crc4(const uint8_t *data, size_t num_nibbles)
+{
+	u8 bitmask = 0x80;
+	u8 bitshift = 7;
+	u8 array_index = 0;
+	int number_of_bits = num_nibbles * 4;
+	u8 remainder = 0;
+
+	while (number_of_bits != 0) {
+		number_of_bits--;
+		remainder <<= 1;
+		remainder |= (data[array_index] & bitmask) >> bitshift;
+		bitmask >>= 1;
+		bitshift--;
+		if (bitmask == 0) {
+			bitmask = 0x80;
+			bitshift = 7;
+			array_index++;
+		}
+		if ((remainder & 0x10) == 0x10)
+			remainder ^= 0x13;
+	}
+
+	number_of_bits = 4;
+	while (number_of_bits != 0) {
+		number_of_bits--;
+		remainder <<= 1;
+		if ((remainder & 0x10) != 0)
+			remainder ^= 0x13;
+	}
+
+	return remainder;
+}
+
+static u8 drm_dp_msg_data_crc4(const uint8_t *data, u8 number_of_bytes)
+{
+	u8 bitmask = 0x80;
+	u8 bitshift = 7;
+	u8 array_index = 0;
+	int number_of_bits = number_of_bytes * 8;
+	u16 remainder = 0;
+
+	while (number_of_bits != 0) {
+		number_of_bits--;
+		remainder <<= 1;
+		remainder |= (data[array_index] & bitmask) >> bitshift;
+		bitmask >>= 1;
+		bitshift--;
+		if (bitmask == 0) {
+			bitmask = 0x80;
+			bitshift = 7;
+			array_index++;
+		}
+		if ((remainder & 0x100) == 0x100)
+			remainder ^= 0xd5;
+	}
+
+	number_of_bits = 8;
+	while (number_of_bits != 0) {
+		number_of_bits--;
+		remainder <<= 1;
+		if ((remainder & 0x100) != 0)
+			remainder ^= 0xd5;
+	}
+
+	return remainder & 0xff;
+}
+static inline u8 drm_dp_calc_sb_hdr_size(struct drm_dp_sideband_msg_hdr *hdr)
+{
+	u8 size = 3;
+
+	size += (hdr->lct / 2);
+	return size;
+}
+
+static void drm_dp_encode_sideband_msg_hdr(struct drm_dp_sideband_msg_hdr *hdr,
+					   u8 *buf, int *len)
+{
+	int idx = 0;
+	int i;
+	u8 crc4;
+
+	buf[idx++] = ((hdr->lct & 0xf) << 4) | (hdr->lcr & 0xf);
+	for (i = 0; i < (hdr->lct / 2); i++)
+		buf[idx++] = hdr->rad[i];
+	buf[idx++] = (hdr->broadcast << 7) | (hdr->path_msg << 6) |
+		(hdr->msg_len & 0x3f);
+	buf[idx++] = (hdr->somt << 7) | (hdr->eomt << 6) | (hdr->seqno << 4);
+
+	crc4 = drm_dp_msg_header_crc4(buf, (idx * 2) - 1);
+	buf[idx - 1] |= (crc4 & 0xf);
+
+	*len = idx;
+}
+
+static bool drm_dp_decode_sideband_msg_hdr(const struct drm_dp_mst_topology_mgr *mgr,
+					   struct drm_dp_sideband_msg_hdr *hdr,
+					   u8 *buf, int buflen, u8 *hdrlen)
+{
+	u8 crc4;
+	u8 len;
+	int i;
+	u8 idx;
+
+	if (buf[0] == 0)
+		return false;
+	len = 3;
+	len += ((buf[0] & 0xf0) >> 4) / 2;
+	if (len > buflen)
+		return false;
+	crc4 = drm_dp_msg_header_crc4(buf, (len * 2) - 1);
+
+	if ((crc4 & 0xf) != (buf[len - 1] & 0xf)) {
+		drm_dbg_kms(mgr->dev, "crc4 mismatch 0x%x 0x%x\n", crc4, buf[len - 1]);
+		return false;
+	}
+
+	hdr->lct = (buf[0] & 0xf0) >> 4;
+	hdr->lcr = (buf[0] & 0xf);
+	idx = 1;
+	for (i = 0; i < (hdr->lct / 2); i++)
+		hdr->rad[i] = buf[idx++];
+	hdr->broadcast = (buf[idx] >> 7) & 0x1;
+	hdr->path_msg = (buf[idx] >> 6) & 0x1;
+	hdr->msg_len = buf[idx] & 0x3f;
+	idx++;
+	hdr->somt = (buf[idx] >> 7) & 0x1;
+	hdr->eomt = (buf[idx] >> 6) & 0x1;
+	hdr->seqno = (buf[idx] >> 4) & 0x1;
+	idx++;
+	*hdrlen = idx;
+	return true;
+}
+
+void
+drm_dp_encode_sideband_req(const struct drm_dp_sideband_msg_req_body *req,
+			   struct drm_dp_sideband_msg_tx *raw)
+{
+	int idx = 0;
+	int i;
+	u8 *buf = raw->msg;
+
+	buf[idx++] = req->req_type & 0x7f;
+
+	switch (req->req_type) {
+	case DP_ENUM_PATH_RESOURCES:
+	case DP_POWER_DOWN_PHY:
+	case DP_POWER_UP_PHY:
+		buf[idx] = (req->u.port_num.port_number & 0xf) << 4;
+		idx++;
+		break;
+	case DP_ALLOCATE_PAYLOAD:
+		buf[idx] = (req->u.allocate_payload.port_number & 0xf) << 4 |
+			(req->u.allocate_payload.number_sdp_streams & 0xf);
+		idx++;
+		buf[idx] = (req->u.allocate_payload.vcpi & 0x7f);
+		idx++;
+		buf[idx] = (req->u.allocate_payload.pbn >> 8);
+		idx++;
+		buf[idx] = (req->u.allocate_payload.pbn & 0xff);
+		idx++;
+		for (i = 0; i < req->u.allocate_payload.number_sdp_streams / 2; i++) {
+			buf[idx] = ((req->u.allocate_payload.sdp_stream_sink[i * 2] & 0xf) << 4) |
+				(req->u.allocate_payload.sdp_stream_sink[i * 2 + 1] & 0xf);
+			idx++;
+		}
+		if (req->u.allocate_payload.number_sdp_streams & 1) {
+			i = req->u.allocate_payload.number_sdp_streams - 1;
+			buf[idx] = (req->u.allocate_payload.sdp_stream_sink[i] & 0xf) << 4;
+			idx++;
+		}
+		break;
+	case DP_QUERY_PAYLOAD:
+		buf[idx] = (req->u.query_payload.port_number & 0xf) << 4;
+		idx++;
+		buf[idx] = (req->u.query_payload.vcpi & 0x7f);
+		idx++;
+		break;
+	case DP_REMOTE_DPCD_READ:
+		buf[idx] = (req->u.dpcd_read.port_number & 0xf) << 4;
+		buf[idx] |= ((req->u.dpcd_read.dpcd_address & 0xf0000) >> 16) & 0xf;
+		idx++;
+		buf[idx] = (req->u.dpcd_read.dpcd_address & 0xff00) >> 8;
+		idx++;
+		buf[idx] = (req->u.dpcd_read.dpcd_address & 0xff);
+		idx++;
+		buf[idx] = (req->u.dpcd_read.num_bytes);
+		idx++;
+		break;
+
+	case DP_REMOTE_DPCD_WRITE:
+		buf[idx] = (req->u.dpcd_write.port_number & 0xf) << 4;
+		buf[idx] |= ((req->u.dpcd_write.dpcd_address & 0xf0000) >> 16) & 0xf;
+		idx++;
+		buf[idx] = (req->u.dpcd_write.dpcd_address & 0xff00) >> 8;
+		idx++;
+		buf[idx] = (req->u.dpcd_write.dpcd_address & 0xff);
+		idx++;
+		buf[idx] = (req->u.dpcd_write.num_bytes);
+		idx++;
+		memcpy(&buf[idx], req->u.dpcd_write.bytes, req->u.dpcd_write.num_bytes);
+		idx += req->u.dpcd_write.num_bytes;
+		break;
+	case DP_REMOTE_I2C_READ:
+		buf[idx] = (req->u.i2c_read.port_number & 0xf) << 4;
+		buf[idx] |= (req->u.i2c_read.num_transactions & 0x3);
+		idx++;
+		for (i = 0; i < (req->u.i2c_read.num_transactions & 0x3); i++) {
+			buf[idx] = req->u.i2c_read.transactions[i].i2c_dev_id & 0x7f;
+			idx++;
+			buf[idx] = req->u.i2c_read.transactions[i].num_bytes;
+			idx++;
+			memcpy(&buf[idx], req->u.i2c_read.transactions[i].bytes, req->u.i2c_read.transactions[i].num_bytes);
+			idx += req->u.i2c_read.transactions[i].num_bytes;
+
+			buf[idx] = (req->u.i2c_read.transactions[i].no_stop_bit & 0x1) << 4;
+			buf[idx] |= (req->u.i2c_read.transactions[i].i2c_transaction_delay & 0xf);
+			idx++;
+		}
+		buf[idx] = (req->u.i2c_read.read_i2c_device_id) & 0x7f;
+		idx++;
+		buf[idx] = (req->u.i2c_read.num_bytes_read);
+		idx++;
+		break;
+
+	case DP_REMOTE_I2C_WRITE:
+		buf[idx] = (req->u.i2c_write.port_number & 0xf) << 4;
+		idx++;
+		buf[idx] = (req->u.i2c_write.write_i2c_device_id) & 0x7f;
+		idx++;
+		buf[idx] = (req->u.i2c_write.num_bytes);
+		idx++;
+		memcpy(&buf[idx], req->u.i2c_write.bytes, req->u.i2c_write.num_bytes);
+		idx += req->u.i2c_write.num_bytes;
+		break;
+	case DP_QUERY_STREAM_ENC_STATUS: {
+		const struct drm_dp_query_stream_enc_status *msg;
+
+		msg = &req->u.enc_status;
+		buf[idx] = msg->stream_id;
+		idx++;
+		memcpy(&buf[idx], msg->client_id, sizeof(msg->client_id));
+		idx += sizeof(msg->client_id);
+		buf[idx] = 0;
+		buf[idx] |= FIELD_PREP(GENMASK(1, 0), msg->stream_event);
+		buf[idx] |= msg->valid_stream_event ? BIT(2) : 0;
+		buf[idx] |= FIELD_PREP(GENMASK(4, 3), msg->stream_behavior);
+		buf[idx] |= msg->valid_stream_behavior ? BIT(5) : 0;
+		idx++;
+		}
+		break;
+	}
+	raw->cur_len = idx;
+}
+EXPORT_SYMBOL_FOR_TESTS_ONLY(drm_dp_encode_sideband_req);
+
+/* Decode a sideband request we've encoded, mainly used for debugging */
+int
+drm_dp_decode_sideband_req(const struct drm_dp_sideband_msg_tx *raw,
+			   struct drm_dp_sideband_msg_req_body *req)
+{
+	const u8 *buf = raw->msg;
+	int i, idx = 0;
+
+	req->req_type = buf[idx++] & 0x7f;
+	switch (req->req_type) {
+	case DP_ENUM_PATH_RESOURCES:
+	case DP_POWER_DOWN_PHY:
+	case DP_POWER_UP_PHY:
+		req->u.port_num.port_number = (buf[idx] >> 4) & 0xf;
+		break;
+	case DP_ALLOCATE_PAYLOAD:
+		{
+			struct drm_dp_allocate_payload *a =
+				&req->u.allocate_payload;
+
+			a->number_sdp_streams = buf[idx] & 0xf;
+			a->port_number = (buf[idx] >> 4) & 0xf;
+
+			WARN_ON(buf[++idx] & 0x80);
+			a->vcpi = buf[idx] & 0x7f;
+
+			a->pbn = buf[++idx] << 8;
+			a->pbn |= buf[++idx];
+
+			idx++;
+			for (i = 0; i < a->number_sdp_streams; i++) {
+				a->sdp_stream_sink[i] =
+					(buf[idx + (i / 2)] >> ((i % 2) ? 0 : 4)) & 0xf;
+			}
+		}
+		break;
+	case DP_QUERY_PAYLOAD:
+		req->u.query_payload.port_number = (buf[idx] >> 4) & 0xf;
+		WARN_ON(buf[++idx] & 0x80);
+		req->u.query_payload.vcpi = buf[idx] & 0x7f;
+		break;
+	case DP_REMOTE_DPCD_READ:
+		{
+			struct drm_dp_remote_dpcd_read *r = &req->u.dpcd_read;
+
+			r->port_number = (buf[idx] >> 4) & 0xf;
+
+			r->dpcd_address = (buf[idx] << 16) & 0xf0000;
+			r->dpcd_address |= (buf[++idx] << 8) & 0xff00;
+			r->dpcd_address |= buf[++idx] & 0xff;
+
+			r->num_bytes = buf[++idx];
+		}
+		break;
+	case DP_REMOTE_DPCD_WRITE:
+		{
+			struct drm_dp_remote_dpcd_write *w =
+				&req->u.dpcd_write;
+
+			w->port_number = (buf[idx] >> 4) & 0xf;
+
+			w->dpcd_address = (buf[idx] << 16) & 0xf0000;
+			w->dpcd_address |= (buf[++idx] << 8) & 0xff00;
+			w->dpcd_address |= buf[++idx] & 0xff;
+
+			w->num_bytes = buf[++idx];
+
+			w->bytes = kmemdup(&buf[++idx], w->num_bytes,
+					   GFP_KERNEL);
+			if (!w->bytes)
+				return -ENOMEM;
+		}
+		break;
+	case DP_REMOTE_I2C_READ:
+		{
+			struct drm_dp_remote_i2c_read *r = &req->u.i2c_read;
+			struct drm_dp_remote_i2c_read_tx *tx;
+			bool failed = false;
+
+			r->num_transactions = buf[idx] & 0x3;
+			r->port_number = (buf[idx] >> 4) & 0xf;
+			for (i = 0; i < r->num_transactions; i++) {
+				tx = &r->transactions[i];
+
+				tx->i2c_dev_id = buf[++idx] & 0x7f;
+				tx->num_bytes = buf[++idx];
+				tx->bytes = kmemdup(&buf[++idx],
+						    tx->num_bytes,
+						    GFP_KERNEL);
+				if (!tx->bytes) {
+					failed = true;
+					break;
+				}
+				idx += tx->num_bytes;
+				tx->no_stop_bit = (buf[idx] >> 5) & 0x1;
+				tx->i2c_transaction_delay = buf[idx] & 0xf;
+			}
+
+			if (failed) {
+				for (i = 0; i < r->num_transactions; i++) {
+					tx = &r->transactions[i];
+					kfree(tx->bytes);
+				}
+				return -ENOMEM;
+			}
+
+			r->read_i2c_device_id = buf[++idx] & 0x7f;
+			r->num_bytes_read = buf[++idx];
+		}
+		break;
+	case DP_REMOTE_I2C_WRITE:
+		{
+			struct drm_dp_remote_i2c_write *w = &req->u.i2c_write;
+
+			w->port_number = (buf[idx] >> 4) & 0xf;
+			w->write_i2c_device_id = buf[++idx] & 0x7f;
+			w->num_bytes = buf[++idx];
+			w->bytes = kmemdup(&buf[++idx], w->num_bytes,
+					   GFP_KERNEL);
+			if (!w->bytes)
+				return -ENOMEM;
+		}
+		break;
+	case DP_QUERY_STREAM_ENC_STATUS:
+		req->u.enc_status.stream_id = buf[idx++];
+		for (i = 0; i < sizeof(req->u.enc_status.client_id); i++)
+			req->u.enc_status.client_id[i] = buf[idx++];
+
+		req->u.enc_status.stream_event = FIELD_GET(GENMASK(1, 0),
+							   buf[idx]);
+		req->u.enc_status.valid_stream_event = FIELD_GET(BIT(2),
+								 buf[idx]);
+		req->u.enc_status.stream_behavior = FIELD_GET(GENMASK(4, 3),
+							      buf[idx]);
+		req->u.enc_status.valid_stream_behavior = FIELD_GET(BIT(5),
+								    buf[idx]);
+		break;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_FOR_TESTS_ONLY(drm_dp_decode_sideband_req);
+
+void
+drm_dp_dump_sideband_msg_req_body(const struct drm_dp_sideband_msg_req_body *req,
+				  int indent, struct drm_printer *printer)
+{
+	int i;
+
+#define P(f, ...) drm_printf_indent(printer, indent, f, ##__VA_ARGS__)
+	if (req->req_type == DP_LINK_ADDRESS) {
+		/* No contents to print */
+		P("type=%s\n", drm_dp_mst_req_type_str(req->req_type));
+		return;
+	}
+
+	P("type=%s contents:\n", drm_dp_mst_req_type_str(req->req_type));
+	indent++;
+
+	switch (req->req_type) {
+	case DP_ENUM_PATH_RESOURCES:
+	case DP_POWER_DOWN_PHY:
+	case DP_POWER_UP_PHY:
+		P("port=%d\n", req->u.port_num.port_number);
+		break;
+	case DP_ALLOCATE_PAYLOAD:
+		P("port=%d vcpi=%d pbn=%d sdp_streams=%d %*ph\n",
+		  req->u.allocate_payload.port_number,
+		  req->u.allocate_payload.vcpi, req->u.allocate_payload.pbn,
+		  req->u.allocate_payload.number_sdp_streams,
+		  req->u.allocate_payload.number_sdp_streams,
+		  req->u.allocate_payload.sdp_stream_sink);
+		break;
+	case DP_QUERY_PAYLOAD:
+		P("port=%d vcpi=%d\n",
+		  req->u.query_payload.port_number,
+		  req->u.query_payload.vcpi);
+		break;
+	case DP_REMOTE_DPCD_READ:
+		P("port=%d dpcd_addr=%05x len=%d\n",
+		  req->u.dpcd_read.port_number, req->u.dpcd_read.dpcd_address,
+		  req->u.dpcd_read.num_bytes);
+		break;
+	case DP_REMOTE_DPCD_WRITE:
+		P("port=%d addr=%05x len=%d: %*ph\n",
+		  req->u.dpcd_write.port_number,
+		  req->u.dpcd_write.dpcd_address,
+		  req->u.dpcd_write.num_bytes, req->u.dpcd_write.num_bytes,
+		  req->u.dpcd_write.bytes);
+		break;
+	case DP_REMOTE_I2C_READ:
+		P("port=%d num_tx=%d id=%d size=%d:\n",
+		  req->u.i2c_read.port_number,
+		  req->u.i2c_read.num_transactions,
+		  req->u.i2c_read.read_i2c_device_id,
+		  req->u.i2c_read.num_bytes_read);
+
+		indent++;
+		for (i = 0; i < req->u.i2c_read.num_transactions; i++) {
+			const struct drm_dp_remote_i2c_read_tx *rtx =
+				&req->u.i2c_read.transactions[i];
+
+			P("%d: id=%03d size=%03d no_stop_bit=%d tx_delay=%03d: %*ph\n",
+			  i, rtx->i2c_dev_id, rtx->num_bytes,
+			  rtx->no_stop_bit, rtx->i2c_transaction_delay,
+			  rtx->num_bytes, rtx->bytes);
+		}
+		break;
+	case DP_REMOTE_I2C_WRITE:
+		P("port=%d id=%d size=%d: %*ph\n",
+		  req->u.i2c_write.port_number,
+		  req->u.i2c_write.write_i2c_device_id,
+		  req->u.i2c_write.num_bytes, req->u.i2c_write.num_bytes,
+		  req->u.i2c_write.bytes);
+		break;
+	case DP_QUERY_STREAM_ENC_STATUS:
+		P("stream_id=%u client_id=%*ph stream_event=%x "
+		  "valid_event=%d stream_behavior=%x valid_behavior=%d",
+		  req->u.enc_status.stream_id,
+		  (int)ARRAY_SIZE(req->u.enc_status.client_id),
+		  req->u.enc_status.client_id, req->u.enc_status.stream_event,
+		  req->u.enc_status.valid_stream_event,
+		  req->u.enc_status.stream_behavior,
+		  req->u.enc_status.valid_stream_behavior);
+		break;
+	default:
+		P("???\n");
+		break;
+	}
+#undef P
+}
+EXPORT_SYMBOL_FOR_TESTS_ONLY(drm_dp_dump_sideband_msg_req_body);
+
+static inline void
+drm_dp_mst_dump_sideband_msg_tx(struct drm_printer *p,
+				const struct drm_dp_sideband_msg_tx *txmsg)
+{
+	struct drm_dp_sideband_msg_req_body req;
+	char buf[64];
+	int ret;
+	int i;
+
+	drm_dp_mst_rad_to_str(txmsg->dst->rad, txmsg->dst->lct, buf,
+			      sizeof(buf));
+	drm_printf(p, "txmsg cur_offset=%x cur_len=%x seqno=%x state=%s path_msg=%d dst=%s\n",
+		   txmsg->cur_offset, txmsg->cur_len, txmsg->seqno,
+		   drm_dp_mst_sideband_tx_state_str(txmsg->state),
+		   txmsg->path_msg, buf);
+
+	ret = drm_dp_decode_sideband_req(txmsg, &req);
+	if (ret) {
+		drm_printf(p, "<failed to decode sideband req: %d>\n", ret);
+		return;
+	}
+	drm_dp_dump_sideband_msg_req_body(&req, 1, p);
+
+	switch (req.req_type) {
+	case DP_REMOTE_DPCD_WRITE:
+		kfree(req.u.dpcd_write.bytes);
+		break;
+	case DP_REMOTE_I2C_READ:
+		for (i = 0; i < req.u.i2c_read.num_transactions; i++)
+			kfree(req.u.i2c_read.transactions[i].bytes);
+		break;
+	case DP_REMOTE_I2C_WRITE:
+		kfree(req.u.i2c_write.bytes);
+		break;
+	}
+}
+
+static void drm_dp_crc_sideband_chunk_req(u8 *msg, u8 len)
+{
+	u8 crc4;
+
+	crc4 = drm_dp_msg_data_crc4(msg, len);
+	msg[len] = crc4;
+}
+
+static void drm_dp_encode_sideband_reply(struct drm_dp_sideband_msg_reply_body *rep,
+					 struct drm_dp_sideband_msg_tx *raw)
+{
+	int idx = 0;
+	u8 *buf = raw->msg;
+
+	buf[idx++] = (rep->reply_type & 0x1) << 7 | (rep->req_type & 0x7f);
+
+	raw->cur_len = idx;
+}
+
+static int drm_dp_sideband_msg_set_header(struct drm_dp_sideband_msg_rx *msg,
+					  struct drm_dp_sideband_msg_hdr *hdr,
+					  u8 hdrlen)
+{
+	/*
+	 * ignore out-of-order messages or messages that are part of a
+	 * failed transaction
+	 */
+	if (!hdr->somt && !msg->have_somt)
+		return false;
+
+	/* get length contained in this portion */
+	msg->curchunk_idx = 0;
+	msg->curchunk_len = hdr->msg_len;
+	msg->curchunk_hdrlen = hdrlen;
+
+	/* we have already gotten an somt - don't bother parsing */
+	if (hdr->somt && msg->have_somt)
+		return false;
+
+	if (hdr->somt) {
+		memcpy(&msg->initial_hdr, hdr,
+		       sizeof(struct drm_dp_sideband_msg_hdr));
+		msg->have_somt = true;
+	}
+	if (hdr->eomt)
+		msg->have_eomt = true;
+
+	return true;
+}
+
+/* this adds a chunk of msg to the builder to get the final msg */
+static bool drm_dp_sideband_append_payload(struct drm_dp_sideband_msg_rx *msg,
+					   u8 *replybuf, u8 replybuflen)
+{
+	u8 crc4;
+
+	memcpy(&msg->chunk[msg->curchunk_idx], replybuf, replybuflen);
+	msg->curchunk_idx += replybuflen;
+
+	if (msg->curchunk_idx >= msg->curchunk_len) {
+		/* do CRC */
+		crc4 = drm_dp_msg_data_crc4(msg->chunk, msg->curchunk_len - 1);
+		if (crc4 != msg->chunk[msg->curchunk_len - 1])
+			print_hex_dump(KERN_DEBUG, "wrong crc",
+				       DUMP_PREFIX_NONE, 16, 1,
+				       msg->chunk,  msg->curchunk_len, false);
+		/* copy chunk into bigger msg */
+		memcpy(&msg->msg[msg->curlen], msg->chunk, msg->curchunk_len - 1);
+		msg->curlen += msg->curchunk_len - 1;
+	}
+	return true;
+}
+
+static bool drm_dp_sideband_parse_link_address(const struct drm_dp_mst_topology_mgr *mgr,
+					       struct drm_dp_sideband_msg_rx *raw,
+					       struct drm_dp_sideband_msg_reply_body *repmsg)
+{
+	int idx = 1;
+	int i;
+
+	memcpy(repmsg->u.link_addr.guid, &raw->msg[idx], 16);
+	idx += 16;
+	repmsg->u.link_addr.nports = raw->msg[idx] & 0xf;
+	idx++;
+	if (idx > raw->curlen)
+		goto fail_len;
+	for (i = 0; i < repmsg->u.link_addr.nports; i++) {
+		if (raw->msg[idx] & 0x80)
+			repmsg->u.link_addr.ports[i].input_port = 1;
+
+		repmsg->u.link_addr.ports[i].peer_device_type = (raw->msg[idx] >> 4) & 0x7;
+		repmsg->u.link_addr.ports[i].port_number = (raw->msg[idx] & 0xf);
+
+		idx++;
+		if (idx > raw->curlen)
+			goto fail_len;
+		repmsg->u.link_addr.ports[i].mcs = (raw->msg[idx] >> 7) & 0x1;
+		repmsg->u.link_addr.ports[i].ddps = (raw->msg[idx] >> 6) & 0x1;
+		if (repmsg->u.link_addr.ports[i].input_port == 0)
+			repmsg->u.link_addr.ports[i].legacy_device_plug_status = (raw->msg[idx] >> 5) & 0x1;
+		idx++;
+		if (idx > raw->curlen)
+			goto fail_len;
+		if (repmsg->u.link_addr.ports[i].input_port == 0) {
+			repmsg->u.link_addr.ports[i].dpcd_revision = (raw->msg[idx]);
+			idx++;
+			if (idx > raw->curlen)
+				goto fail_len;
+			memcpy(repmsg->u.link_addr.ports[i].peer_guid, &raw->msg[idx], 16);
+			idx += 16;
+			if (idx > raw->curlen)
+				goto fail_len;
+			repmsg->u.link_addr.ports[i].num_sdp_streams = (raw->msg[idx] >> 4) & 0xf;
+			repmsg->u.link_addr.ports[i].num_sdp_stream_sinks = (raw->msg[idx] & 0xf);
+			idx++;
+
+		}
+		if (idx > raw->curlen)
+			goto fail_len;
+	}
+
+	return true;
+fail_len:
+	DRM_DEBUG_KMS("link address reply parse length fail %d %d\n", idx, raw->curlen);
+	return false;
+}
+
+static bool drm_dp_sideband_parse_remote_dpcd_read(struct drm_dp_sideband_msg_rx *raw,
+						   struct drm_dp_sideband_msg_reply_body *repmsg)
+{
+	int idx = 1;
+
+	repmsg->u.remote_dpcd_read_ack.port_number = raw->msg[idx] & 0xf;
+	idx++;
+	if (idx > raw->curlen)
+		goto fail_len;
+	repmsg->u.remote_dpcd_read_ack.num_bytes = raw->msg[idx];
+	idx++;
+	if (idx > raw->curlen)
+		goto fail_len;
+
+	memcpy(repmsg->u.remote_dpcd_read_ack.bytes, &raw->msg[idx], repmsg->u.remote_dpcd_read_ack.num_bytes);
+	return true;
+fail_len:
+	DRM_DEBUG_KMS("link address reply parse length fail %d %d\n", idx, raw->curlen);
+	return false;
+}
+
+static bool drm_dp_sideband_parse_remote_dpcd_write(struct drm_dp_sideband_msg_rx *raw,
+						      struct drm_dp_sideband_msg_reply_body *repmsg)
+{
+	int idx = 1;
+
+	repmsg->u.remote_dpcd_write_ack.port_number = raw->msg[idx] & 0xf;
+	idx++;
+	if (idx > raw->curlen)
+		goto fail_len;
+	return true;
+fail_len:
+	DRM_DEBUG_KMS("parse length fail %d %d\n", idx, raw->curlen);
+	return false;
+}
+
+static bool drm_dp_sideband_parse_remote_i2c_read_ack(struct drm_dp_sideband_msg_rx *raw,
+						      struct drm_dp_sideband_msg_reply_body *repmsg)
+{
+	int idx = 1;
+
+	repmsg->u.remote_i2c_read_ack.port_number = (raw->msg[idx] & 0xf);
+	idx++;
+	if (idx > raw->curlen)
+		goto fail_len;
+	repmsg->u.remote_i2c_read_ack.num_bytes = raw->msg[idx];
+	idx++;
+	/* TODO check */
+	memcpy(repmsg->u.remote_i2c_read_ack.bytes, &raw->msg[idx], repmsg->u.remote_i2c_read_ack.num_bytes);
+	return true;
+fail_len:
+	DRM_DEBUG_KMS("remote i2c reply parse length fail %d %d\n", idx, raw->curlen);
+	return false;
+}
+
+static bool drm_dp_sideband_parse_enum_path_resources_ack(struct drm_dp_sideband_msg_rx *raw,
+							  struct drm_dp_sideband_msg_reply_body *repmsg)
+{
+	int idx = 1;
+
+	repmsg->u.path_resources.port_number = (raw->msg[idx] >> 4) & 0xf;
+	repmsg->u.path_resources.fec_capable = raw->msg[idx] & 0x1;
+	idx++;
+	if (idx > raw->curlen)
+		goto fail_len;
+	repmsg->u.path_resources.full_payload_bw_number = (raw->msg[idx] << 8) | (raw->msg[idx+1]);
+	idx += 2;
+	if (idx > raw->curlen)
+		goto fail_len;
+	repmsg->u.path_resources.avail_payload_bw_number = (raw->msg[idx] << 8) | (raw->msg[idx+1]);
+	idx += 2;
+	if (idx > raw->curlen)
+		goto fail_len;
+	return true;
+fail_len:
+	DRM_DEBUG_KMS("enum resource parse length fail %d %d\n", idx, raw->curlen);
+	return false;
+}
+
+static bool drm_dp_sideband_parse_allocate_payload_ack(struct drm_dp_sideband_msg_rx *raw,
+							  struct drm_dp_sideband_msg_reply_body *repmsg)
+{
+	int idx = 1;
+
+	repmsg->u.allocate_payload.port_number = (raw->msg[idx] >> 4) & 0xf;
+	idx++;
+	if (idx > raw->curlen)
+		goto fail_len;
+	repmsg->u.allocate_payload.vcpi = raw->msg[idx];
+	idx++;
+	if (idx > raw->curlen)
+		goto fail_len;
+	repmsg->u.allocate_payload.allocated_pbn = (raw->msg[idx] << 8) | (raw->msg[idx+1]);
+	idx += 2;
+	if (idx > raw->curlen)
+		goto fail_len;
+	return true;
+fail_len:
+	DRM_DEBUG_KMS("allocate payload parse length fail %d %d\n", idx, raw->curlen);
+	return false;
+}
+
+static bool drm_dp_sideband_parse_query_payload_ack(struct drm_dp_sideband_msg_rx *raw,
+						    struct drm_dp_sideband_msg_reply_body *repmsg)
+{
+	int idx = 1;
+
+	repmsg->u.query_payload.port_number = (raw->msg[idx] >> 4) & 0xf;
+	idx++;
+	if (idx > raw->curlen)
+		goto fail_len;
+	repmsg->u.query_payload.allocated_pbn = (raw->msg[idx] << 8) | (raw->msg[idx + 1]);
+	idx += 2;
+	if (idx > raw->curlen)
+		goto fail_len;
+	return true;
+fail_len:
+	DRM_DEBUG_KMS("query payload parse length fail %d %d\n", idx, raw->curlen);
+	return false;
+}
+
+static bool drm_dp_sideband_parse_power_updown_phy_ack(struct drm_dp_sideband_msg_rx *raw,
+						       struct drm_dp_sideband_msg_reply_body *repmsg)
+{
+	int idx = 1;
+
+	repmsg->u.port_number.port_number = (raw->msg[idx] >> 4) & 0xf;
+	idx++;
+	if (idx > raw->curlen) {
+		DRM_DEBUG_KMS("power up/down phy parse length fail %d %d\n",
+			      idx, raw->curlen);
+		return false;
+	}
+	return true;
+}
+
+static bool
+drm_dp_sideband_parse_query_stream_enc_status(
+				struct drm_dp_sideband_msg_rx *raw,
+				struct drm_dp_sideband_msg_reply_body *repmsg)
+{
+	struct drm_dp_query_stream_enc_status_ack_reply *reply;
+
+	reply = &repmsg->u.enc_status;
+
+	reply->stream_id = raw->msg[3];
+
+	reply->reply_signed = raw->msg[2] & BIT(0);
+
+	/*
+	 * NOTE: It's my impression from reading the spec that the below parsing
+	 * is correct. However I noticed while testing with an HDCP 1.4 display
+	 * through an HDCP 2.2 hub that only bit 3 was set. In that case, I
+	 * would expect both bits to be set. So keep the parsing following the
+	 * spec, but beware reality might not match the spec (at least for some
+	 * configurations).
+	 */
+	reply->hdcp_1x_device_present = raw->msg[2] & BIT(4);
+	reply->hdcp_2x_device_present = raw->msg[2] & BIT(3);
+
+	reply->query_capable_device_present = raw->msg[2] & BIT(5);
+	reply->legacy_device_present = raw->msg[2] & BIT(6);
+	reply->unauthorizable_device_present = raw->msg[2] & BIT(7);
+
+	reply->auth_completed = !!(raw->msg[1] & BIT(3));
+	reply->encryption_enabled = !!(raw->msg[1] & BIT(4));
+	reply->repeater_present = !!(raw->msg[1] & BIT(5));
+	reply->state = (raw->msg[1] & GENMASK(7, 6)) >> 6;
+
+	return true;
+}
+
+static bool drm_dp_sideband_parse_reply(const struct drm_dp_mst_topology_mgr *mgr,
+					struct drm_dp_sideband_msg_rx *raw,
+					struct drm_dp_sideband_msg_reply_body *msg)
+{
+	memset(msg, 0, sizeof(*msg));
+	msg->reply_type = (raw->msg[0] & 0x80) >> 7;
+	msg->req_type = (raw->msg[0] & 0x7f);
+
+	if (msg->reply_type == DP_SIDEBAND_REPLY_NAK) {
+		memcpy(msg->u.nak.guid, &raw->msg[1], 16);
+		msg->u.nak.reason = raw->msg[17];
+		msg->u.nak.nak_data = raw->msg[18];
+		return false;
+	}
+
+	switch (msg->req_type) {
+	case DP_LINK_ADDRESS:
+		return drm_dp_sideband_parse_link_address(mgr, raw, msg);
+	case DP_QUERY_PAYLOAD:
+		return drm_dp_sideband_parse_query_payload_ack(raw, msg);
+	case DP_REMOTE_DPCD_READ:
+		return drm_dp_sideband_parse_remote_dpcd_read(raw, msg);
+	case DP_REMOTE_DPCD_WRITE:
+		return drm_dp_sideband_parse_remote_dpcd_write(raw, msg);
+	case DP_REMOTE_I2C_READ:
+		return drm_dp_sideband_parse_remote_i2c_read_ack(raw, msg);
+	case DP_REMOTE_I2C_WRITE:
+		return true; /* since there's nothing to parse */
+	case DP_ENUM_PATH_RESOURCES:
+		return drm_dp_sideband_parse_enum_path_resources_ack(raw, msg);
+	case DP_ALLOCATE_PAYLOAD:
+		return drm_dp_sideband_parse_allocate_payload_ack(raw, msg);
+	case DP_POWER_DOWN_PHY:
+	case DP_POWER_UP_PHY:
+		return drm_dp_sideband_parse_power_updown_phy_ack(raw, msg);
+	case DP_CLEAR_PAYLOAD_ID_TABLE:
+		return true; /* since there's nothing to parse */
+	case DP_QUERY_STREAM_ENC_STATUS:
+		return drm_dp_sideband_parse_query_stream_enc_status(raw, msg);
+	default:
+		drm_err(mgr->dev, "Got unknown reply 0x%02x (%s)\n",
+			msg->req_type, drm_dp_mst_req_type_str(msg->req_type));
+		return false;
+	}
+}
+
+static bool
+drm_dp_sideband_parse_connection_status_notify(const struct drm_dp_mst_topology_mgr *mgr,
+					       struct drm_dp_sideband_msg_rx *raw,
+					       struct drm_dp_sideband_msg_req_body *msg)
+{
+	int idx = 1;
+
+	msg->u.conn_stat.port_number = (raw->msg[idx] & 0xf0) >> 4;
+	idx++;
+	if (idx > raw->curlen)
+		goto fail_len;
+
+	memcpy(msg->u.conn_stat.guid, &raw->msg[idx], 16);
+	idx += 16;
+	if (idx > raw->curlen)
+		goto fail_len;
+
+	msg->u.conn_stat.legacy_device_plug_status = (raw->msg[idx] >> 6) & 0x1;
+	msg->u.conn_stat.displayport_device_plug_status = (raw->msg[idx] >> 5) & 0x1;
+	msg->u.conn_stat.message_capability_status = (raw->msg[idx] >> 4) & 0x1;
+	msg->u.conn_stat.input_port = (raw->msg[idx] >> 3) & 0x1;
+	msg->u.conn_stat.peer_device_type = (raw->msg[idx] & 0x7);
+	idx++;
+	return true;
+fail_len:
+	drm_dbg_kms(mgr->dev, "connection status reply parse length fail %d %d\n",
+		    idx, raw->curlen);
+	return false;
+}
+
+static bool drm_dp_sideband_parse_resource_status_notify(const struct drm_dp_mst_topology_mgr *mgr,
+							 struct drm_dp_sideband_msg_rx *raw,
+							 struct drm_dp_sideband_msg_req_body *msg)
+{
+	int idx = 1;
+
+	msg->u.resource_stat.port_number = (raw->msg[idx] & 0xf0) >> 4;
+	idx++;
+	if (idx > raw->curlen)
+		goto fail_len;
+
+	memcpy(msg->u.resource_stat.guid, &raw->msg[idx], 16);
+	idx += 16;
+	if (idx > raw->curlen)
+		goto fail_len;
+
+	msg->u.resource_stat.available_pbn = (raw->msg[idx] << 8) | (raw->msg[idx + 1]);
+	idx++;
+	return true;
+fail_len:
+	drm_dbg_kms(mgr->dev, "resource status reply parse length fail %d %d\n", idx, raw->curlen);
+	return false;
+}
+
+static bool drm_dp_sideband_parse_req(const struct drm_dp_mst_topology_mgr *mgr,
+				      struct drm_dp_sideband_msg_rx *raw,
+				      struct drm_dp_sideband_msg_req_body *msg)
+{
+	memset(msg, 0, sizeof(*msg));
+	msg->req_type = (raw->msg[0] & 0x7f);
+
+	switch (msg->req_type) {
+	case DP_CONNECTION_STATUS_NOTIFY:
+		return drm_dp_sideband_parse_connection_status_notify(mgr, raw, msg);
+	case DP_RESOURCE_STATUS_NOTIFY:
+		return drm_dp_sideband_parse_resource_status_notify(mgr, raw, msg);
+	default:
+		drm_err(mgr->dev, "Got unknown request 0x%02x (%s)\n",
+			msg->req_type, drm_dp_mst_req_type_str(msg->req_type));
+		return false;
+	}
+}
+
+static void build_dpcd_write(struct drm_dp_sideband_msg_tx *msg,
+			     u8 port_num, u32 offset, u8 num_bytes, u8 *bytes)
+{
+	struct drm_dp_sideband_msg_req_body req;
+
+	req.req_type = DP_REMOTE_DPCD_WRITE;
+	req.u.dpcd_write.port_number = port_num;
+	req.u.dpcd_write.dpcd_address = offset;
+	req.u.dpcd_write.num_bytes = num_bytes;
+	req.u.dpcd_write.bytes = bytes;
+	drm_dp_encode_sideband_req(&req, msg);
+}
+
+static void build_link_address(struct drm_dp_sideband_msg_tx *msg)
+{
+	struct drm_dp_sideband_msg_req_body req;
+
+	req.req_type = DP_LINK_ADDRESS;
+	drm_dp_encode_sideband_req(&req, msg);
+}
+
+static void build_clear_payload_id_table(struct drm_dp_sideband_msg_tx *msg)
+{
+	struct drm_dp_sideband_msg_req_body req;
+
+	req.req_type = DP_CLEAR_PAYLOAD_ID_TABLE;
+	drm_dp_encode_sideband_req(&req, msg);
+	msg->path_msg = true;
+}
+
+static int build_enum_path_resources(struct drm_dp_sideband_msg_tx *msg,
+				     int port_num)
+{
+	struct drm_dp_sideband_msg_req_body req;
+
+	req.req_type = DP_ENUM_PATH_RESOURCES;
+	req.u.port_num.port_number = port_num;
+	drm_dp_encode_sideband_req(&req, msg);
+	msg->path_msg = true;
+	return 0;
+}
+
+static void build_allocate_payload(struct drm_dp_sideband_msg_tx *msg,
+				   int port_num,
+				   u8 vcpi, uint16_t pbn,
+				   u8 number_sdp_streams,
+				   u8 *sdp_stream_sink)
+{
+	struct drm_dp_sideband_msg_req_body req;
+
+	memset(&req, 0, sizeof(req));
+	req.req_type = DP_ALLOCATE_PAYLOAD;
+	req.u.allocate_payload.port_number = port_num;
+	req.u.allocate_payload.vcpi = vcpi;
+	req.u.allocate_payload.pbn = pbn;
+	req.u.allocate_payload.number_sdp_streams = number_sdp_streams;
+	memcpy(req.u.allocate_payload.sdp_stream_sink, sdp_stream_sink,
+		   number_sdp_streams);
+	drm_dp_encode_sideband_req(&req, msg);
+	msg->path_msg = true;
+}
+
+static void build_power_updown_phy(struct drm_dp_sideband_msg_tx *msg,
+				   int port_num, bool power_up)
+{
+	struct drm_dp_sideband_msg_req_body req;
+
+	if (power_up)
+		req.req_type = DP_POWER_UP_PHY;
+	else
+		req.req_type = DP_POWER_DOWN_PHY;
+
+	req.u.port_num.port_number = port_num;
+	drm_dp_encode_sideband_req(&req, msg);
+	msg->path_msg = true;
+}
+
+static int
+build_query_stream_enc_status(struct drm_dp_sideband_msg_tx *msg, u8 stream_id,
+			      u8 *q_id)
+{
+	struct drm_dp_sideband_msg_req_body req;
+
+	req.req_type = DP_QUERY_STREAM_ENC_STATUS;
+	req.u.enc_status.stream_id = stream_id;
+	memcpy(req.u.enc_status.client_id, q_id,
+	       sizeof(req.u.enc_status.client_id));
+	req.u.enc_status.stream_event = 0;
+	req.u.enc_status.valid_stream_event = false;
+	req.u.enc_status.stream_behavior = 0;
+	req.u.enc_status.valid_stream_behavior = false;
+
+	drm_dp_encode_sideband_req(&req, msg);
+	return 0;
+}
+
+static int drm_dp_mst_assign_payload_id(struct drm_dp_mst_topology_mgr *mgr,
+					struct drm_dp_vcpi *vcpi)
+{
+	int ret, vcpi_ret;
+
+	mutex_lock(&mgr->payload_lock);
+	ret = find_first_zero_bit(&mgr->payload_mask, mgr->max_payloads + 1);
+	if (ret > mgr->max_payloads) {
+		ret = -EINVAL;
+		drm_dbg_kms(mgr->dev, "out of payload ids %d\n", ret);
+		goto out_unlock;
+	}
+
+	vcpi_ret = find_first_zero_bit(&mgr->vcpi_mask, mgr->max_payloads + 1);
+	if (vcpi_ret > mgr->max_payloads) {
+		ret = -EINVAL;
+		drm_dbg_kms(mgr->dev, "out of vcpi ids %d\n", ret);
+		goto out_unlock;
+	}
+
+	set_bit(ret, &mgr->payload_mask);
+	set_bit(vcpi_ret, &mgr->vcpi_mask);
+	vcpi->vcpi = vcpi_ret + 1;
+	mgr->proposed_vcpis[ret - 1] = vcpi;
+out_unlock:
+	mutex_unlock(&mgr->payload_lock);
+	return ret;
+}
+
+static void drm_dp_mst_put_payload_id(struct drm_dp_mst_topology_mgr *mgr,
+				      int vcpi)
+{
+	int i;
+
+	if (vcpi == 0)
+		return;
+
+	mutex_lock(&mgr->payload_lock);
+	drm_dbg_kms(mgr->dev, "putting payload %d\n", vcpi);
+	clear_bit(vcpi - 1, &mgr->vcpi_mask);
+
+	for (i = 0; i < mgr->max_payloads; i++) {
+		if (mgr->proposed_vcpis[i] &&
+		    mgr->proposed_vcpis[i]->vcpi == vcpi) {
+			mgr->proposed_vcpis[i] = NULL;
+			clear_bit(i + 1, &mgr->payload_mask);
+		}
+	}
+	mutex_unlock(&mgr->payload_lock);
+}
+
+static bool check_txmsg_state(struct drm_dp_mst_topology_mgr *mgr,
+			      struct drm_dp_sideband_msg_tx *txmsg)
+{
+	unsigned int state;
+
+	/*
+	 * All updates to txmsg->state are protected by mgr->qlock, and the two
+	 * cases we check here are terminal states. For those the barriers
+	 * provided by the wake_up/wait_event pair are enough.
+	 */
+	state = READ_ONCE(txmsg->state);
+	return (state == DRM_DP_SIDEBAND_TX_RX ||
+		state == DRM_DP_SIDEBAND_TX_TIMEOUT);
+}
+
+static int drm_dp_mst_wait_tx_reply(struct drm_dp_mst_branch *mstb,
+				    struct drm_dp_sideband_msg_tx *txmsg)
+{
+	struct drm_dp_mst_topology_mgr *mgr = mstb->mgr;
+	unsigned long wait_timeout = msecs_to_jiffies(4000);
+	unsigned long wait_expires = jiffies + wait_timeout;
+	int ret;
+
+	for (;;) {
+		/*
+		 * If the driver provides a way for this, change to
+		 * poll-waiting for the MST reply interrupt if we didn't receive
+		 * it for 50 msec. This would cater for cases where the HPD
+		 * pulse signal got lost somewhere, even though the sink raised
+		 * the corresponding MST interrupt correctly. One example is the
+		 * Club 3D CAC-1557 TypeC -> DP adapter which for some reason
+		 * filters out short pulses with a duration less than ~540 usec.
+		 *
+		 * The poll period is 50 msec to avoid missing an interrupt
+		 * after the sink has cleared it (after a 110msec timeout
+		 * since it raised the interrupt).
+		 */
+		ret = wait_event_timeout(mgr->tx_waitq,
+					 check_txmsg_state(mgr, txmsg),
+					 mgr->cbs->poll_hpd_irq ?
+						msecs_to_jiffies(50) :
+						wait_timeout);
+
+		if (ret || !mgr->cbs->poll_hpd_irq ||
+		    time_after(jiffies, wait_expires))
+			break;
+
+		mgr->cbs->poll_hpd_irq(mgr);
+	}
+
+	mutex_lock(&mgr->qlock);
+	if (ret > 0) {
+		if (txmsg->state == DRM_DP_SIDEBAND_TX_TIMEOUT) {
+			ret = -EIO;
+			goto out;
+		}
+	} else {
+		drm_dbg_kms(mgr->dev, "timedout msg send %p %d %d\n",
+			    txmsg, txmsg->state, txmsg->seqno);
+
+		/* dump some state */
+		ret = -EIO;
+
+		/* remove from q */
+		if (txmsg->state == DRM_DP_SIDEBAND_TX_QUEUED ||
+		    txmsg->state == DRM_DP_SIDEBAND_TX_START_SEND ||
+		    txmsg->state == DRM_DP_SIDEBAND_TX_SENT)
+			list_del(&txmsg->next);
+	}
+out:
+	if (unlikely(ret == -EIO) && drm_debug_enabled(DRM_UT_DP)) {
+		struct drm_printer p = drm_debug_printer(DBG_PREFIX);
+
+		drm_dp_mst_dump_sideband_msg_tx(&p, txmsg);
+	}
+	mutex_unlock(&mgr->qlock);
+
+	drm_dp_mst_kick_tx(mgr);
+	return ret;
+}
+
+static struct drm_dp_mst_branch *drm_dp_add_mst_branch_device(u8 lct, u8 *rad)
+{
+	struct drm_dp_mst_branch *mstb;
+
+	mstb = kzalloc(sizeof(*mstb), GFP_KERNEL);
+	if (!mstb)
+		return NULL;
+
+	mstb->lct = lct;
+	if (lct > 1)
+		memcpy(mstb->rad, rad, lct / 2);
+	INIT_LIST_HEAD(&mstb->ports);
+	kref_init(&mstb->topology_kref);
+	kref_init(&mstb->malloc_kref);
+	return mstb;
+}
+
+static void drm_dp_free_mst_branch_device(struct kref *kref)
+{
+	struct drm_dp_mst_branch *mstb =
+		container_of(kref, struct drm_dp_mst_branch, malloc_kref);
+
+	if (mstb->port_parent)
+		drm_dp_mst_put_port_malloc(mstb->port_parent);
+
+	kfree(mstb);
+}
+
+/**
+ * DOC: Branch device and port refcounting
+ *
+ * Topology refcount overview
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~
+ *
+ * The refcounting schemes for &struct drm_dp_mst_branch and &struct
+ * drm_dp_mst_port are somewhat unusual. Both ports and branch devices have
+ * two different kinds of refcounts: topology refcounts, and malloc refcounts.
+ *
+ * Topology refcounts are not exposed to drivers, and are handled internally
+ * by the DP MST helpers. The helpers use them in order to prevent the
+ * in-memory topology state from being changed in the middle of critical
+ * operations like changing the internal state of payload allocations. This
+ * means each branch and port will be considered to be connected to the rest
+ * of the topology until its topology refcount reaches zero. Additionally,
+ * for ports this means that their associated &struct drm_connector will stay
+ * registered with userspace until the port's refcount reaches 0.
+ *
+ * Malloc refcount overview
+ * ~~~~~~~~~~~~~~~~~~~~~~~~
+ *
+ * Malloc references are used to keep a &struct drm_dp_mst_port or &struct
+ * drm_dp_mst_branch allocated even after all of its topology references have
+ * been dropped, so that the driver or MST helpers can safely access each
+ * branch's last known state before it was disconnected from the topology.
+ * When the malloc refcount of a port or branch reaches 0, the memory
+ * allocation containing the &struct drm_dp_mst_branch or &struct
+ * drm_dp_mst_port respectively will be freed.
+ *
+ * For &struct drm_dp_mst_branch, malloc refcounts are not currently exposed
+ * to drivers. As of writing this documentation, there are no drivers that
+ * have a usecase for accessing &struct drm_dp_mst_branch outside of the MST
+ * helpers. Exposing this API to drivers in a race-free manner would take more
+ * tweaking of the refcounting scheme, however patches are welcome provided
+ * there is a legitimate driver usecase for this.
+ *
+ * Refcount relationships in a topology
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ *
+ * Let's take a look at why the relationship between topology and malloc
+ * refcounts is designed the way it is.
+ *
+ * .. kernel-figure:: dp-mst/topology-figure-1.dot
+ *
+ *    An example of topology and malloc refs in a DP MST topology with two
+ *    active payloads. Topology refcount increments are indicated by solid
+ *    lines, and malloc refcount increments are indicated by dashed lines.
+ *    Each starts from the branch which incremented the refcount, and ends at
+ *    the branch to which the refcount belongs to, i.e. the arrow points the
+ *    same way as the C pointers used to reference a structure.
+ *
+ * As you can see in the above figure, every branch increments the topology
+ * refcount of its children, and increments the malloc refcount of its
+ * parent. Additionally, every payload increments the malloc refcount of its
+ * assigned port by 1.
+ *
+ * So, what would happen if MSTB #3 from the above figure was unplugged from
+ * the system, but the driver hadn't yet removed payload #2 from port #3? The
+ * topology would start to look like the figure below.
+ *
+ * .. kernel-figure:: dp-mst/topology-figure-2.dot
+ *
+ *    Ports and branch devices which have been released from memory are
+ *    colored grey, and references which have been removed are colored red.
+ *
+ * Whenever a port or branch device's topology refcount reaches zero, it will
+ * decrement the topology refcounts of all its children, the malloc refcount
+ * of its parent, and finally its own malloc refcount. For MSTB #4 and port
+ * #4, this means they both have been disconnected from the topology and freed
+ * from memory. But, because payload #2 is still holding a reference to port
+ * #3, port #3 is removed from the topology but its &struct drm_dp_mst_port
+ * is still accessible from memory. This also means port #3 has not yet
+ * decremented the malloc refcount of MSTB #3, so its &struct
+ * drm_dp_mst_branch will also stay allocated in memory until port #3's
+ * malloc refcount reaches 0.
+ *
+ * This relationship is necessary because in order to release payload #2, we
+ * need to be able to figure out the last relative of port #3 that's still
+ * connected to the topology. In this case, we would travel up the topology as
+ * shown below.
+ *
+ * .. kernel-figure:: dp-mst/topology-figure-3.dot
+ *
+ * And finally, remove payload #2 by communicating with port #2 through
+ * sideband transactions.
+ */
+
+/**
+ * drm_dp_mst_get_mstb_malloc() - Increment the malloc refcount of a branch
+ * device
+ * @mstb: The &struct drm_dp_mst_branch to increment the malloc refcount of
+ *
+ * Increments &drm_dp_mst_branch.malloc_kref. When
+ * &drm_dp_mst_branch.malloc_kref reaches 0, the memory allocation for @mstb
+ * will be released and @mstb may no longer be used.
+ *
+ * See also: drm_dp_mst_put_mstb_malloc()
+ */
+static void
+drm_dp_mst_get_mstb_malloc(struct drm_dp_mst_branch *mstb)
+{
+	kref_get(&mstb->malloc_kref);
+	drm_dbg(mstb->mgr->dev, "mstb %p (%d)\n", mstb, kref_read(&mstb->malloc_kref));
+}
+
+/**
+ * drm_dp_mst_put_mstb_malloc() - Decrement the malloc refcount of a branch
+ * device
+ * @mstb: The &struct drm_dp_mst_branch to decrement the malloc refcount of
+ *
+ * Decrements &drm_dp_mst_branch.malloc_kref. When
+ * &drm_dp_mst_branch.malloc_kref reaches 0, the memory allocation for @mstb
+ * will be released and @mstb may no longer be used.
+ *
+ * See also: drm_dp_mst_get_mstb_malloc()
+ */
+static void
+drm_dp_mst_put_mstb_malloc(struct drm_dp_mst_branch *mstb)
+{
+	drm_dbg(mstb->mgr->dev, "mstb %p (%d)\n", mstb, kref_read(&mstb->malloc_kref) - 1);
+	kref_put(&mstb->malloc_kref, drm_dp_free_mst_branch_device);
+}
+
+static void drm_dp_free_mst_port(struct kref *kref)
+{
+	struct drm_dp_mst_port *port =
+		container_of(kref, struct drm_dp_mst_port, malloc_kref);
+
+	drm_dp_mst_put_mstb_malloc(port->parent);
+	kfree(port);
+}
+
+/**
+ * drm_dp_mst_get_port_malloc() - Increment the malloc refcount of an MST port
+ * @port: The &struct drm_dp_mst_port to increment the malloc refcount of
+ *
+ * Increments &drm_dp_mst_port.malloc_kref. When &drm_dp_mst_port.malloc_kref
+ * reaches 0, the memory allocation for @port will be released and @port may
+ * no longer be used.
+ *
+ * Because @port could potentially be freed at any time by the DP MST helpers
+ * if &drm_dp_mst_port.malloc_kref reaches 0, including during a call to this
+ * function, drivers that which to make use of &struct drm_dp_mst_port should
+ * ensure that they grab at least one main malloc reference to their MST ports
+ * in &drm_dp_mst_topology_cbs.add_connector. This callback is called before
+ * there is any chance for &drm_dp_mst_port.malloc_kref to reach 0.
+ *
+ * See also: drm_dp_mst_put_port_malloc()
+ */
+void
+drm_dp_mst_get_port_malloc(struct drm_dp_mst_port *port)
+{
+	kref_get(&port->malloc_kref);
+	drm_dbg(port->mgr->dev, "port %p (%d)\n", port, kref_read(&port->malloc_kref));
+}
+EXPORT_SYMBOL(drm_dp_mst_get_port_malloc);
+
+/**
+ * drm_dp_mst_put_port_malloc() - Decrement the malloc refcount of an MST port
+ * @port: The &struct drm_dp_mst_port to decrement the malloc refcount of
+ *
+ * Decrements &drm_dp_mst_port.malloc_kref. When &drm_dp_mst_port.malloc_kref
+ * reaches 0, the memory allocation for @port will be released and @port may
+ * no longer be used.
+ *
+ * See also: drm_dp_mst_get_port_malloc()
+ */
+void
+drm_dp_mst_put_port_malloc(struct drm_dp_mst_port *port)
+{
+	drm_dbg(port->mgr->dev, "port %p (%d)\n", port, kref_read(&port->malloc_kref) - 1);
+	kref_put(&port->malloc_kref, drm_dp_free_mst_port);
+}
+EXPORT_SYMBOL(drm_dp_mst_put_port_malloc);
+
+#if IS_ENABLED(CONFIG_DRM_DEBUG_DP_MST_TOPOLOGY_REFS)
+
+#define STACK_DEPTH 8
+
+static noinline void
+__topology_ref_save(struct drm_dp_mst_topology_mgr *mgr,
+		    struct drm_dp_mst_topology_ref_history *history,
+		    enum drm_dp_mst_topology_ref_type type)
+{
+	struct drm_dp_mst_topology_ref_entry *entry = NULL;
+	depot_stack_handle_t backtrace;
+	ulong stack_entries[STACK_DEPTH];
+	uint n;
+	int i;
+
+	n = stack_trace_save(stack_entries, ARRAY_SIZE(stack_entries), 1);
+	backtrace = stack_depot_save(stack_entries, n, GFP_KERNEL);
+	if (!backtrace)
+		return;
+
+	/* Try to find an existing entry for this backtrace */
+	for (i = 0; i < history->len; i++) {
+		if (history->entries[i].backtrace == backtrace) {
+			entry = &history->entries[i];
+			break;
+		}
+	}
+
+	/* Otherwise add one */
+	if (!entry) {
+		struct drm_dp_mst_topology_ref_entry *new;
+		int new_len = history->len + 1;
+
+		new = krealloc(history->entries, sizeof(*new) * new_len,
+			       GFP_KERNEL);
+		if (!new)
+			return;
+
+		entry = &new[history->len];
+		history->len = new_len;
+		history->entries = new;
+
+		entry->backtrace = backtrace;
+		entry->type = type;
+		entry->count = 0;
+	}
+	entry->count++;
+	entry->ts_nsec = ktime_get_ns();
+}
+
+static int
+topology_ref_history_cmp(const void *a, const void *b)
+{
+	const struct drm_dp_mst_topology_ref_entry *entry_a = a, *entry_b = b;
+
+	if (entry_a->ts_nsec > entry_b->ts_nsec)
+		return 1;
+	else if (entry_a->ts_nsec < entry_b->ts_nsec)
+		return -1;
+	else
+		return 0;
+}
+
+static inline const char *
+topology_ref_type_to_str(enum drm_dp_mst_topology_ref_type type)
+{
+	if (type == DRM_DP_MST_TOPOLOGY_REF_GET)
+		return "get";
+	else
+		return "put";
+}
+
+static void
+__dump_topology_ref_history(struct drm_dp_mst_topology_ref_history *history,
+			    void *ptr, const char *type_str)
+{
+	struct drm_printer p = drm_debug_printer(DBG_PREFIX);
+	char *buf = kzalloc(PAGE_SIZE, GFP_KERNEL);
+	int i;
+
+	if (!buf)
+		return;
+
+	if (!history->len)
+		goto out;
+
+	/* First, sort the list so that it goes from oldest to newest
+	 * reference entry
+	 */
+	sort(history->entries, history->len, sizeof(*history->entries),
+	     topology_ref_history_cmp, NULL);
+
+	drm_printf(&p, "%s (%p) topology count reached 0, dumping history:\n",
+		   type_str, ptr);
+
+	for (i = 0; i < history->len; i++) {
+		const struct drm_dp_mst_topology_ref_entry *entry =
+			&history->entries[i];
+		u64 ts_nsec = entry->ts_nsec;
+		u32 rem_nsec = do_div(ts_nsec, 1000000000);
+
+		stack_depot_snprint(entry->backtrace, buf, PAGE_SIZE, 4);
+
+		drm_printf(&p, "  %d %ss (last at %5llu.%06u):\n%s",
+			   entry->count,
+			   topology_ref_type_to_str(entry->type),
+			   ts_nsec, rem_nsec / 1000, buf);
+	}
+
+	/* Now free the history, since this is the only time we expose it */
+	kfree(history->entries);
+out:
+	kfree(buf);
+}
+
+static __always_inline void
+drm_dp_mst_dump_mstb_topology_history(struct drm_dp_mst_branch *mstb)
+{
+	__dump_topology_ref_history(&mstb->topology_ref_history, mstb,
+				    "MSTB");
+}
+
+static __always_inline void
+drm_dp_mst_dump_port_topology_history(struct drm_dp_mst_port *port)
+{
+	__dump_topology_ref_history(&port->topology_ref_history, port,
+				    "Port");
+}
+
+static __always_inline void
+save_mstb_topology_ref(struct drm_dp_mst_branch *mstb,
+		       enum drm_dp_mst_topology_ref_type type)
+{
+	__topology_ref_save(mstb->mgr, &mstb->topology_ref_history, type);
+}
+
+static __always_inline void
+save_port_topology_ref(struct drm_dp_mst_port *port,
+		       enum drm_dp_mst_topology_ref_type type)
+{
+	__topology_ref_save(port->mgr, &port->topology_ref_history, type);
+}
+
+static inline void
+topology_ref_history_lock(struct drm_dp_mst_topology_mgr *mgr)
+{
+	mutex_lock(&mgr->topology_ref_history_lock);
+}
+
+static inline void
+topology_ref_history_unlock(struct drm_dp_mst_topology_mgr *mgr)
+{
+	mutex_unlock(&mgr->topology_ref_history_lock);
+}
+#else
+static inline void
+topology_ref_history_lock(struct drm_dp_mst_topology_mgr *mgr) {}
+static inline void
+topology_ref_history_unlock(struct drm_dp_mst_topology_mgr *mgr) {}
+static inline void
+drm_dp_mst_dump_mstb_topology_history(struct drm_dp_mst_branch *mstb) {}
+static inline void
+drm_dp_mst_dump_port_topology_history(struct drm_dp_mst_port *port) {}
+#define save_mstb_topology_ref(mstb, type)
+#define save_port_topology_ref(port, type)
+#endif
+
+static void drm_dp_destroy_mst_branch_device(struct kref *kref)
+{
+	struct drm_dp_mst_branch *mstb =
+		container_of(kref, struct drm_dp_mst_branch, topology_kref);
+	struct drm_dp_mst_topology_mgr *mgr = mstb->mgr;
+
+	drm_dp_mst_dump_mstb_topology_history(mstb);
+
+	INIT_LIST_HEAD(&mstb->destroy_next);
+
+	/*
+	 * This can get called under mgr->mutex, so we need to perform the
+	 * actual destruction of the mstb in another worker
+	 */
+	mutex_lock(&mgr->delayed_destroy_lock);
+	list_add(&mstb->destroy_next, &mgr->destroy_branch_device_list);
+	mutex_unlock(&mgr->delayed_destroy_lock);
+	queue_work(mgr->delayed_destroy_wq, &mgr->delayed_destroy_work);
+}
+
+/**
+ * drm_dp_mst_topology_try_get_mstb() - Increment the topology refcount of a
+ * branch device unless it's zero
+ * @mstb: &struct drm_dp_mst_branch to increment the topology refcount of
+ *
+ * Attempts to grab a topology reference to @mstb, if it hasn't yet been
+ * removed from the topology (e.g. &drm_dp_mst_branch.topology_kref has
+ * reached 0). Holding a topology reference implies that a malloc reference
+ * will be held to @mstb as long as the user holds the topology reference.
+ *
+ * Care should be taken to ensure that the user has at least one malloc
+ * reference to @mstb. If you already have a topology reference to @mstb, you
+ * should use drm_dp_mst_topology_get_mstb() instead.
+ *
+ * See also:
+ * drm_dp_mst_topology_get_mstb()
+ * drm_dp_mst_topology_put_mstb()
+ *
+ * Returns:
+ * * 1: A topology reference was grabbed successfully
+ * * 0: @port is no longer in the topology, no reference was grabbed
+ */
+static int __must_check
+drm_dp_mst_topology_try_get_mstb(struct drm_dp_mst_branch *mstb)
+{
+	int ret;
+
+	topology_ref_history_lock(mstb->mgr);
+	ret = kref_get_unless_zero(&mstb->topology_kref);
+	if (ret) {
+		drm_dbg(mstb->mgr->dev, "mstb %p (%d)\n", mstb, kref_read(&mstb->topology_kref));
+		save_mstb_topology_ref(mstb, DRM_DP_MST_TOPOLOGY_REF_GET);
+	}
+
+	topology_ref_history_unlock(mstb->mgr);
+
+	return ret;
+}
+
+/**
+ * drm_dp_mst_topology_get_mstb() - Increment the topology refcount of a
+ * branch device
+ * @mstb: The &struct drm_dp_mst_branch to increment the topology refcount of
+ *
+ * Increments &drm_dp_mst_branch.topology_refcount without checking whether or
+ * not it's already reached 0. This is only valid to use in scenarios where
+ * you are already guaranteed to have at least one active topology reference
+ * to @mstb. Otherwise, drm_dp_mst_topology_try_get_mstb() must be used.
+ *
+ * See also:
+ * drm_dp_mst_topology_try_get_mstb()
+ * drm_dp_mst_topology_put_mstb()
+ */
+static void drm_dp_mst_topology_get_mstb(struct drm_dp_mst_branch *mstb)
+{
+	topology_ref_history_lock(mstb->mgr);
+
+	save_mstb_topology_ref(mstb, DRM_DP_MST_TOPOLOGY_REF_GET);
+	WARN_ON(kref_read(&mstb->topology_kref) == 0);
+	kref_get(&mstb->topology_kref);
+	drm_dbg(mstb->mgr->dev, "mstb %p (%d)\n", mstb, kref_read(&mstb->topology_kref));
+
+	topology_ref_history_unlock(mstb->mgr);
+}
+
+/**
+ * drm_dp_mst_topology_put_mstb() - release a topology reference to a branch
+ * device
+ * @mstb: The &struct drm_dp_mst_branch to release the topology reference from
+ *
+ * Releases a topology reference from @mstb by decrementing
+ * &drm_dp_mst_branch.topology_kref.
+ *
+ * See also:
+ * drm_dp_mst_topology_try_get_mstb()
+ * drm_dp_mst_topology_get_mstb()
+ */
+static void
+drm_dp_mst_topology_put_mstb(struct drm_dp_mst_branch *mstb)
+{
+	topology_ref_history_lock(mstb->mgr);
+
+	drm_dbg(mstb->mgr->dev, "mstb %p (%d)\n", mstb, kref_read(&mstb->topology_kref) - 1);
+	save_mstb_topology_ref(mstb, DRM_DP_MST_TOPOLOGY_REF_PUT);
+
+	topology_ref_history_unlock(mstb->mgr);
+	kref_put(&mstb->topology_kref, drm_dp_destroy_mst_branch_device);
+}
+
+static void drm_dp_destroy_port(struct kref *kref)
+{
+	struct drm_dp_mst_port *port =
+		container_of(kref, struct drm_dp_mst_port, topology_kref);
+	struct drm_dp_mst_topology_mgr *mgr = port->mgr;
+
+	drm_dp_mst_dump_port_topology_history(port);
+
+	/* There's nothing that needs locking to destroy an input port yet */
+	if (port->input) {
+		drm_dp_mst_put_port_malloc(port);
+		return;
+	}
+
+	kfree(port->cached_edid);
+
+	/*
+	 * we can't destroy the connector here, as we might be holding the
+	 * mode_config.mutex from an EDID retrieval
+	 */
+	mutex_lock(&mgr->delayed_destroy_lock);
+	list_add(&port->next, &mgr->destroy_port_list);
+	mutex_unlock(&mgr->delayed_destroy_lock);
+	queue_work(mgr->delayed_destroy_wq, &mgr->delayed_destroy_work);
+}
+
+/**
+ * drm_dp_mst_topology_try_get_port() - Increment the topology refcount of a
+ * port unless it's zero
+ * @port: &struct drm_dp_mst_port to increment the topology refcount of
+ *
+ * Attempts to grab a topology reference to @port, if it hasn't yet been
+ * removed from the topology (e.g. &drm_dp_mst_port.topology_kref has reached
+ * 0). Holding a topology reference implies that a malloc reference will be
+ * held to @port as long as the user holds the topology reference.
+ *
+ * Care should be taken to ensure that the user has at least one malloc
+ * reference to @port. If you already have a topology reference to @port, you
+ * should use drm_dp_mst_topology_get_port() instead.
+ *
+ * See also:
+ * drm_dp_mst_topology_get_port()
+ * drm_dp_mst_topology_put_port()
+ *
+ * Returns:
+ * * 1: A topology reference was grabbed successfully
+ * * 0: @port is no longer in the topology, no reference was grabbed
+ */
+static int __must_check
+drm_dp_mst_topology_try_get_port(struct drm_dp_mst_port *port)
+{
+	int ret;
+
+	topology_ref_history_lock(port->mgr);
+	ret = kref_get_unless_zero(&port->topology_kref);
+	if (ret) {
+		drm_dbg(port->mgr->dev, "port %p (%d)\n", port, kref_read(&port->topology_kref));
+		save_port_topology_ref(port, DRM_DP_MST_TOPOLOGY_REF_GET);
+	}
+
+	topology_ref_history_unlock(port->mgr);
+	return ret;
+}
+
+/**
+ * drm_dp_mst_topology_get_port() - Increment the topology refcount of a port
+ * @port: The &struct drm_dp_mst_port to increment the topology refcount of
+ *
+ * Increments &drm_dp_mst_port.topology_refcount without checking whether or
+ * not it's already reached 0. This is only valid to use in scenarios where
+ * you are already guaranteed to have at least one active topology reference
+ * to @port. Otherwise, drm_dp_mst_topology_try_get_port() must be used.
+ *
+ * See also:
+ * drm_dp_mst_topology_try_get_port()
+ * drm_dp_mst_topology_put_port()
+ */
+static void drm_dp_mst_topology_get_port(struct drm_dp_mst_port *port)
+{
+	topology_ref_history_lock(port->mgr);
+
+	WARN_ON(kref_read(&port->topology_kref) == 0);
+	kref_get(&port->topology_kref);
+	drm_dbg(port->mgr->dev, "port %p (%d)\n", port, kref_read(&port->topology_kref));
+	save_port_topology_ref(port, DRM_DP_MST_TOPOLOGY_REF_GET);
+
+	topology_ref_history_unlock(port->mgr);
+}
+
+/**
+ * drm_dp_mst_topology_put_port() - release a topology reference to a port
+ * @port: The &struct drm_dp_mst_port to release the topology reference from
+ *
+ * Releases a topology reference from @port by decrementing
+ * &drm_dp_mst_port.topology_kref.
+ *
+ * See also:
+ * drm_dp_mst_topology_try_get_port()
+ * drm_dp_mst_topology_get_port()
+ */
+static void drm_dp_mst_topology_put_port(struct drm_dp_mst_port *port)
+{
+	topology_ref_history_lock(port->mgr);
+
+	drm_dbg(port->mgr->dev, "port %p (%d)\n", port, kref_read(&port->topology_kref) - 1);
+	save_port_topology_ref(port, DRM_DP_MST_TOPOLOGY_REF_PUT);
+
+	topology_ref_history_unlock(port->mgr);
+	kref_put(&port->topology_kref, drm_dp_destroy_port);
+}
+
+static struct drm_dp_mst_branch *
+drm_dp_mst_topology_get_mstb_validated_locked(struct drm_dp_mst_branch *mstb,
+					      struct drm_dp_mst_branch *to_find)
+{
+	struct drm_dp_mst_port *port;
+	struct drm_dp_mst_branch *rmstb;
+
+	if (to_find == mstb)
+		return mstb;
+
+	list_for_each_entry(port, &mstb->ports, next) {
+		if (port->mstb) {
+			rmstb = drm_dp_mst_topology_get_mstb_validated_locked(
+			    port->mstb, to_find);
+			if (rmstb)
+				return rmstb;
+		}
+	}
+	return NULL;
+}
+
+static struct drm_dp_mst_branch *
+drm_dp_mst_topology_get_mstb_validated(struct drm_dp_mst_topology_mgr *mgr,
+				       struct drm_dp_mst_branch *mstb)
+{
+	struct drm_dp_mst_branch *rmstb = NULL;
+
+	mutex_lock(&mgr->lock);
+	if (mgr->mst_primary) {
+		rmstb = drm_dp_mst_topology_get_mstb_validated_locked(
+		    mgr->mst_primary, mstb);
+
+		if (rmstb && !drm_dp_mst_topology_try_get_mstb(rmstb))
+			rmstb = NULL;
+	}
+	mutex_unlock(&mgr->lock);
+	return rmstb;
+}
+
+static struct drm_dp_mst_port *
+drm_dp_mst_topology_get_port_validated_locked(struct drm_dp_mst_branch *mstb,
+					      struct drm_dp_mst_port *to_find)
+{
+	struct drm_dp_mst_port *port, *mport;
+
+	list_for_each_entry(port, &mstb->ports, next) {
+		if (port == to_find)
+			return port;
+
+		if (port->mstb) {
+			mport = drm_dp_mst_topology_get_port_validated_locked(
+			    port->mstb, to_find);
+			if (mport)
+				return mport;
+		}
+	}
+	return NULL;
+}
+
+static struct drm_dp_mst_port *
+drm_dp_mst_topology_get_port_validated(struct drm_dp_mst_topology_mgr *mgr,
+				       struct drm_dp_mst_port *port)
+{
+	struct drm_dp_mst_port *rport = NULL;
+
+	mutex_lock(&mgr->lock);
+	if (mgr->mst_primary) {
+		rport = drm_dp_mst_topology_get_port_validated_locked(
+		    mgr->mst_primary, port);
+
+		if (rport && !drm_dp_mst_topology_try_get_port(rport))
+			rport = NULL;
+	}
+	mutex_unlock(&mgr->lock);
+	return rport;
+}
+
+static struct drm_dp_mst_port *drm_dp_get_port(struct drm_dp_mst_branch *mstb, u8 port_num)
+{
+	struct drm_dp_mst_port *port;
+	int ret;
+
+	list_for_each_entry(port, &mstb->ports, next) {
+		if (port->port_num == port_num) {
+			ret = drm_dp_mst_topology_try_get_port(port);
+			return ret ? port : NULL;
+		}
+	}
+
+	return NULL;
+}
+
+/*
+ * calculate a new RAD for this MST branch device
+ * if parent has an LCT of 2 then it has 1 nibble of RAD,
+ * if parent has an LCT of 3 then it has 2 nibbles of RAD,
+ */
+static u8 drm_dp_calculate_rad(struct drm_dp_mst_port *port,
+				 u8 *rad)
+{
+	int parent_lct = port->parent->lct;
+	int shift = 4;
+	int idx = (parent_lct - 1) / 2;
+
+	if (parent_lct > 1) {
+		memcpy(rad, port->parent->rad, idx + 1);
+		shift = (parent_lct % 2) ? 4 : 0;
+	} else
+		rad[0] = 0;
+
+	rad[idx] |= port->port_num << shift;
+	return parent_lct + 1;
+}
+
+static bool drm_dp_mst_is_end_device(u8 pdt, bool mcs)
+{
+	switch (pdt) {
+	case DP_PEER_DEVICE_DP_LEGACY_CONV:
+	case DP_PEER_DEVICE_SST_SINK:
+		return true;
+	case DP_PEER_DEVICE_MST_BRANCHING:
+		/* For sst branch device */
+		if (!mcs)
+			return true;
+
+		return false;
+	}
+	return true;
+}
+
+static int
+drm_dp_port_set_pdt(struct drm_dp_mst_port *port, u8 new_pdt,
+		    bool new_mcs)
+{
+	struct drm_dp_mst_topology_mgr *mgr = port->mgr;
+	struct drm_dp_mst_branch *mstb;
+	u8 rad[8], lct;
+	int ret = 0;
+
+	if (port->pdt == new_pdt && port->mcs == new_mcs)
+		return 0;
+
+	/* Teardown the old pdt, if there is one */
+	if (port->pdt != DP_PEER_DEVICE_NONE) {
+		if (drm_dp_mst_is_end_device(port->pdt, port->mcs)) {
+			/*
+			 * If the new PDT would also have an i2c bus,
+			 * don't bother with reregistering it
+			 */
+			if (new_pdt != DP_PEER_DEVICE_NONE &&
+			    drm_dp_mst_is_end_device(new_pdt, new_mcs)) {
+				port->pdt = new_pdt;
+				port->mcs = new_mcs;
+				return 0;
+			}
+
+			/* remove i2c over sideband */
+			drm_dp_mst_unregister_i2c_bus(port);
+		} else {
+			mutex_lock(&mgr->lock);
+			drm_dp_mst_topology_put_mstb(port->mstb);
+			port->mstb = NULL;
+			mutex_unlock(&mgr->lock);
+		}
+	}
+
+	port->pdt = new_pdt;
+	port->mcs = new_mcs;
+
+	if (port->pdt != DP_PEER_DEVICE_NONE) {
+		if (drm_dp_mst_is_end_device(port->pdt, port->mcs)) {
+			/* add i2c over sideband */
+			ret = drm_dp_mst_register_i2c_bus(port);
+		} else {
+			lct = drm_dp_calculate_rad(port, rad);
+			mstb = drm_dp_add_mst_branch_device(lct, rad);
+			if (!mstb) {
+				ret = -ENOMEM;
+				drm_err(mgr->dev, "Failed to create MSTB for port %p", port);
+				goto out;
+			}
+
+			mutex_lock(&mgr->lock);
+			port->mstb = mstb;
+			mstb->mgr = port->mgr;
+			mstb->port_parent = port;
+
+			/*
+			 * Make sure this port's memory allocation stays
+			 * around until its child MSTB releases it
+			 */
+			drm_dp_mst_get_port_malloc(port);
+			mutex_unlock(&mgr->lock);
+
+			/* And make sure we send a link address for this */
+			ret = 1;
+		}
+	}
+
+out:
+	if (ret < 0)
+		port->pdt = DP_PEER_DEVICE_NONE;
+	return ret;
+}
+
+/**
+ * drm_dp_mst_dpcd_read() - read a series of bytes from the DPCD via sideband
+ * @aux: Fake sideband AUX CH
+ * @offset: address of the (first) register to read
+ * @buffer: buffer to store the register values
+ * @size: number of bytes in @buffer
+ *
+ * Performs the same functionality for remote devices via
+ * sideband messaging as drm_dp_dpcd_read() does for local
+ * devices via actual AUX CH.
+ *
+ * Return: Number of bytes read, or negative error code on failure.
+ */
+ssize_t drm_dp_mst_dpcd_read(struct drm_dp_aux *aux,
+			     unsigned int offset, void *buffer, size_t size)
+{
+	struct drm_dp_mst_port *port = container_of(aux, struct drm_dp_mst_port,
+						    aux);
+
+	return drm_dp_send_dpcd_read(port->mgr, port,
+				     offset, size, buffer);
+}
+
+/**
+ * drm_dp_mst_dpcd_write() - write a series of bytes to the DPCD via sideband
+ * @aux: Fake sideband AUX CH
+ * @offset: address of the (first) register to write
+ * @buffer: buffer containing the values to write
+ * @size: number of bytes in @buffer
+ *
+ * Performs the same functionality for remote devices via
+ * sideband messaging as drm_dp_dpcd_write() does for local
+ * devices via actual AUX CH.
+ *
+ * Return: number of bytes written on success, negative error code on failure.
+ */
+ssize_t drm_dp_mst_dpcd_write(struct drm_dp_aux *aux,
+			      unsigned int offset, void *buffer, size_t size)
+{
+	struct drm_dp_mst_port *port = container_of(aux, struct drm_dp_mst_port,
+						    aux);
+
+	return drm_dp_send_dpcd_write(port->mgr, port,
+				      offset, size, buffer);
+}
+
+static int drm_dp_check_mstb_guid(struct drm_dp_mst_branch *mstb, u8 *guid)
+{
+	int ret = 0;
+
+	memcpy(mstb->guid, guid, 16);
+
+	if (!drm_dp_validate_guid(mstb->mgr, mstb->guid)) {
+		if (mstb->port_parent) {
+			ret = drm_dp_send_dpcd_write(mstb->mgr,
+						     mstb->port_parent,
+						     DP_GUID, 16, mstb->guid);
+		} else {
+			ret = drm_dp_dpcd_write(mstb->mgr->aux,
+						DP_GUID, mstb->guid, 16);
+		}
+	}
+
+	if (ret < 16 && ret > 0)
+		return -EPROTO;
+
+	return ret == 16 ? 0 : ret;
+}
+
+static void build_mst_prop_path(const struct drm_dp_mst_branch *mstb,
+				int pnum,
+				char *proppath,
+				size_t proppath_size)
+{
+	int i;
+	char temp[8];
+
+	snprintf(proppath, proppath_size, "mst:%d", mstb->mgr->conn_base_id);
+	for (i = 0; i < (mstb->lct - 1); i++) {
+		int shift = (i % 2) ? 0 : 4;
+		int port_num = (mstb->rad[i / 2] >> shift) & 0xf;
+
+		snprintf(temp, sizeof(temp), "-%d", port_num);
+		strlcat(proppath, temp, proppath_size);
+	}
+	snprintf(temp, sizeof(temp), "-%d", pnum);
+	strlcat(proppath, temp, proppath_size);
+}
+
+/**
+ * drm_dp_mst_connector_late_register() - Late MST connector registration
+ * @connector: The MST connector
+ * @port: The MST port for this connector
+ *
+ * Helper to register the remote aux device for this MST port. Drivers should
+ * call this from their mst connector's late_register hook to enable MST aux
+ * devices.
+ *
+ * Return: 0 on success, negative error code on failure.
+ */
+int drm_dp_mst_connector_late_register(struct drm_connector *connector,
+				       struct drm_dp_mst_port *port)
+{
+	drm_dbg_kms(port->mgr->dev, "registering %s remote bus for %s\n",
+		    port->aux.name, connector->kdev->kobj.name);
+
+	port->aux.dev = connector->kdev;
+	return drm_dp_aux_register_devnode(&port->aux);
+}
+EXPORT_SYMBOL(drm_dp_mst_connector_late_register);
+
+/**
+ * drm_dp_mst_connector_early_unregister() - Early MST connector unregistration
+ * @connector: The MST connector
+ * @port: The MST port for this connector
+ *
+ * Helper to unregister the remote aux device for this MST port, registered by
+ * drm_dp_mst_connector_late_register(). Drivers should call this from their mst
+ * connector's early_unregister hook.
+ */
+void drm_dp_mst_connector_early_unregister(struct drm_connector *connector,
+					   struct drm_dp_mst_port *port)
+{
+	drm_dbg_kms(port->mgr->dev, "unregistering %s remote bus for %s\n",
+		    port->aux.name, connector->kdev->kobj.name);
+	drm_dp_aux_unregister_devnode(&port->aux);
+}
+EXPORT_SYMBOL(drm_dp_mst_connector_early_unregister);
+
+static void
+drm_dp_mst_port_add_connector(struct drm_dp_mst_branch *mstb,
+			      struct drm_dp_mst_port *port)
+{
+	struct drm_dp_mst_topology_mgr *mgr = port->mgr;
+	char proppath[255];
+	int ret;
+
+	build_mst_prop_path(mstb, port->port_num, proppath, sizeof(proppath));
+	port->connector = mgr->cbs->add_connector(mgr, port, proppath);
+	if (!port->connector) {
+		ret = -ENOMEM;
+		goto error;
+	}
+
+	if (port->pdt != DP_PEER_DEVICE_NONE &&
+	    drm_dp_mst_is_end_device(port->pdt, port->mcs) &&
+	    port->port_num >= DP_MST_LOGICAL_PORT_0)
+		port->cached_edid = drm_get_edid(port->connector,
+						 &port->aux.ddc);
+
+	drm_connector_register(port->connector);
+	return;
+
+error:
+	drm_err(mgr->dev, "Failed to create connector for port %p: %d\n", port, ret);
+}
+
+/*
+ * Drop a topology reference, and unlink the port from the in-memory topology
+ * layout
+ */
+static void
+drm_dp_mst_topology_unlink_port(struct drm_dp_mst_topology_mgr *mgr,
+				struct drm_dp_mst_port *port)
+{
+	mutex_lock(&mgr->lock);
+	port->parent->num_ports--;
+	list_del(&port->next);
+	mutex_unlock(&mgr->lock);
+	drm_dp_mst_topology_put_port(port);
+}
+
+static struct drm_dp_mst_port *
+drm_dp_mst_add_port(struct drm_device *dev,
+		    struct drm_dp_mst_topology_mgr *mgr,
+		    struct drm_dp_mst_branch *mstb, u8 port_number)
+{
+	struct drm_dp_mst_port *port = kzalloc(sizeof(*port), GFP_KERNEL);
+
+	if (!port)
+		return NULL;
+
+	kref_init(&port->topology_kref);
+	kref_init(&port->malloc_kref);
+	port->parent = mstb;
+	port->port_num = port_number;
+	port->mgr = mgr;
+	port->aux.name = "DPMST";
+	port->aux.dev = dev->dev;
+	port->aux.is_remote = true;
+
+	/* initialize the MST downstream port's AUX crc work queue */
+	port->aux.drm_dev = dev;
+	drm_dp_remote_aux_init(&port->aux);
+
+	/*
+	 * Make sure the memory allocation for our parent branch stays
+	 * around until our own memory allocation is released
+	 */
+	drm_dp_mst_get_mstb_malloc(mstb);
+
+	return port;
+}
+
+static int
+drm_dp_mst_handle_link_address_port(struct drm_dp_mst_branch *mstb,
+				    struct drm_device *dev,
+				    struct drm_dp_link_addr_reply_port *port_msg)
+{
+	struct drm_dp_mst_topology_mgr *mgr = mstb->mgr;
+	struct drm_dp_mst_port *port;
+	int old_ddps = 0, ret;
+	u8 new_pdt = DP_PEER_DEVICE_NONE;
+	bool new_mcs = 0;
+	bool created = false, send_link_addr = false, changed = false;
+
+	port = drm_dp_get_port(mstb, port_msg->port_number);
+	if (!port) {
+		port = drm_dp_mst_add_port(dev, mgr, mstb,
+					   port_msg->port_number);
+		if (!port)
+			return -ENOMEM;
+		created = true;
+		changed = true;
+	} else if (!port->input && port_msg->input_port && port->connector) {
+		/* Since port->connector can't be changed here, we create a
+		 * new port if input_port changes from 0 to 1
+		 */
+		drm_dp_mst_topology_unlink_port(mgr, port);
+		drm_dp_mst_topology_put_port(port);
+		port = drm_dp_mst_add_port(dev, mgr, mstb,
+					   port_msg->port_number);
+		if (!port)
+			return -ENOMEM;
+		changed = true;
+		created = true;
+	} else if (port->input && !port_msg->input_port) {
+		changed = true;
+	} else if (port->connector) {
+		/* We're updating a port that's exposed to userspace, so do it
+		 * under lock
+		 */
+		drm_modeset_lock(&mgr->base.lock, NULL);
+
+		old_ddps = port->ddps;
+		changed = port->ddps != port_msg->ddps ||
+			(port->ddps &&
+			 (port->ldps != port_msg->legacy_device_plug_status ||
+			  port->dpcd_rev != port_msg->dpcd_revision ||
+			  port->mcs != port_msg->mcs ||
+			  port->pdt != port_msg->peer_device_type ||
+			  port->num_sdp_stream_sinks !=
+			  port_msg->num_sdp_stream_sinks));
+	}
+
+	port->input = port_msg->input_port;
+	if (!port->input)
+		new_pdt = port_msg->peer_device_type;
+	new_mcs = port_msg->mcs;
+	port->ddps = port_msg->ddps;
+	port->ldps = port_msg->legacy_device_plug_status;
+	port->dpcd_rev = port_msg->dpcd_revision;
+	port->num_sdp_streams = port_msg->num_sdp_streams;
+	port->num_sdp_stream_sinks = port_msg->num_sdp_stream_sinks;
+
+	/* manage mstb port lists with mgr lock - take a reference
+	   for this list */
+	if (created) {
+		mutex_lock(&mgr->lock);
+		drm_dp_mst_topology_get_port(port);
+		list_add(&port->next, &mstb->ports);
+		mstb->num_ports++;
+		mutex_unlock(&mgr->lock);
+	}
+
+	/*
+	 * Reprobe PBN caps on both hotplug, and when re-probing the link
+	 * for our parent mstb
+	 */
+	if (old_ddps != port->ddps || !created) {
+		if (port->ddps && !port->input) {
+			ret = drm_dp_send_enum_path_resources(mgr, mstb,
+							      port);
+			if (ret == 1)
+				changed = true;
+		} else {
+			port->full_pbn = 0;
+		}
+	}
+
+	ret = drm_dp_port_set_pdt(port, new_pdt, new_mcs);
+	if (ret == 1) {
+		send_link_addr = true;
+	} else if (ret < 0) {
+		drm_err(dev, "Failed to change PDT on port %p: %d\n", port, ret);
+		goto fail;
+	}
+
+	/*
+	 * If this port wasn't just created, then we're reprobing because
+	 * we're coming out of suspend. In this case, always resend the link
+	 * address if there's an MSTB on this port
+	 */
+	if (!created && port->pdt == DP_PEER_DEVICE_MST_BRANCHING &&
+	    port->mcs)
+		send_link_addr = true;
+
+	if (port->connector)
+		drm_modeset_unlock(&mgr->base.lock);
+	else if (!port->input)
+		drm_dp_mst_port_add_connector(mstb, port);
+
+	if (send_link_addr && port->mstb) {
+		ret = drm_dp_send_link_address(mgr, port->mstb);
+		if (ret == 1) /* MSTB below us changed */
+			changed = true;
+		else if (ret < 0)
+			goto fail_put;
+	}
+
+	/* put reference to this port */
+	drm_dp_mst_topology_put_port(port);
+	return changed;
+
+fail:
+	drm_dp_mst_topology_unlink_port(mgr, port);
+	if (port->connector)
+		drm_modeset_unlock(&mgr->base.lock);
+fail_put:
+	drm_dp_mst_topology_put_port(port);
+	return ret;
+}
+
+static void
+drm_dp_mst_handle_conn_stat(struct drm_dp_mst_branch *mstb,
+			    struct drm_dp_connection_status_notify *conn_stat)
+{
+	struct drm_dp_mst_topology_mgr *mgr = mstb->mgr;
+	struct drm_dp_mst_port *port;
+	int old_ddps, ret;
+	u8 new_pdt;
+	bool new_mcs;
+	bool dowork = false, create_connector = false;
+
+	port = drm_dp_get_port(mstb, conn_stat->port_number);
+	if (!port)
+		return;
+
+	if (port->connector) {
+		if (!port->input && conn_stat->input_port) {
+			/*
+			 * We can't remove a connector from an already exposed
+			 * port, so just throw the port out and make sure we
+			 * reprobe the link address of it's parent MSTB
+			 */
+			drm_dp_mst_topology_unlink_port(mgr, port);
+			mstb->link_address_sent = false;
+			dowork = true;
+			goto out;
+		}
+
+		/* Locking is only needed if the port's exposed to userspace */
+		drm_modeset_lock(&mgr->base.lock, NULL);
+	} else if (port->input && !conn_stat->input_port) {
+		create_connector = true;
+		/* Reprobe link address so we get num_sdp_streams */
+		mstb->link_address_sent = false;
+		dowork = true;
+	}
+
+	old_ddps = port->ddps;
+	port->input = conn_stat->input_port;
+	port->ldps = conn_stat->legacy_device_plug_status;
+	port->ddps = conn_stat->displayport_device_plug_status;
+
+	if (old_ddps != port->ddps) {
+		if (port->ddps && !port->input)
+			drm_dp_send_enum_path_resources(mgr, mstb, port);
+		else
+			port->full_pbn = 0;
+	}
+
+	new_pdt = port->input ? DP_PEER_DEVICE_NONE : conn_stat->peer_device_type;
+	new_mcs = conn_stat->message_capability_status;
+	ret = drm_dp_port_set_pdt(port, new_pdt, new_mcs);
+	if (ret == 1) {
+		dowork = true;
+	} else if (ret < 0) {
+		drm_err(mgr->dev, "Failed to change PDT for port %p: %d\n", port, ret);
+		dowork = false;
+	}
+
+	if (port->connector)
+		drm_modeset_unlock(&mgr->base.lock);
+	else if (create_connector)
+		drm_dp_mst_port_add_connector(mstb, port);
+
+out:
+	drm_dp_mst_topology_put_port(port);
+	if (dowork)
+		queue_work(system_long_wq, &mstb->mgr->work);
+}
+
+static struct drm_dp_mst_branch *drm_dp_get_mst_branch_device(struct drm_dp_mst_topology_mgr *mgr,
+							       u8 lct, u8 *rad)
+{
+	struct drm_dp_mst_branch *mstb;
+	struct drm_dp_mst_port *port;
+	int i, ret;
+	/* find the port by iterating down */
+
+	mutex_lock(&mgr->lock);
+	mstb = mgr->mst_primary;
+
+	if (!mstb)
+		goto out;
+
+	for (i = 0; i < lct - 1; i++) {
+		int shift = (i % 2) ? 0 : 4;
+		int port_num = (rad[i / 2] >> shift) & 0xf;
+
+		list_for_each_entry(port, &mstb->ports, next) {
+			if (port->port_num == port_num) {
+				mstb = port->mstb;
+				if (!mstb) {
+					drm_err(mgr->dev,
+						"failed to lookup MSTB with lct %d, rad %02x\n",
+						lct, rad[0]);
+					goto out;
+				}
+
+				break;
+			}
+		}
+	}
+	ret = drm_dp_mst_topology_try_get_mstb(mstb);
+	if (!ret)
+		mstb = NULL;
+out:
+	mutex_unlock(&mgr->lock);
+	return mstb;
+}
+
+static struct drm_dp_mst_branch *get_mst_branch_device_by_guid_helper(
+	struct drm_dp_mst_branch *mstb,
+	const uint8_t *guid)
+{
+	struct drm_dp_mst_branch *found_mstb;
+	struct drm_dp_mst_port *port;
+
+	if (memcmp(mstb->guid, guid, 16) == 0)
+		return mstb;
+
+
+	list_for_each_entry(port, &mstb->ports, next) {
+		if (!port->mstb)
+			continue;
+
+		found_mstb = get_mst_branch_device_by_guid_helper(port->mstb, guid);
+
+		if (found_mstb)
+			return found_mstb;
+	}
+
+	return NULL;
+}
+
+static struct drm_dp_mst_branch *
+drm_dp_get_mst_branch_device_by_guid(struct drm_dp_mst_topology_mgr *mgr,
+				     const uint8_t *guid)
+{
+	struct drm_dp_mst_branch *mstb;
+	int ret;
+
+	/* find the port by iterating down */
+	mutex_lock(&mgr->lock);
+
+	mstb = get_mst_branch_device_by_guid_helper(mgr->mst_primary, guid);
+	if (mstb) {
+		ret = drm_dp_mst_topology_try_get_mstb(mstb);
+		if (!ret)
+			mstb = NULL;
+	}
+
+	mutex_unlock(&mgr->lock);
+	return mstb;
+}
+
+static int drm_dp_check_and_send_link_address(struct drm_dp_mst_topology_mgr *mgr,
+					       struct drm_dp_mst_branch *mstb)
+{
+	struct drm_dp_mst_port *port;
+	int ret;
+	bool changed = false;
+
+	if (!mstb->link_address_sent) {
+		ret = drm_dp_send_link_address(mgr, mstb);
+		if (ret == 1)
+			changed = true;
+		else if (ret < 0)
+			return ret;
+	}
+
+	list_for_each_entry(port, &mstb->ports, next) {
+		struct drm_dp_mst_branch *mstb_child = NULL;
+
+		if (port->input || !port->ddps)
+			continue;
+
+		if (port->mstb)
+			mstb_child = drm_dp_mst_topology_get_mstb_validated(
+			    mgr, port->mstb);
+
+		if (mstb_child) {
+			ret = drm_dp_check_and_send_link_address(mgr,
+								 mstb_child);
+			drm_dp_mst_topology_put_mstb(mstb_child);
+			if (ret == 1)
+				changed = true;
+			else if (ret < 0)
+				return ret;
+		}
+	}
+
+	return changed;
+}
+
+static void drm_dp_mst_link_probe_work(struct work_struct *work)
+{
+	struct drm_dp_mst_topology_mgr *mgr =
+		container_of(work, struct drm_dp_mst_topology_mgr, work);
+	struct drm_device *dev = mgr->dev;
+	struct drm_dp_mst_branch *mstb;
+	int ret;
+	bool clear_payload_id_table;
+
+	mutex_lock(&mgr->probe_lock);
+
+	mutex_lock(&mgr->lock);
+	clear_payload_id_table = !mgr->payload_id_table_cleared;
+	mgr->payload_id_table_cleared = true;
+
+	mstb = mgr->mst_primary;
+	if (mstb) {
+		ret = drm_dp_mst_topology_try_get_mstb(mstb);
+		if (!ret)
+			mstb = NULL;
+	}
+	mutex_unlock(&mgr->lock);
+	if (!mstb) {
+		mutex_unlock(&mgr->probe_lock);
+		return;
+	}
+
+	/*
+	 * Certain branch devices seem to incorrectly report an available_pbn
+	 * of 0 on downstream sinks, even after clearing the
+	 * DP_PAYLOAD_ALLOCATE_* registers in
+	 * drm_dp_mst_topology_mgr_set_mst(). Namely, the CableMatters USB-C
+	 * 2x DP hub. Sending a CLEAR_PAYLOAD_ID_TABLE message seems to make
+	 * things work again.
+	 */
+	if (clear_payload_id_table) {
+		drm_dbg_kms(dev, "Clearing payload ID table\n");
+		drm_dp_send_clear_payload_id_table(mgr, mstb);
+	}
+
+	ret = drm_dp_check_and_send_link_address(mgr, mstb);
+	drm_dp_mst_topology_put_mstb(mstb);
+
+	mutex_unlock(&mgr->probe_lock);
+	if (ret > 0)
+		drm_kms_helper_hotplug_event(dev);
+}
+
+static bool drm_dp_validate_guid(struct drm_dp_mst_topology_mgr *mgr,
+				 u8 *guid)
+{
+	u64 salt;
+
+	if (memchr_inv(guid, 0, 16))
+		return true;
+
+	salt = get_jiffies_64();
+
+	memcpy(&guid[0], &salt, sizeof(u64));
+	memcpy(&guid[8], &salt, sizeof(u64));
+
+	return false;
+}
+
+static void build_dpcd_read(struct drm_dp_sideband_msg_tx *msg,
+			    u8 port_num, u32 offset, u8 num_bytes)
+{
+	struct drm_dp_sideband_msg_req_body req;
+
+	req.req_type = DP_REMOTE_DPCD_READ;
+	req.u.dpcd_read.port_number = port_num;
+	req.u.dpcd_read.dpcd_address = offset;
+	req.u.dpcd_read.num_bytes = num_bytes;
+	drm_dp_encode_sideband_req(&req, msg);
+}
+
+static int drm_dp_send_sideband_msg(struct drm_dp_mst_topology_mgr *mgr,
+				    bool up, u8 *msg, int len)
+{
+	int ret;
+	int regbase = up ? DP_SIDEBAND_MSG_UP_REP_BASE : DP_SIDEBAND_MSG_DOWN_REQ_BASE;
+	int tosend, total, offset;
+	int retries = 0;
+
+retry:
+	total = len;
+	offset = 0;
+	do {
+		tosend = min3(mgr->max_dpcd_transaction_bytes, 16, total);
+
+		ret = drm_dp_dpcd_write(mgr->aux, regbase + offset,
+					&msg[offset],
+					tosend);
+		if (ret != tosend) {
+			if (ret == -EIO && retries < 5) {
+				retries++;
+				goto retry;
+			}
+			drm_dbg_kms(mgr->dev, "failed to dpcd write %d %d\n", tosend, ret);
+
+			return -EIO;
+		}
+		offset += tosend;
+		total -= tosend;
+	} while (total > 0);
+	return 0;
+}
+
+static int set_hdr_from_dst_qlock(struct drm_dp_sideband_msg_hdr *hdr,
+				  struct drm_dp_sideband_msg_tx *txmsg)
+{
+	struct drm_dp_mst_branch *mstb = txmsg->dst;
+	u8 req_type;
+
+	req_type = txmsg->msg[0] & 0x7f;
+	if (req_type == DP_CONNECTION_STATUS_NOTIFY ||
+		req_type == DP_RESOURCE_STATUS_NOTIFY ||
+		req_type == DP_CLEAR_PAYLOAD_ID_TABLE)
+		hdr->broadcast = 1;
+	else
+		hdr->broadcast = 0;
+	hdr->path_msg = txmsg->path_msg;
+	if (hdr->broadcast) {
+		hdr->lct = 1;
+		hdr->lcr = 6;
+	} else {
+		hdr->lct = mstb->lct;
+		hdr->lcr = mstb->lct - 1;
+	}
+
+	memcpy(hdr->rad, mstb->rad, hdr->lct / 2);
+
+	return 0;
+}
+/*
+ * process a single block of the next message in the sideband queue
+ */
+static int process_single_tx_qlock(struct drm_dp_mst_topology_mgr *mgr,
+				   struct drm_dp_sideband_msg_tx *txmsg,
+				   bool up)
+{
+	u8 chunk[48];
+	struct drm_dp_sideband_msg_hdr hdr;
+	int len, space, idx, tosend;
+	int ret;
+
+	if (txmsg->state == DRM_DP_SIDEBAND_TX_SENT)
+		return 0;
+
+	memset(&hdr, 0, sizeof(struct drm_dp_sideband_msg_hdr));
+
+	if (txmsg->state == DRM_DP_SIDEBAND_TX_QUEUED)
+		txmsg->state = DRM_DP_SIDEBAND_TX_START_SEND;
+
+	/* make hdr from dst mst */
+	ret = set_hdr_from_dst_qlock(&hdr, txmsg);
+	if (ret < 0)
+		return ret;
+
+	/* amount left to send in this message */
+	len = txmsg->cur_len - txmsg->cur_offset;
+
+	/* 48 - sideband msg size - 1 byte for data CRC, x header bytes */
+	space = 48 - 1 - drm_dp_calc_sb_hdr_size(&hdr);
+
+	tosend = min(len, space);
+	if (len == txmsg->cur_len)
+		hdr.somt = 1;
+	if (space >= len)
+		hdr.eomt = 1;
+
+
+	hdr.msg_len = tosend + 1;
+	drm_dp_encode_sideband_msg_hdr(&hdr, chunk, &idx);
+	memcpy(&chunk[idx], &txmsg->msg[txmsg->cur_offset], tosend);
+	/* add crc at end */
+	drm_dp_crc_sideband_chunk_req(&chunk[idx], tosend);
+	idx += tosend + 1;
+
+	ret = drm_dp_send_sideband_msg(mgr, up, chunk, idx);
+	if (ret) {
+		if (drm_debug_enabled(DRM_UT_DP)) {
+			struct drm_printer p = drm_debug_printer(DBG_PREFIX);
+
+			drm_printf(&p, "sideband msg failed to send\n");
+			drm_dp_mst_dump_sideband_msg_tx(&p, txmsg);
+		}
+		return ret;
+	}
+
+	txmsg->cur_offset += tosend;
+	if (txmsg->cur_offset == txmsg->cur_len) {
+		txmsg->state = DRM_DP_SIDEBAND_TX_SENT;
+		return 1;
+	}
+	return 0;
+}
+
+static void process_single_down_tx_qlock(struct drm_dp_mst_topology_mgr *mgr)
+{
+	struct drm_dp_sideband_msg_tx *txmsg;
+	int ret;
+
+	WARN_ON(!mutex_is_locked(&mgr->qlock));
+
+	/* construct a chunk from the first msg in the tx_msg queue */
+	if (list_empty(&mgr->tx_msg_downq))
+		return;
+
+	txmsg = list_first_entry(&mgr->tx_msg_downq,
+				 struct drm_dp_sideband_msg_tx, next);
+	ret = process_single_tx_qlock(mgr, txmsg, false);
+	if (ret < 0) {
+		drm_dbg_kms(mgr->dev, "failed to send msg in q %d\n", ret);
+		list_del(&txmsg->next);
+		txmsg->state = DRM_DP_SIDEBAND_TX_TIMEOUT;
+		wake_up_all(&mgr->tx_waitq);
+	}
+}
+
+static void drm_dp_queue_down_tx(struct drm_dp_mst_topology_mgr *mgr,
+				 struct drm_dp_sideband_msg_tx *txmsg)
+{
+	mutex_lock(&mgr->qlock);
+	list_add_tail(&txmsg->next, &mgr->tx_msg_downq);
+
+	if (drm_debug_enabled(DRM_UT_DP)) {
+		struct drm_printer p = drm_debug_printer(DBG_PREFIX);
+
+		drm_dp_mst_dump_sideband_msg_tx(&p, txmsg);
+	}
+
+	if (list_is_singular(&mgr->tx_msg_downq))
+		process_single_down_tx_qlock(mgr);
+	mutex_unlock(&mgr->qlock);
+}
+
+static void
+drm_dp_dump_link_address(const struct drm_dp_mst_topology_mgr *mgr,
+			 struct drm_dp_link_address_ack_reply *reply)
+{
+	struct drm_dp_link_addr_reply_port *port_reply;
+	int i;
+
+	for (i = 0; i < reply->nports; i++) {
+		port_reply = &reply->ports[i];
+		drm_dbg_kms(mgr->dev,
+			    "port %d: input %d, pdt: %d, pn: %d, dpcd_rev: %02x, mcs: %d, ddps: %d, ldps %d, sdp %d/%d\n",
+			    i,
+			    port_reply->input_port,
+			    port_reply->peer_device_type,
+			    port_reply->port_number,
+			    port_reply->dpcd_revision,
+			    port_reply->mcs,
+			    port_reply->ddps,
+			    port_reply->legacy_device_plug_status,
+			    port_reply->num_sdp_streams,
+			    port_reply->num_sdp_stream_sinks);
+	}
+}
+
+static int drm_dp_send_link_address(struct drm_dp_mst_topology_mgr *mgr,
+				     struct drm_dp_mst_branch *mstb)
+{
+	struct drm_dp_sideband_msg_tx *txmsg;
+	struct drm_dp_link_address_ack_reply *reply;
+	struct drm_dp_mst_port *port, *tmp;
+	int i, ret, port_mask = 0;
+	bool changed = false;
+
+	txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
+	if (!txmsg)
+		return -ENOMEM;
+
+	txmsg->dst = mstb;
+	build_link_address(txmsg);
+
+	mstb->link_address_sent = true;
+	drm_dp_queue_down_tx(mgr, txmsg);
+
+	/* FIXME: Actually do some real error handling here */
+	ret = drm_dp_mst_wait_tx_reply(mstb, txmsg);
+	if (ret <= 0) {
+		drm_err(mgr->dev, "Sending link address failed with %d\n", ret);
+		goto out;
+	}
+	if (txmsg->reply.reply_type == DP_SIDEBAND_REPLY_NAK) {
+		drm_err(mgr->dev, "link address NAK received\n");
+		ret = -EIO;
+		goto out;
+	}
+
+	reply = &txmsg->reply.u.link_addr;
+	drm_dbg_kms(mgr->dev, "link address reply: %d\n", reply->nports);
+	drm_dp_dump_link_address(mgr, reply);
+
+	ret = drm_dp_check_mstb_guid(mstb, reply->guid);
+	if (ret) {
+		char buf[64];
+
+		drm_dp_mst_rad_to_str(mstb->rad, mstb->lct, buf, sizeof(buf));
+		drm_err(mgr->dev, "GUID check on %s failed: %d\n", buf, ret);
+		goto out;
+	}
+
+	for (i = 0; i < reply->nports; i++) {
+		port_mask |= BIT(reply->ports[i].port_number);
+		ret = drm_dp_mst_handle_link_address_port(mstb, mgr->dev,
+							  &reply->ports[i]);
+		if (ret == 1)
+			changed = true;
+		else if (ret < 0)
+			goto out;
+	}
+
+	/* Prune any ports that are currently a part of mstb in our in-memory
+	 * topology, but were not seen in this link address. Usually this
+	 * means that they were removed while the topology was out of sync,
+	 * e.g. during suspend/resume
+	 */
+	mutex_lock(&mgr->lock);
+	list_for_each_entry_safe(port, tmp, &mstb->ports, next) {
+		if (port_mask & BIT(port->port_num))
+			continue;
+
+		drm_dbg_kms(mgr->dev, "port %d was not in link address, removing\n",
+			    port->port_num);
+		list_del(&port->next);
+		drm_dp_mst_topology_put_port(port);
+		changed = true;
+	}
+	mutex_unlock(&mgr->lock);
+
+out:
+	if (ret <= 0)
+		mstb->link_address_sent = false;
+	kfree(txmsg);
+	return ret < 0 ? ret : changed;
+}
+
+static void
+drm_dp_send_clear_payload_id_table(struct drm_dp_mst_topology_mgr *mgr,
+				   struct drm_dp_mst_branch *mstb)
+{
+	struct drm_dp_sideband_msg_tx *txmsg;
+	int ret;
+
+	txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
+	if (!txmsg)
+		return;
+
+	txmsg->dst = mstb;
+	build_clear_payload_id_table(txmsg);
+
+	drm_dp_queue_down_tx(mgr, txmsg);
+
+	ret = drm_dp_mst_wait_tx_reply(mstb, txmsg);
+	if (ret > 0 && txmsg->reply.reply_type == DP_SIDEBAND_REPLY_NAK)
+		drm_dbg_kms(mgr->dev, "clear payload table id nak received\n");
+
+	kfree(txmsg);
+}
+
+static int
+drm_dp_send_enum_path_resources(struct drm_dp_mst_topology_mgr *mgr,
+				struct drm_dp_mst_branch *mstb,
+				struct drm_dp_mst_port *port)
+{
+	struct drm_dp_enum_path_resources_ack_reply *path_res;
+	struct drm_dp_sideband_msg_tx *txmsg;
+	int ret;
+
+	txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
+	if (!txmsg)
+		return -ENOMEM;
+
+	txmsg->dst = mstb;
+	build_enum_path_resources(txmsg, port->port_num);
+
+	drm_dp_queue_down_tx(mgr, txmsg);
+
+	ret = drm_dp_mst_wait_tx_reply(mstb, txmsg);
+	if (ret > 0) {
+		ret = 0;
+		path_res = &txmsg->reply.u.path_resources;
+
+		if (txmsg->reply.reply_type == DP_SIDEBAND_REPLY_NAK) {
+			drm_dbg_kms(mgr->dev, "enum path resources nak received\n");
+		} else {
+			if (port->port_num != path_res->port_number)
+				DRM_ERROR("got incorrect port in response\n");
+
+			drm_dbg_kms(mgr->dev, "enum path resources %d: %d %d\n",
+				    path_res->port_number,
+				    path_res->full_payload_bw_number,
+				    path_res->avail_payload_bw_number);
+
+			/*
+			 * If something changed, make sure we send a
+			 * hotplug
+			 */
+			if (port->full_pbn != path_res->full_payload_bw_number ||
+			    port->fec_capable != path_res->fec_capable)
+				ret = 1;
+
+			port->full_pbn = path_res->full_payload_bw_number;
+			port->fec_capable = path_res->fec_capable;
+		}
+	}
+
+	kfree(txmsg);
+	return ret;
+}
+
+static struct drm_dp_mst_port *drm_dp_get_last_connected_port_to_mstb(struct drm_dp_mst_branch *mstb)
+{
+	if (!mstb->port_parent)
+		return NULL;
+
+	if (mstb->port_parent->mstb != mstb)
+		return mstb->port_parent;
+
+	return drm_dp_get_last_connected_port_to_mstb(mstb->port_parent->parent);
+}
+
+/*
+ * Searches upwards in the topology starting from mstb to try to find the
+ * closest available parent of mstb that's still connected to the rest of the
+ * topology. This can be used in order to perform operations like releasing
+ * payloads, where the branch device which owned the payload may no longer be
+ * around and thus would require that the payload on the last living relative
+ * be freed instead.
+ */
+static struct drm_dp_mst_branch *
+drm_dp_get_last_connected_port_and_mstb(struct drm_dp_mst_topology_mgr *mgr,
+					struct drm_dp_mst_branch *mstb,
+					int *port_num)
+{
+	struct drm_dp_mst_branch *rmstb = NULL;
+	struct drm_dp_mst_port *found_port;
+
+	mutex_lock(&mgr->lock);
+	if (!mgr->mst_primary)
+		goto out;
+
+	do {
+		found_port = drm_dp_get_last_connected_port_to_mstb(mstb);
+		if (!found_port)
+			break;
+
+		if (drm_dp_mst_topology_try_get_mstb(found_port->parent)) {
+			rmstb = found_port->parent;
+			*port_num = found_port->port_num;
+		} else {
+			/* Search again, starting from this parent */
+			mstb = found_port->parent;
+		}
+	} while (!rmstb);
+out:
+	mutex_unlock(&mgr->lock);
+	return rmstb;
+}
+
+static int drm_dp_payload_send_msg(struct drm_dp_mst_topology_mgr *mgr,
+				   struct drm_dp_mst_port *port,
+				   int id,
+				   int pbn)
+{
+	struct drm_dp_sideband_msg_tx *txmsg;
+	struct drm_dp_mst_branch *mstb;
+	int ret, port_num;
+	u8 sinks[DRM_DP_MAX_SDP_STREAMS];
+	int i;
+
+	port_num = port->port_num;
+	mstb = drm_dp_mst_topology_get_mstb_validated(mgr, port->parent);
+	if (!mstb) {
+		mstb = drm_dp_get_last_connected_port_and_mstb(mgr,
+							       port->parent,
+							       &port_num);
+
+		if (!mstb)
+			return -EINVAL;
+	}
+
+	txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
+	if (!txmsg) {
+		ret = -ENOMEM;
+		goto fail_put;
+	}
+
+	for (i = 0; i < port->num_sdp_streams; i++)
+		sinks[i] = i;
+
+	txmsg->dst = mstb;
+	build_allocate_payload(txmsg, port_num,
+			       id,
+			       pbn, port->num_sdp_streams, sinks);
+
+	drm_dp_queue_down_tx(mgr, txmsg);
+
+	/*
+	 * FIXME: there is a small chance that between getting the last
+	 * connected mstb and sending the payload message, the last connected
+	 * mstb could also be removed from the topology. In the future, this
+	 * needs to be fixed by restarting the
+	 * drm_dp_get_last_connected_port_and_mstb() search in the event of a
+	 * timeout if the topology is still connected to the system.
+	 */
+	ret = drm_dp_mst_wait_tx_reply(mstb, txmsg);
+	if (ret > 0) {
+		if (txmsg->reply.reply_type == DP_SIDEBAND_REPLY_NAK)
+			ret = -EINVAL;
+		else
+			ret = 0;
+	}
+	kfree(txmsg);
+fail_put:
+	drm_dp_mst_topology_put_mstb(mstb);
+	return ret;
+}
+
+int drm_dp_send_power_updown_phy(struct drm_dp_mst_topology_mgr *mgr,
+				 struct drm_dp_mst_port *port, bool power_up)
+{
+	struct drm_dp_sideband_msg_tx *txmsg;
+	int ret;
+
+	port = drm_dp_mst_topology_get_port_validated(mgr, port);
+	if (!port)
+		return -EINVAL;
+
+	txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
+	if (!txmsg) {
+		drm_dp_mst_topology_put_port(port);
+		return -ENOMEM;
+	}
+
+	txmsg->dst = port->parent;
+	build_power_updown_phy(txmsg, port->port_num, power_up);
+	drm_dp_queue_down_tx(mgr, txmsg);
+
+	ret = drm_dp_mst_wait_tx_reply(port->parent, txmsg);
+	if (ret > 0) {
+		if (txmsg->reply.reply_type == DP_SIDEBAND_REPLY_NAK)
+			ret = -EINVAL;
+		else
+			ret = 0;
+	}
+	kfree(txmsg);
+	drm_dp_mst_topology_put_port(port);
+
+	return ret;
+}
+EXPORT_SYMBOL(drm_dp_send_power_updown_phy);
+
+int drm_dp_send_query_stream_enc_status(struct drm_dp_mst_topology_mgr *mgr,
+		struct drm_dp_mst_port *port,
+		struct drm_dp_query_stream_enc_status_ack_reply *status)
+{
+	struct drm_dp_sideband_msg_tx *txmsg;
+	u8 nonce[7];
+	int ret;
+
+	txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
+	if (!txmsg)
+		return -ENOMEM;
+
+	port = drm_dp_mst_topology_get_port_validated(mgr, port);
+	if (!port) {
+		ret = -EINVAL;
+		goto out_get_port;
+	}
+
+	get_random_bytes(nonce, sizeof(nonce));
+
+	/*
+	 * "Source device targets the QUERY_STREAM_ENCRYPTION_STATUS message
+	 *  transaction at the MST Branch device directly connected to the
+	 *  Source"
+	 */
+	txmsg->dst = mgr->mst_primary;
+
+	build_query_stream_enc_status(txmsg, port->vcpi.vcpi, nonce);
+
+	drm_dp_queue_down_tx(mgr, txmsg);
+
+	ret = drm_dp_mst_wait_tx_reply(mgr->mst_primary, txmsg);
+	if (ret < 0) {
+		goto out;
+	} else if (txmsg->reply.reply_type == DP_SIDEBAND_REPLY_NAK) {
+		drm_dbg_kms(mgr->dev, "query encryption status nak received\n");
+		ret = -ENXIO;
+		goto out;
+	}
+
+	ret = 0;
+	memcpy(status, &txmsg->reply.u.enc_status, sizeof(*status));
+
+out:
+	drm_dp_mst_topology_put_port(port);
+out_get_port:
+	kfree(txmsg);
+	return ret;
+}
+EXPORT_SYMBOL(drm_dp_send_query_stream_enc_status);
+
+static int drm_dp_create_payload_step1(struct drm_dp_mst_topology_mgr *mgr,
+				       int id,
+				       struct drm_dp_payload *payload)
+{
+	int ret;
+
+	ret = drm_dp_dpcd_write_payload(mgr, id, payload);
+	if (ret < 0) {
+		payload->payload_state = 0;
+		return ret;
+	}
+	payload->payload_state = DP_PAYLOAD_LOCAL;
+	return 0;
+}
+
+static int drm_dp_create_payload_step2(struct drm_dp_mst_topology_mgr *mgr,
+				       struct drm_dp_mst_port *port,
+				       int id,
+				       struct drm_dp_payload *payload)
+{
+	int ret;
+
+	ret = drm_dp_payload_send_msg(mgr, port, id, port->vcpi.pbn);
+	if (ret < 0)
+		return ret;
+	payload->payload_state = DP_PAYLOAD_REMOTE;
+	return ret;
+}
+
+static int drm_dp_destroy_payload_step1(struct drm_dp_mst_topology_mgr *mgr,
+					struct drm_dp_mst_port *port,
+					int id,
+					struct drm_dp_payload *payload)
+{
+	drm_dbg_kms(mgr->dev, "\n");
+	/* it's okay for these to fail */
+	if (port) {
+		drm_dp_payload_send_msg(mgr, port, id, 0);
+	}
+
+	drm_dp_dpcd_write_payload(mgr, id, payload);
+	payload->payload_state = DP_PAYLOAD_DELETE_LOCAL;
+	return 0;
+}
+
+static int drm_dp_destroy_payload_step2(struct drm_dp_mst_topology_mgr *mgr,
+					int id,
+					struct drm_dp_payload *payload)
+{
+	payload->payload_state = 0;
+	return 0;
+}
+
+/**
+ * drm_dp_update_payload_part1() - Execute payload update part 1
+ * @mgr: manager to use.
+ * @start_slot: this is the cur slot
+ *
+ * NOTE: start_slot is a temporary workaround for non-atomic drivers,
+ * this will be removed when non-atomic mst helpers are moved out of the helper
+ *
+ * This iterates over all proposed virtual channels, and tries to
+ * allocate space in the link for them. For 0->slots transitions,
+ * this step just writes the VCPI to the MST device. For slots->0
+ * transitions, this writes the updated VCPIs and removes the
+ * remote VC payloads.
+ *
+ * after calling this the driver should generate ACT and payload
+ * packets.
+ */
+int drm_dp_update_payload_part1(struct drm_dp_mst_topology_mgr *mgr, int start_slot)
+{
+	struct drm_dp_payload req_payload;
+	struct drm_dp_mst_port *port;
+	int i, j;
+	int cur_slots = start_slot;
+	bool skip;
+
+	mutex_lock(&mgr->payload_lock);
+	for (i = 0; i < mgr->max_payloads; i++) {
+		struct drm_dp_vcpi *vcpi = mgr->proposed_vcpis[i];
+		struct drm_dp_payload *payload = &mgr->payloads[i];
+		bool put_port = false;
+
+		/* solve the current payloads - compare to the hw ones
+		   - update the hw view */
+		req_payload.start_slot = cur_slots;
+		if (vcpi) {
+			port = container_of(vcpi, struct drm_dp_mst_port,
+					    vcpi);
+
+			mutex_lock(&mgr->lock);
+			skip = !drm_dp_mst_port_downstream_of_branch(port, mgr->mst_primary);
+			mutex_unlock(&mgr->lock);
+
+			if (skip) {
+				drm_dbg_kms(mgr->dev,
+					    "Virtual channel %d is not in current topology\n",
+					    i);
+				continue;
+			}
+			/* Validated ports don't matter if we're releasing
+			 * VCPI
+			 */
+			if (vcpi->num_slots) {
+				port = drm_dp_mst_topology_get_port_validated(
+				    mgr, port);
+				if (!port) {
+					if (vcpi->num_slots == payload->num_slots) {
+						cur_slots += vcpi->num_slots;
+						payload->start_slot = req_payload.start_slot;
+						continue;
+					} else {
+						drm_dbg_kms(mgr->dev,
+							    "Fail:set payload to invalid sink");
+						mutex_unlock(&mgr->payload_lock);
+						return -EINVAL;
+					}
+				}
+				put_port = true;
+			}
+
+			req_payload.num_slots = vcpi->num_slots;
+			req_payload.vcpi = vcpi->vcpi;
+		} else {
+			port = NULL;
+			req_payload.num_slots = 0;
+		}
+
+		payload->start_slot = req_payload.start_slot;
+		/* work out what is required to happen with this payload */
+		if (payload->num_slots != req_payload.num_slots) {
+
+			/* need to push an update for this payload */
+			if (req_payload.num_slots) {
+				drm_dp_create_payload_step1(mgr, vcpi->vcpi,
+							    &req_payload);
+				payload->num_slots = req_payload.num_slots;
+				payload->vcpi = req_payload.vcpi;
+
+			} else if (payload->num_slots) {
+				payload->num_slots = 0;
+				drm_dp_destroy_payload_step1(mgr, port,
+							     payload->vcpi,
+							     payload);
+				req_payload.payload_state =
+					payload->payload_state;
+				payload->start_slot = 0;
+			}
+			payload->payload_state = req_payload.payload_state;
+		}
+		cur_slots += req_payload.num_slots;
+
+		if (put_port)
+			drm_dp_mst_topology_put_port(port);
+	}
+
+	for (i = 0; i < mgr->max_payloads; /* do nothing */) {
+		if (mgr->payloads[i].payload_state != DP_PAYLOAD_DELETE_LOCAL) {
+			i++;
+			continue;
+		}
+
+		drm_dbg_kms(mgr->dev, "removing payload %d\n", i);
+		for (j = i; j < mgr->max_payloads - 1; j++) {
+			mgr->payloads[j] = mgr->payloads[j + 1];
+			mgr->proposed_vcpis[j] = mgr->proposed_vcpis[j + 1];
+
+			if (mgr->proposed_vcpis[j] &&
+			    mgr->proposed_vcpis[j]->num_slots) {
+				set_bit(j + 1, &mgr->payload_mask);
+			} else {
+				clear_bit(j + 1, &mgr->payload_mask);
+			}
+		}
+
+		memset(&mgr->payloads[mgr->max_payloads - 1], 0,
+		       sizeof(struct drm_dp_payload));
+		mgr->proposed_vcpis[mgr->max_payloads - 1] = NULL;
+		clear_bit(mgr->max_payloads, &mgr->payload_mask);
+	}
+	mutex_unlock(&mgr->payload_lock);
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_dp_update_payload_part1);
+
+/**
+ * drm_dp_update_payload_part2() - Execute payload update part 2
+ * @mgr: manager to use.
+ *
+ * This iterates over all proposed virtual channels, and tries to
+ * allocate space in the link for them. For 0->slots transitions,
+ * this step writes the remote VC payload commands. For slots->0
+ * this just resets some internal state.
+ */
+int drm_dp_update_payload_part2(struct drm_dp_mst_topology_mgr *mgr)
+{
+	struct drm_dp_mst_port *port;
+	int i;
+	int ret = 0;
+	bool skip;
+
+	mutex_lock(&mgr->payload_lock);
+	for (i = 0; i < mgr->max_payloads; i++) {
+
+		if (!mgr->proposed_vcpis[i])
+			continue;
+
+		port = container_of(mgr->proposed_vcpis[i], struct drm_dp_mst_port, vcpi);
+
+		mutex_lock(&mgr->lock);
+		skip = !drm_dp_mst_port_downstream_of_branch(port, mgr->mst_primary);
+		mutex_unlock(&mgr->lock);
+
+		if (skip)
+			continue;
+
+		drm_dbg_kms(mgr->dev, "payload %d %d\n", i, mgr->payloads[i].payload_state);
+		if (mgr->payloads[i].payload_state == DP_PAYLOAD_LOCAL) {
+			ret = drm_dp_create_payload_step2(mgr, port, mgr->proposed_vcpis[i]->vcpi, &mgr->payloads[i]);
+		} else if (mgr->payloads[i].payload_state == DP_PAYLOAD_DELETE_LOCAL) {
+			ret = drm_dp_destroy_payload_step2(mgr, mgr->proposed_vcpis[i]->vcpi, &mgr->payloads[i]);
+		}
+		if (ret) {
+			mutex_unlock(&mgr->payload_lock);
+			return ret;
+		}
+	}
+	mutex_unlock(&mgr->payload_lock);
+	return 0;
+}
+EXPORT_SYMBOL(drm_dp_update_payload_part2);
+
+static int drm_dp_send_dpcd_read(struct drm_dp_mst_topology_mgr *mgr,
+				 struct drm_dp_mst_port *port,
+				 int offset, int size, u8 *bytes)
+{
+	int ret = 0;
+	struct drm_dp_sideband_msg_tx *txmsg;
+	struct drm_dp_mst_branch *mstb;
+
+	mstb = drm_dp_mst_topology_get_mstb_validated(mgr, port->parent);
+	if (!mstb)
+		return -EINVAL;
+
+	txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
+	if (!txmsg) {
+		ret = -ENOMEM;
+		goto fail_put;
+	}
+
+	build_dpcd_read(txmsg, port->port_num, offset, size);
+	txmsg->dst = port->parent;
+
+	drm_dp_queue_down_tx(mgr, txmsg);
+
+	ret = drm_dp_mst_wait_tx_reply(mstb, txmsg);
+	if (ret < 0)
+		goto fail_free;
+
+	/* DPCD read should never be NACKed */
+	if (txmsg->reply.reply_type == 1) {
+		drm_err(mgr->dev, "mstb %p port %d: DPCD read on addr 0x%x for %d bytes NAKed\n",
+			mstb, port->port_num, offset, size);
+		ret = -EIO;
+		goto fail_free;
+	}
+
+	if (txmsg->reply.u.remote_dpcd_read_ack.num_bytes != size) {
+		ret = -EPROTO;
+		goto fail_free;
+	}
+
+	ret = min_t(size_t, txmsg->reply.u.remote_dpcd_read_ack.num_bytes,
+		    size);
+	memcpy(bytes, txmsg->reply.u.remote_dpcd_read_ack.bytes, ret);
+
+fail_free:
+	kfree(txmsg);
+fail_put:
+	drm_dp_mst_topology_put_mstb(mstb);
+
+	return ret;
+}
+
+static int drm_dp_send_dpcd_write(struct drm_dp_mst_topology_mgr *mgr,
+				  struct drm_dp_mst_port *port,
+				  int offset, int size, u8 *bytes)
+{
+	int ret;
+	struct drm_dp_sideband_msg_tx *txmsg;
+	struct drm_dp_mst_branch *mstb;
+
+	mstb = drm_dp_mst_topology_get_mstb_validated(mgr, port->parent);
+	if (!mstb)
+		return -EINVAL;
+
+	txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
+	if (!txmsg) {
+		ret = -ENOMEM;
+		goto fail_put;
+	}
+
+	build_dpcd_write(txmsg, port->port_num, offset, size, bytes);
+	txmsg->dst = mstb;
+
+	drm_dp_queue_down_tx(mgr, txmsg);
+
+	ret = drm_dp_mst_wait_tx_reply(mstb, txmsg);
+	if (ret > 0) {
+		if (txmsg->reply.reply_type == DP_SIDEBAND_REPLY_NAK)
+			ret = -EIO;
+		else
+			ret = size;
+	}
+
+	kfree(txmsg);
+fail_put:
+	drm_dp_mst_topology_put_mstb(mstb);
+	return ret;
+}
+
+static int drm_dp_encode_up_ack_reply(struct drm_dp_sideband_msg_tx *msg, u8 req_type)
+{
+	struct drm_dp_sideband_msg_reply_body reply;
+
+	reply.reply_type = DP_SIDEBAND_REPLY_ACK;
+	reply.req_type = req_type;
+	drm_dp_encode_sideband_reply(&reply, msg);
+	return 0;
+}
+
+static int drm_dp_send_up_ack_reply(struct drm_dp_mst_topology_mgr *mgr,
+				    struct drm_dp_mst_branch *mstb,
+				    int req_type, bool broadcast)
+{
+	struct drm_dp_sideband_msg_tx *txmsg;
+
+	txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
+	if (!txmsg)
+		return -ENOMEM;
+
+	txmsg->dst = mstb;
+	drm_dp_encode_up_ack_reply(txmsg, req_type);
+
+	mutex_lock(&mgr->qlock);
+	/* construct a chunk from the first msg in the tx_msg queue */
+	process_single_tx_qlock(mgr, txmsg, true);
+	mutex_unlock(&mgr->qlock);
+
+	kfree(txmsg);
+	return 0;
+}
+
+/**
+ * drm_dp_get_vc_payload_bw - get the VC payload BW for an MST link
+ * @mgr: The &drm_dp_mst_topology_mgr to use
+ * @link_rate: link rate in 10kbits/s units
+ * @link_lane_count: lane count
+ *
+ * Calculate the total bandwidth of a MultiStream Transport link. The returned
+ * value is in units of PBNs/(timeslots/1 MTP). This value can be used to
+ * convert the number of PBNs required for a given stream to the number of
+ * timeslots this stream requires in each MTP.
+ */
+int drm_dp_get_vc_payload_bw(const struct drm_dp_mst_topology_mgr *mgr,
+			     int link_rate, int link_lane_count)
+{
+	if (link_rate == 0 || link_lane_count == 0)
+		drm_dbg_kms(mgr->dev, "invalid link rate/lane count: (%d / %d)\n",
+			    link_rate, link_lane_count);
+
+	/* See DP v2.0 2.6.4.2, VCPayload_Bandwidth_for_OneTimeSlotPer_MTP_Allocation */
+	return link_rate * link_lane_count / 54000;
+}
+EXPORT_SYMBOL(drm_dp_get_vc_payload_bw);
+
+/**
+ * drm_dp_read_mst_cap() - check whether or not a sink supports MST
+ * @aux: The DP AUX channel to use
+ * @dpcd: A cached copy of the DPCD capabilities for this sink
+ *
+ * Returns: %True if the sink supports MST, %false otherwise
+ */
+bool drm_dp_read_mst_cap(struct drm_dp_aux *aux,
+			 const u8 dpcd[DP_RECEIVER_CAP_SIZE])
+{
+	u8 mstm_cap;
+
+	if (dpcd[DP_DPCD_REV] < DP_DPCD_REV_12)
+		return false;
+
+	if (drm_dp_dpcd_readb(aux, DP_MSTM_CAP, &mstm_cap) != 1)
+		return false;
+
+	return mstm_cap & DP_MST_CAP;
+}
+EXPORT_SYMBOL(drm_dp_read_mst_cap);
+
+/**
+ * drm_dp_mst_topology_mgr_set_mst() - Set the MST state for a topology manager
+ * @mgr: manager to set state for
+ * @mst_state: true to enable MST on this connector - false to disable.
+ *
+ * This is called by the driver when it detects an MST capable device plugged
+ * into a DP MST capable port, or when a DP MST capable device is unplugged.
+ */
+int drm_dp_mst_topology_mgr_set_mst(struct drm_dp_mst_topology_mgr *mgr, bool mst_state)
+{
+	int ret = 0;
+	struct drm_dp_mst_branch *mstb = NULL;
+
+	mutex_lock(&mgr->payload_lock);
+	mutex_lock(&mgr->lock);
+	if (mst_state == mgr->mst_state)
+		goto out_unlock;
+
+	mgr->mst_state = mst_state;
+	/* set the device into MST mode */
+	if (mst_state) {
+		struct drm_dp_payload reset_pay;
+		int lane_count;
+		int link_rate;
+
+		WARN_ON(mgr->mst_primary);
+
+		/* get dpcd info */
+		ret = drm_dp_read_dpcd_caps(mgr->aux, mgr->dpcd);
+		if (ret < 0) {
+			drm_dbg_kms(mgr->dev, "%s: failed to read DPCD, ret %d\n",
+				    mgr->aux->name, ret);
+			goto out_unlock;
+		}
+
+		lane_count = min_t(int, mgr->dpcd[2] & DP_MAX_LANE_COUNT_MASK, mgr->max_lane_count);
+		link_rate = min_t(int, drm_dp_bw_code_to_link_rate(mgr->dpcd[1]), mgr->max_link_rate);
+		mgr->pbn_div = drm_dp_get_vc_payload_bw(mgr,
+							link_rate,
+							lane_count);
+		if (mgr->pbn_div == 0) {
+			ret = -EINVAL;
+			goto out_unlock;
+		}
+
+		/* add initial branch device at LCT 1 */
+		mstb = drm_dp_add_mst_branch_device(1, NULL);
+		if (mstb == NULL) {
+			ret = -ENOMEM;
+			goto out_unlock;
+		}
+		mstb->mgr = mgr;
+
+		/* give this the main reference */
+		mgr->mst_primary = mstb;
+		drm_dp_mst_topology_get_mstb(mgr->mst_primary);
+
+		ret = drm_dp_dpcd_writeb(mgr->aux, DP_MSTM_CTRL,
+					 DP_MST_EN |
+					 DP_UP_REQ_EN |
+					 DP_UPSTREAM_IS_SRC);
+		if (ret < 0)
+			goto out_unlock;
+
+		reset_pay.start_slot = 0;
+		reset_pay.num_slots = 0x3f;
+		drm_dp_dpcd_write_payload(mgr, 0, &reset_pay);
+
+		queue_work(system_long_wq, &mgr->work);
+
+		ret = 0;
+	} else {
+		/* disable MST on the device */
+		mstb = mgr->mst_primary;
+		mgr->mst_primary = NULL;
+		/* this can fail if the device is gone */
+		drm_dp_dpcd_writeb(mgr->aux, DP_MSTM_CTRL, 0);
+		ret = 0;
+		memset(mgr->payloads, 0,
+		       mgr->max_payloads * sizeof(mgr->payloads[0]));
+		memset(mgr->proposed_vcpis, 0,
+		       mgr->max_payloads * sizeof(mgr->proposed_vcpis[0]));
+		mgr->payload_mask = 0;
+		set_bit(0, &mgr->payload_mask);
+		mgr->vcpi_mask = 0;
+		mgr->payload_id_table_cleared = false;
+	}
+
+out_unlock:
+	mutex_unlock(&mgr->lock);
+	mutex_unlock(&mgr->payload_lock);
+	if (mstb)
+		drm_dp_mst_topology_put_mstb(mstb);
+	return ret;
+
+}
+EXPORT_SYMBOL(drm_dp_mst_topology_mgr_set_mst);
+
+static void
+drm_dp_mst_topology_mgr_invalidate_mstb(struct drm_dp_mst_branch *mstb)
+{
+	struct drm_dp_mst_port *port;
+
+	/* The link address will need to be re-sent on resume */
+	mstb->link_address_sent = false;
+
+	list_for_each_entry(port, &mstb->ports, next)
+		if (port->mstb)
+			drm_dp_mst_topology_mgr_invalidate_mstb(port->mstb);
+}
+
+/**
+ * drm_dp_mst_topology_mgr_suspend() - suspend the MST manager
+ * @mgr: manager to suspend
+ *
+ * This function tells the MST device that we can't handle UP messages
+ * anymore. This should stop it from sending any since we are suspended.
+ */
+void drm_dp_mst_topology_mgr_suspend(struct drm_dp_mst_topology_mgr *mgr)
+{
+	mutex_lock(&mgr->lock);
+	drm_dp_dpcd_writeb(mgr->aux, DP_MSTM_CTRL,
+			   DP_MST_EN | DP_UPSTREAM_IS_SRC);
+	mutex_unlock(&mgr->lock);
+	flush_work(&mgr->up_req_work);
+	flush_work(&mgr->work);
+	flush_work(&mgr->delayed_destroy_work);
+
+	mutex_lock(&mgr->lock);
+	if (mgr->mst_state && mgr->mst_primary)
+		drm_dp_mst_topology_mgr_invalidate_mstb(mgr->mst_primary);
+	mutex_unlock(&mgr->lock);
+}
+EXPORT_SYMBOL(drm_dp_mst_topology_mgr_suspend);
+
+/**
+ * drm_dp_mst_topology_mgr_resume() - resume the MST manager
+ * @mgr: manager to resume
+ * @sync: whether or not to perform topology reprobing synchronously
+ *
+ * This will fetch DPCD and see if the device is still there,
+ * if it is, it will rewrite the MSTM control bits, and return.
+ *
+ * If the device fails this returns -1, and the driver should do
+ * a full MST reprobe, in case we were undocked.
+ *
+ * During system resume (where it is assumed that the driver will be calling
+ * drm_atomic_helper_resume()) this function should be called beforehand with
+ * @sync set to true. In contexts like runtime resume where the driver is not
+ * expected to be calling drm_atomic_helper_resume(), this function should be
+ * called with @sync set to false in order to avoid deadlocking.
+ *
+ * Returns: -1 if the MST topology was removed while we were suspended, 0
+ * otherwise.
+ */
+int drm_dp_mst_topology_mgr_resume(struct drm_dp_mst_topology_mgr *mgr,
+				   bool sync)
+{
+	int ret;
+	u8 guid[16];
+
+	mutex_lock(&mgr->lock);
+	if (!mgr->mst_primary)
+		goto out_fail;
+
+	ret = drm_dp_dpcd_read(mgr->aux, DP_DPCD_REV, mgr->dpcd,
+			       DP_RECEIVER_CAP_SIZE);
+	if (ret != DP_RECEIVER_CAP_SIZE) {
+		drm_dbg_kms(mgr->dev, "dpcd read failed - undocked during suspend?\n");
+		goto out_fail;
+	}
+
+	ret = drm_dp_dpcd_writeb(mgr->aux, DP_MSTM_CTRL,
+				 DP_MST_EN |
+				 DP_UP_REQ_EN |
+				 DP_UPSTREAM_IS_SRC);
+	if (ret < 0) {
+		drm_dbg_kms(mgr->dev, "mst write failed - undocked during suspend?\n");
+		goto out_fail;
+	}
+
+	/* Some hubs forget their guids after they resume */
+	ret = drm_dp_dpcd_read(mgr->aux, DP_GUID, guid, 16);
+	if (ret != 16) {
+		drm_dbg_kms(mgr->dev, "dpcd read failed - undocked during suspend?\n");
+		goto out_fail;
+	}
+
+	ret = drm_dp_check_mstb_guid(mgr->mst_primary, guid);
+	if (ret) {
+		drm_dbg_kms(mgr->dev, "check mstb failed - undocked during suspend?\n");
+		goto out_fail;
+	}
+
+	/*
+	 * For the final step of resuming the topology, we need to bring the
+	 * state of our in-memory topology back into sync with reality. So,
+	 * restart the probing process as if we're probing a new hub
+	 */
+	queue_work(system_long_wq, &mgr->work);
+	mutex_unlock(&mgr->lock);
+
+	if (sync) {
+		drm_dbg_kms(mgr->dev,
+			    "Waiting for link probe work to finish re-syncing topology...\n");
+		flush_work(&mgr->work);
+	}
+
+	return 0;
+
+out_fail:
+	mutex_unlock(&mgr->lock);
+	return -1;
+}
+EXPORT_SYMBOL(drm_dp_mst_topology_mgr_resume);
+
+static bool
+drm_dp_get_one_sb_msg(struct drm_dp_mst_topology_mgr *mgr, bool up,
+		      struct drm_dp_mst_branch **mstb)
+{
+	int len;
+	u8 replyblock[32];
+	int replylen, curreply;
+	int ret;
+	u8 hdrlen;
+	struct drm_dp_sideband_msg_hdr hdr;
+	struct drm_dp_sideband_msg_rx *msg =
+		up ? &mgr->up_req_recv : &mgr->down_rep_recv;
+	int basereg = up ? DP_SIDEBAND_MSG_UP_REQ_BASE :
+			   DP_SIDEBAND_MSG_DOWN_REP_BASE;
+
+	if (!up)
+		*mstb = NULL;
+
+	len = min(mgr->max_dpcd_transaction_bytes, 16);
+	ret = drm_dp_dpcd_read(mgr->aux, basereg, replyblock, len);
+	if (ret != len) {
+		drm_dbg_kms(mgr->dev, "failed to read DPCD down rep %d %d\n", len, ret);
+		return false;
+	}
+
+	ret = drm_dp_decode_sideband_msg_hdr(mgr, &hdr, replyblock, len, &hdrlen);
+	if (ret == false) {
+		print_hex_dump(KERN_DEBUG, "failed hdr", DUMP_PREFIX_NONE, 16,
+			       1, replyblock, len, false);
+		drm_dbg_kms(mgr->dev, "ERROR: failed header\n");
+		return false;
+	}
+
+	if (!up) {
+		/* Caller is responsible for giving back this reference */
+		*mstb = drm_dp_get_mst_branch_device(mgr, hdr.lct, hdr.rad);
+		if (!*mstb) {
+			drm_dbg_kms(mgr->dev, "Got MST reply from unknown device %d\n", hdr.lct);
+			return false;
+		}
+	}
+
+	if (!drm_dp_sideband_msg_set_header(msg, &hdr, hdrlen)) {
+		drm_dbg_kms(mgr->dev, "sideband msg set header failed %d\n", replyblock[0]);
+		return false;
+	}
+
+	replylen = min(msg->curchunk_len, (u8)(len - hdrlen));
+	ret = drm_dp_sideband_append_payload(msg, replyblock + hdrlen, replylen);
+	if (!ret) {
+		drm_dbg_kms(mgr->dev, "sideband msg build failed %d\n", replyblock[0]);
+		return false;
+	}
+
+	replylen = msg->curchunk_len + msg->curchunk_hdrlen - len;
+	curreply = len;
+	while (replylen > 0) {
+		len = min3(replylen, mgr->max_dpcd_transaction_bytes, 16);
+		ret = drm_dp_dpcd_read(mgr->aux, basereg + curreply,
+				    replyblock, len);
+		if (ret != len) {
+			drm_dbg_kms(mgr->dev, "failed to read a chunk (len %d, ret %d)\n",
+				    len, ret);
+			return false;
+		}
+
+		ret = drm_dp_sideband_append_payload(msg, replyblock, len);
+		if (!ret) {
+			drm_dbg_kms(mgr->dev, "failed to build sideband msg\n");
+			return false;
+		}
+
+		curreply += len;
+		replylen -= len;
+	}
+	return true;
+}
+
+static int drm_dp_mst_handle_down_rep(struct drm_dp_mst_topology_mgr *mgr)
+{
+	struct drm_dp_sideband_msg_tx *txmsg;
+	struct drm_dp_mst_branch *mstb = NULL;
+	struct drm_dp_sideband_msg_rx *msg = &mgr->down_rep_recv;
+
+	if (!drm_dp_get_one_sb_msg(mgr, false, &mstb))
+		goto out;
+
+	/* Multi-packet message transmission, don't clear the reply */
+	if (!msg->have_eomt)
+		goto out;
+
+	/* find the message */
+	mutex_lock(&mgr->qlock);
+	txmsg = list_first_entry_or_null(&mgr->tx_msg_downq,
+					 struct drm_dp_sideband_msg_tx, next);
+	mutex_unlock(&mgr->qlock);
+
+	/* Were we actually expecting a response, and from this mstb? */
+	if (!txmsg || txmsg->dst != mstb) {
+		struct drm_dp_sideband_msg_hdr *hdr;
+
+		hdr = &msg->initial_hdr;
+		drm_dbg_kms(mgr->dev, "Got MST reply with no msg %p %d %d %02x %02x\n",
+			    mstb, hdr->seqno, hdr->lct, hdr->rad[0], msg->msg[0]);
+		goto out_clear_reply;
+	}
+
+	drm_dp_sideband_parse_reply(mgr, msg, &txmsg->reply);
+
+	if (txmsg->reply.reply_type == DP_SIDEBAND_REPLY_NAK) {
+		drm_dbg_kms(mgr->dev,
+			    "Got NAK reply: req 0x%02x (%s), reason 0x%02x (%s), nak data 0x%02x\n",
+			    txmsg->reply.req_type,
+			    drm_dp_mst_req_type_str(txmsg->reply.req_type),
+			    txmsg->reply.u.nak.reason,
+			    drm_dp_mst_nak_reason_str(txmsg->reply.u.nak.reason),
+			    txmsg->reply.u.nak.nak_data);
+	}
+
+	memset(msg, 0, sizeof(struct drm_dp_sideband_msg_rx));
+	drm_dp_mst_topology_put_mstb(mstb);
+
+	mutex_lock(&mgr->qlock);
+	txmsg->state = DRM_DP_SIDEBAND_TX_RX;
+	list_del(&txmsg->next);
+	mutex_unlock(&mgr->qlock);
+
+	wake_up_all(&mgr->tx_waitq);
+
+	return 0;
+
+out_clear_reply:
+	memset(msg, 0, sizeof(struct drm_dp_sideband_msg_rx));
+out:
+	if (mstb)
+		drm_dp_mst_topology_put_mstb(mstb);
+
+	return 0;
+}
+
+static inline bool
+drm_dp_mst_process_up_req(struct drm_dp_mst_topology_mgr *mgr,
+			  struct drm_dp_pending_up_req *up_req)
+{
+	struct drm_dp_mst_branch *mstb = NULL;
+	struct drm_dp_sideband_msg_req_body *msg = &up_req->msg;
+	struct drm_dp_sideband_msg_hdr *hdr = &up_req->hdr;
+	bool hotplug = false;
+
+	if (hdr->broadcast) {
+		const u8 *guid = NULL;
+
+		if (msg->req_type == DP_CONNECTION_STATUS_NOTIFY)
+			guid = msg->u.conn_stat.guid;
+		else if (msg->req_type == DP_RESOURCE_STATUS_NOTIFY)
+			guid = msg->u.resource_stat.guid;
+
+		if (guid)
+			mstb = drm_dp_get_mst_branch_device_by_guid(mgr, guid);
+	} else {
+		mstb = drm_dp_get_mst_branch_device(mgr, hdr->lct, hdr->rad);
+	}
+
+	if (!mstb) {
+		drm_dbg_kms(mgr->dev, "Got MST reply from unknown device %d\n", hdr->lct);
+		return false;
+	}
+
+	/* TODO: Add missing handler for DP_RESOURCE_STATUS_NOTIFY events */
+	if (msg->req_type == DP_CONNECTION_STATUS_NOTIFY) {
+		drm_dp_mst_handle_conn_stat(mstb, &msg->u.conn_stat);
+		hotplug = true;
+	}
+
+	drm_dp_mst_topology_put_mstb(mstb);
+	return hotplug;
+}
+
+static void drm_dp_mst_up_req_work(struct work_struct *work)
+{
+	struct drm_dp_mst_topology_mgr *mgr =
+		container_of(work, struct drm_dp_mst_topology_mgr,
+			     up_req_work);
+	struct drm_dp_pending_up_req *up_req;
+	bool send_hotplug = false;
+
+	mutex_lock(&mgr->probe_lock);
+	while (true) {
+		mutex_lock(&mgr->up_req_lock);
+		up_req = list_first_entry_or_null(&mgr->up_req_list,
+						  struct drm_dp_pending_up_req,
+						  next);
+		if (up_req)
+			list_del(&up_req->next);
+		mutex_unlock(&mgr->up_req_lock);
+
+		if (!up_req)
+			break;
+
+		send_hotplug |= drm_dp_mst_process_up_req(mgr, up_req);
+		kfree(up_req);
+	}
+	mutex_unlock(&mgr->probe_lock);
+
+	if (send_hotplug)
+		drm_kms_helper_hotplug_event(mgr->dev);
+}
+
+static int drm_dp_mst_handle_up_req(struct drm_dp_mst_topology_mgr *mgr)
+{
+	struct drm_dp_pending_up_req *up_req;
+
+	if (!drm_dp_get_one_sb_msg(mgr, true, NULL))
+		goto out;
+
+	if (!mgr->up_req_recv.have_eomt)
+		return 0;
+
+	up_req = kzalloc(sizeof(*up_req), GFP_KERNEL);
+	if (!up_req)
+		return -ENOMEM;
+
+	INIT_LIST_HEAD(&up_req->next);
+
+	drm_dp_sideband_parse_req(mgr, &mgr->up_req_recv, &up_req->msg);
+
+	if (up_req->msg.req_type != DP_CONNECTION_STATUS_NOTIFY &&
+	    up_req->msg.req_type != DP_RESOURCE_STATUS_NOTIFY) {
+		drm_dbg_kms(mgr->dev, "Received unknown up req type, ignoring: %x\n",
+			    up_req->msg.req_type);
+		kfree(up_req);
+		goto out;
+	}
+
+	drm_dp_send_up_ack_reply(mgr, mgr->mst_primary, up_req->msg.req_type,
+				 false);
+
+	if (up_req->msg.req_type == DP_CONNECTION_STATUS_NOTIFY) {
+		const struct drm_dp_connection_status_notify *conn_stat =
+			&up_req->msg.u.conn_stat;
+
+		drm_dbg_kms(mgr->dev, "Got CSN: pn: %d ldps:%d ddps: %d mcs: %d ip: %d pdt: %d\n",
+			    conn_stat->port_number,
+			    conn_stat->legacy_device_plug_status,
+			    conn_stat->displayport_device_plug_status,
+			    conn_stat->message_capability_status,
+			    conn_stat->input_port,
+			    conn_stat->peer_device_type);
+	} else if (up_req->msg.req_type == DP_RESOURCE_STATUS_NOTIFY) {
+		const struct drm_dp_resource_status_notify *res_stat =
+			&up_req->msg.u.resource_stat;
+
+		drm_dbg_kms(mgr->dev, "Got RSN: pn: %d avail_pbn %d\n",
+			    res_stat->port_number,
+			    res_stat->available_pbn);
+	}
+
+	up_req->hdr = mgr->up_req_recv.initial_hdr;
+	mutex_lock(&mgr->up_req_lock);
+	list_add_tail(&up_req->next, &mgr->up_req_list);
+	mutex_unlock(&mgr->up_req_lock);
+	queue_work(system_long_wq, &mgr->up_req_work);
+
+out:
+	memset(&mgr->up_req_recv, 0, sizeof(struct drm_dp_sideband_msg_rx));
+	return 0;
+}
+
+/**
+ * drm_dp_mst_hpd_irq() - MST hotplug IRQ notify
+ * @mgr: manager to notify irq for.
+ * @esi: 4 bytes from SINK_COUNT_ESI
+ * @handled: whether the hpd interrupt was consumed or not
+ *
+ * This should be called from the driver when it detects a short IRQ,
+ * along with the value of the DEVICE_SERVICE_IRQ_VECTOR_ESI0. The
+ * topology manager will process the sideband messages received as a result
+ * of this.
+ */
+int drm_dp_mst_hpd_irq(struct drm_dp_mst_topology_mgr *mgr, u8 *esi, bool *handled)
+{
+	int ret = 0;
+	int sc;
+	*handled = false;
+	sc = DP_GET_SINK_COUNT(esi[0]);
+
+	if (sc != mgr->sink_count) {
+		mgr->sink_count = sc;
+		*handled = true;
+	}
+
+	if (esi[1] & DP_DOWN_REP_MSG_RDY) {
+		ret = drm_dp_mst_handle_down_rep(mgr);
+		*handled = true;
+	}
+
+	if (esi[1] & DP_UP_REQ_MSG_RDY) {
+		ret |= drm_dp_mst_handle_up_req(mgr);
+		*handled = true;
+	}
+
+	drm_dp_mst_kick_tx(mgr);
+	return ret;
+}
+EXPORT_SYMBOL(drm_dp_mst_hpd_irq);
+
+/**
+ * drm_dp_mst_detect_port() - get connection status for an MST port
+ * @connector: DRM connector for this port
+ * @ctx: The acquisition context to use for grabbing locks
+ * @mgr: manager for this port
+ * @port: pointer to a port
+ *
+ * This returns the current connection state for a port.
+ */
+int
+drm_dp_mst_detect_port(struct drm_connector *connector,
+		       struct drm_modeset_acquire_ctx *ctx,
+		       struct drm_dp_mst_topology_mgr *mgr,
+		       struct drm_dp_mst_port *port)
+{
+	int ret;
+
+	/* we need to search for the port in the mgr in case it's gone */
+	port = drm_dp_mst_topology_get_port_validated(mgr, port);
+	if (!port)
+		return connector_status_disconnected;
+
+	ret = drm_modeset_lock(&mgr->base.lock, ctx);
+	if (ret)
+		goto out;
+
+	ret = connector_status_disconnected;
+
+	if (!port->ddps)
+		goto out;
+
+	switch (port->pdt) {
+	case DP_PEER_DEVICE_NONE:
+		break;
+	case DP_PEER_DEVICE_MST_BRANCHING:
+		if (!port->mcs)
+			ret = connector_status_connected;
+		break;
+
+	case DP_PEER_DEVICE_SST_SINK:
+		ret = connector_status_connected;
+		/* for logical ports - cache the EDID */
+		if (port->port_num >= DP_MST_LOGICAL_PORT_0 && !port->cached_edid)
+			port->cached_edid = drm_get_edid(connector, &port->aux.ddc);
+		break;
+	case DP_PEER_DEVICE_DP_LEGACY_CONV:
+		if (port->ldps)
+			ret = connector_status_connected;
+		break;
+	}
+out:
+	drm_dp_mst_topology_put_port(port);
+	return ret;
+}
+EXPORT_SYMBOL(drm_dp_mst_detect_port);
+
+/**
+ * drm_dp_mst_get_edid() - get EDID for an MST port
+ * @connector: toplevel connector to get EDID for
+ * @mgr: manager for this port
+ * @port: unverified pointer to a port.
+ *
+ * This returns an EDID for the port connected to a connector,
+ * It validates the pointer still exists so the caller doesn't require a
+ * reference.
+ */
+struct edid *drm_dp_mst_get_edid(struct drm_connector *connector, struct drm_dp_mst_topology_mgr *mgr, struct drm_dp_mst_port *port)
+{
+	struct edid *edid = NULL;
+
+	/* we need to search for the port in the mgr in case it's gone */
+	port = drm_dp_mst_topology_get_port_validated(mgr, port);
+	if (!port)
+		return NULL;
+
+	if (port->cached_edid)
+		edid = drm_edid_duplicate(port->cached_edid);
+	else {
+		edid = drm_get_edid(connector, &port->aux.ddc);
+	}
+	port->has_audio = drm_detect_monitor_audio(edid);
+	drm_dp_mst_topology_put_port(port);
+	return edid;
+}
+EXPORT_SYMBOL(drm_dp_mst_get_edid);
+
+/**
+ * drm_dp_find_vcpi_slots() - Find VCPI slots for this PBN value
+ * @mgr: manager to use
+ * @pbn: payload bandwidth to convert into slots.
+ *
+ * Calculate the number of VCPI slots that will be required for the given PBN
+ * value. This function is deprecated, and should not be used in atomic
+ * drivers.
+ *
+ * RETURNS:
+ * The total slots required for this port, or error.
+ */
+int drm_dp_find_vcpi_slots(struct drm_dp_mst_topology_mgr *mgr,
+			   int pbn)
+{
+	int num_slots;
+
+	num_slots = DIV_ROUND_UP(pbn, mgr->pbn_div);
+
+	/* max. time slots - one slot for MTP header */
+	if (num_slots > 63)
+		return -ENOSPC;
+	return num_slots;
+}
+EXPORT_SYMBOL(drm_dp_find_vcpi_slots);
+
+static int drm_dp_init_vcpi(struct drm_dp_mst_topology_mgr *mgr,
+			    struct drm_dp_vcpi *vcpi, int pbn, int slots)
+{
+	int ret;
+
+	vcpi->pbn = pbn;
+	vcpi->aligned_pbn = slots * mgr->pbn_div;
+	vcpi->num_slots = slots;
+
+	ret = drm_dp_mst_assign_payload_id(mgr, vcpi);
+	if (ret < 0)
+		return ret;
+	return 0;
+}
+
+/**
+ * drm_dp_atomic_find_vcpi_slots() - Find and add VCPI slots to the state
+ * @state: global atomic state
+ * @mgr: MST topology manager for the port
+ * @port: port to find vcpi slots for
+ * @pbn: bandwidth required for the mode in PBN
+ * @pbn_div: divider for DSC mode that takes FEC into account
+ *
+ * Allocates VCPI slots to @port, replacing any previous VCPI allocations it
+ * may have had. Any atomic drivers which support MST must call this function
+ * in their &drm_encoder_helper_funcs.atomic_check() callback to change the
+ * current VCPI allocation for the new state, but only when
+ * &drm_crtc_state.mode_changed or &drm_crtc_state.connectors_changed is set
+ * to ensure compatibility with userspace applications that still use the
+ * legacy modesetting UAPI.
+ *
+ * Allocations set by this function are not checked against the bandwidth
+ * restraints of @mgr until the driver calls drm_dp_mst_atomic_check().
+ *
+ * Additionally, it is OK to call this function multiple times on the same
+ * @port as needed. It is not OK however, to call this function and
+ * drm_dp_atomic_release_vcpi_slots() in the same atomic check phase.
+ *
+ * See also:
+ * drm_dp_atomic_release_vcpi_slots()
+ * drm_dp_mst_atomic_check()
+ *
+ * Returns:
+ * Total slots in the atomic state assigned for this port, or a negative error
+ * code if the port no longer exists
+ */
+int drm_dp_atomic_find_vcpi_slots(struct drm_atomic_state *state,
+				  struct drm_dp_mst_topology_mgr *mgr,
+				  struct drm_dp_mst_port *port, int pbn,
+				  int pbn_div)
+{
+	struct drm_dp_mst_topology_state *topology_state;
+	struct drm_dp_vcpi_allocation *pos, *vcpi = NULL;
+	int prev_slots, prev_bw, req_slots;
+
+	topology_state = drm_atomic_get_mst_topology_state(state, mgr);
+	if (IS_ERR(topology_state))
+		return PTR_ERR(topology_state);
+
+	/* Find the current allocation for this port, if any */
+	list_for_each_entry(pos, &topology_state->vcpis, next) {
+		if (pos->port == port) {
+			vcpi = pos;
+			prev_slots = vcpi->vcpi;
+			prev_bw = vcpi->pbn;
+
+			/*
+			 * This should never happen, unless the driver tries
+			 * releasing and allocating the same VCPI allocation,
+			 * which is an error
+			 */
+			if (WARN_ON(!prev_slots)) {
+				drm_err(mgr->dev,
+					"cannot allocate and release VCPI on [MST PORT:%p] in the same state\n",
+					port);
+				return -EINVAL;
+			}
+
+			break;
+		}
+	}
+	if (!vcpi) {
+		prev_slots = 0;
+		prev_bw = 0;
+	}
+
+	if (pbn_div <= 0)
+		pbn_div = mgr->pbn_div;
+
+	req_slots = DIV_ROUND_UP(pbn, pbn_div);
+
+	drm_dbg_atomic(mgr->dev, "[CONNECTOR:%d:%s] [MST PORT:%p] VCPI %d -> %d\n",
+		       port->connector->base.id, port->connector->name,
+		       port, prev_slots, req_slots);
+	drm_dbg_atomic(mgr->dev, "[CONNECTOR:%d:%s] [MST PORT:%p] PBN %d -> %d\n",
+		       port->connector->base.id, port->connector->name,
+		       port, prev_bw, pbn);
+
+	/* Add the new allocation to the state */
+	if (!vcpi) {
+		vcpi = kzalloc(sizeof(*vcpi), GFP_KERNEL);
+		if (!vcpi)
+			return -ENOMEM;
+
+		drm_dp_mst_get_port_malloc(port);
+		vcpi->port = port;
+		list_add(&vcpi->next, &topology_state->vcpis);
+	}
+	vcpi->vcpi = req_slots;
+	vcpi->pbn = pbn;
+
+	return req_slots;
+}
+EXPORT_SYMBOL(drm_dp_atomic_find_vcpi_slots);
+
+/**
+ * drm_dp_atomic_release_vcpi_slots() - Release allocated vcpi slots
+ * @state: global atomic state
+ * @mgr: MST topology manager for the port
+ * @port: The port to release the VCPI slots from
+ *
+ * Releases any VCPI slots that have been allocated to a port in the atomic
+ * state. Any atomic drivers which support MST must call this function in
+ * their &drm_connector_helper_funcs.atomic_check() callback when the
+ * connector will no longer have VCPI allocated (e.g. because its CRTC was
+ * removed) when it had VCPI allocated in the previous atomic state.
+ *
+ * It is OK to call this even if @port has been removed from the system.
+ * Additionally, it is OK to call this function multiple times on the same
+ * @port as needed. It is not OK however, to call this function and
+ * drm_dp_atomic_find_vcpi_slots() on the same @port in a single atomic check
+ * phase.
+ *
+ * See also:
+ * drm_dp_atomic_find_vcpi_slots()
+ * drm_dp_mst_atomic_check()
+ *
+ * Returns:
+ * 0 if all slots for this port were added back to
+ * &drm_dp_mst_topology_state.avail_slots or negative error code
+ */
+int drm_dp_atomic_release_vcpi_slots(struct drm_atomic_state *state,
+				     struct drm_dp_mst_topology_mgr *mgr,
+				     struct drm_dp_mst_port *port)
+{
+	struct drm_dp_mst_topology_state *topology_state;
+	struct drm_dp_vcpi_allocation *pos;
+	bool found = false;
+
+	topology_state = drm_atomic_get_mst_topology_state(state, mgr);
+	if (IS_ERR(topology_state))
+		return PTR_ERR(topology_state);
+
+	list_for_each_entry(pos, &topology_state->vcpis, next) {
+		if (pos->port == port) {
+			found = true;
+			break;
+		}
+	}
+	if (WARN_ON(!found)) {
+		drm_err(mgr->dev, "no VCPI for [MST PORT:%p] found in mst state %p\n",
+			port, &topology_state->base);
+		return -EINVAL;
+	}
+
+	drm_dbg_atomic(mgr->dev, "[MST PORT:%p] VCPI %d -> 0\n", port, pos->vcpi);
+	if (pos->vcpi) {
+		drm_dp_mst_put_port_malloc(port);
+		pos->vcpi = 0;
+		pos->pbn = 0;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_dp_atomic_release_vcpi_slots);
+
+/**
+ * drm_dp_mst_update_slots() - updates the slot info depending on the DP ecoding format
+ * @mst_state: mst_state to update
+ * @link_encoding_cap: the ecoding format on the link
+ */
+void drm_dp_mst_update_slots(struct drm_dp_mst_topology_state *mst_state, uint8_t link_encoding_cap)
+{
+	if (link_encoding_cap == DP_CAP_ANSI_128B132B) {
+		mst_state->total_avail_slots = 64;
+		mst_state->start_slot = 0;
+	} else {
+		mst_state->total_avail_slots = 63;
+		mst_state->start_slot = 1;
+	}
+
+	DRM_DEBUG_KMS("%s encoding format on mst_state 0x%p\n",
+		      (link_encoding_cap == DP_CAP_ANSI_128B132B) ? "128b/132b":"8b/10b",
+		      mst_state);
+}
+EXPORT_SYMBOL(drm_dp_mst_update_slots);
+
+/**
+ * drm_dp_mst_allocate_vcpi() - Allocate a virtual channel
+ * @mgr: manager for this port
+ * @port: port to allocate a virtual channel for.
+ * @pbn: payload bandwidth number to request
+ * @slots: returned number of slots for this PBN.
+ */
+bool drm_dp_mst_allocate_vcpi(struct drm_dp_mst_topology_mgr *mgr,
+			      struct drm_dp_mst_port *port, int pbn, int slots)
+{
+	int ret;
+
+	if (slots < 0)
+		return false;
+
+	port = drm_dp_mst_topology_get_port_validated(mgr, port);
+	if (!port)
+		return false;
+
+	if (port->vcpi.vcpi > 0) {
+		drm_dbg_kms(mgr->dev,
+			    "payload: vcpi %d already allocated for pbn %d - requested pbn %d\n",
+			    port->vcpi.vcpi, port->vcpi.pbn, pbn);
+		if (pbn == port->vcpi.pbn) {
+			drm_dp_mst_topology_put_port(port);
+			return true;
+		}
+	}
+
+	ret = drm_dp_init_vcpi(mgr, &port->vcpi, pbn, slots);
+	if (ret) {
+		drm_dbg_kms(mgr->dev, "failed to init vcpi slots=%d ret=%d\n",
+			    DIV_ROUND_UP(pbn, mgr->pbn_div), ret);
+		drm_dp_mst_topology_put_port(port);
+		goto out;
+	}
+	drm_dbg_kms(mgr->dev, "initing vcpi for pbn=%d slots=%d\n", pbn, port->vcpi.num_slots);
+
+	/* Keep port allocated until its payload has been removed */
+	drm_dp_mst_get_port_malloc(port);
+	drm_dp_mst_topology_put_port(port);
+	return true;
+out:
+	return false;
+}
+EXPORT_SYMBOL(drm_dp_mst_allocate_vcpi);
+
+int drm_dp_mst_get_vcpi_slots(struct drm_dp_mst_topology_mgr *mgr, struct drm_dp_mst_port *port)
+{
+	int slots = 0;
+
+	port = drm_dp_mst_topology_get_port_validated(mgr, port);
+	if (!port)
+		return slots;
+
+	slots = port->vcpi.num_slots;
+	drm_dp_mst_topology_put_port(port);
+	return slots;
+}
+EXPORT_SYMBOL(drm_dp_mst_get_vcpi_slots);
+
+/**
+ * drm_dp_mst_reset_vcpi_slots() - Reset number of slots to 0 for VCPI
+ * @mgr: manager for this port
+ * @port: unverified pointer to a port.
+ *
+ * This just resets the number of slots for the ports VCPI for later programming.
+ */
+void drm_dp_mst_reset_vcpi_slots(struct drm_dp_mst_topology_mgr *mgr, struct drm_dp_mst_port *port)
+{
+	/*
+	 * A port with VCPI will remain allocated until its VCPI is
+	 * released, no verified ref needed
+	 */
+
+	port->vcpi.num_slots = 0;
+}
+EXPORT_SYMBOL(drm_dp_mst_reset_vcpi_slots);
+
+/**
+ * drm_dp_mst_deallocate_vcpi() - deallocate a VCPI
+ * @mgr: manager for this port
+ * @port: port to deallocate vcpi for
+ *
+ * This can be called unconditionally, regardless of whether
+ * drm_dp_mst_allocate_vcpi() succeeded or not.
+ */
+void drm_dp_mst_deallocate_vcpi(struct drm_dp_mst_topology_mgr *mgr,
+				struct drm_dp_mst_port *port)
+{
+	bool skip;
+
+	if (!port->vcpi.vcpi)
+		return;
+
+	mutex_lock(&mgr->lock);
+	skip = !drm_dp_mst_port_downstream_of_branch(port, mgr->mst_primary);
+	mutex_unlock(&mgr->lock);
+
+	if (skip)
+		return;
+
+	drm_dp_mst_put_payload_id(mgr, port->vcpi.vcpi);
+	port->vcpi.num_slots = 0;
+	port->vcpi.pbn = 0;
+	port->vcpi.aligned_pbn = 0;
+	port->vcpi.vcpi = 0;
+	drm_dp_mst_put_port_malloc(port);
+}
+EXPORT_SYMBOL(drm_dp_mst_deallocate_vcpi);
+
+static int drm_dp_dpcd_write_payload(struct drm_dp_mst_topology_mgr *mgr,
+				     int id, struct drm_dp_payload *payload)
+{
+	u8 payload_alloc[3], status;
+	int ret;
+	int retries = 0;
+
+	drm_dp_dpcd_writeb(mgr->aux, DP_PAYLOAD_TABLE_UPDATE_STATUS,
+			   DP_PAYLOAD_TABLE_UPDATED);
+
+	payload_alloc[0] = id;
+	payload_alloc[1] = payload->start_slot;
+	payload_alloc[2] = payload->num_slots;
+
+	ret = drm_dp_dpcd_write(mgr->aux, DP_PAYLOAD_ALLOCATE_SET, payload_alloc, 3);
+	if (ret != 3) {
+		drm_dbg_kms(mgr->dev, "failed to write payload allocation %d\n", ret);
+		goto fail;
+	}
+
+retry:
+	ret = drm_dp_dpcd_readb(mgr->aux, DP_PAYLOAD_TABLE_UPDATE_STATUS, &status);
+	if (ret < 0) {
+		drm_dbg_kms(mgr->dev, "failed to read payload table status %d\n", ret);
+		goto fail;
+	}
+
+	if (!(status & DP_PAYLOAD_TABLE_UPDATED)) {
+		retries++;
+		if (retries < 20) {
+			usleep_range(10000, 20000);
+			goto retry;
+		}
+		drm_dbg_kms(mgr->dev, "status not set after read payload table status %d\n",
+			    status);
+		ret = -EINVAL;
+		goto fail;
+	}
+	ret = 0;
+fail:
+	return ret;
+}
+
+static int do_get_act_status(struct drm_dp_aux *aux)
+{
+	int ret;
+	u8 status;
+
+	ret = drm_dp_dpcd_readb(aux, DP_PAYLOAD_TABLE_UPDATE_STATUS, &status);
+	if (ret < 0)
+		return ret;
+
+	return status;
+}
+
+/**
+ * drm_dp_check_act_status() - Polls for ACT handled status.
+ * @mgr: manager to use
+ *
+ * Tries waiting for the MST hub to finish updating it's payload table by
+ * polling for the ACT handled bit for up to 3 seconds (yes-some hubs really
+ * take that long).
+ *
+ * Returns:
+ * 0 if the ACT was handled in time, negative error code on failure.
+ */
+int drm_dp_check_act_status(struct drm_dp_mst_topology_mgr *mgr)
+{
+	/*
+	 * There doesn't seem to be any recommended retry count or timeout in
+	 * the MST specification. Since some hubs have been observed to take
+	 * over 1 second to update their payload allocations under certain
+	 * conditions, we use a rather large timeout value.
+	 */
+	const int timeout_ms = 3000;
+	int ret, status;
+
+	ret = readx_poll_timeout(do_get_act_status, mgr->aux, status,
+				 status & DP_PAYLOAD_ACT_HANDLED || status < 0,
+				 200, timeout_ms * USEC_PER_MSEC);
+	if (ret < 0 && status >= 0) {
+		drm_err(mgr->dev, "Failed to get ACT after %dms, last status: %02x\n",
+			timeout_ms, status);
+		return -EINVAL;
+	} else if (status < 0) {
+		/*
+		 * Failure here isn't unexpected - the hub may have
+		 * just been unplugged
+		 */
+		drm_dbg_kms(mgr->dev, "Failed to read payload table status: %d\n", status);
+		return status;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_dp_check_act_status);
+
+/**
+ * drm_dp_calc_pbn_mode() - Calculate the PBN for a mode.
+ * @clock: dot clock for the mode
+ * @bpp: bpp for the mode.
+ * @dsc: DSC mode. If true, bpp has units of 1/16 of a bit per pixel
+ *
+ * This uses the formula in the spec to calculate the PBN value for a mode.
+ */
+int drm_dp_calc_pbn_mode(int clock, int bpp, bool dsc)
+{
+	/*
+	 * margin 5300ppm + 300ppm ~ 0.6% as per spec, factor is 1.006
+	 * The unit of 54/64Mbytes/sec is an arbitrary unit chosen based on
+	 * common multiplier to render an integer PBN for all link rate/lane
+	 * counts combinations
+	 * calculate
+	 * peak_kbps *= (1006/1000)
+	 * peak_kbps *= (64/54)
+	 * peak_kbps *= 8    convert to bytes
+	 *
+	 * If the bpp is in units of 1/16, further divide by 16. Put this
+	 * factor in the numerator rather than the denominator to avoid
+	 * integer overflow
+	 */
+
+	if (dsc)
+		return DIV_ROUND_UP_ULL(mul_u32_u32(clock * (bpp / 16), 64 * 1006),
+					8 * 54 * 1000 * 1000);
+
+	return DIV_ROUND_UP_ULL(mul_u32_u32(clock * bpp, 64 * 1006),
+				8 * 54 * 1000 * 1000);
+}
+EXPORT_SYMBOL(drm_dp_calc_pbn_mode);
+
+/* we want to kick the TX after we've ack the up/down IRQs. */
+static void drm_dp_mst_kick_tx(struct drm_dp_mst_topology_mgr *mgr)
+{
+	queue_work(system_long_wq, &mgr->tx_work);
+}
+
+/*
+ * Helper function for parsing DP device types into convenient strings
+ * for use with dp_mst_topology
+ */
+static const char *pdt_to_string(u8 pdt)
+{
+	switch (pdt) {
+	case DP_PEER_DEVICE_NONE:
+		return "NONE";
+	case DP_PEER_DEVICE_SOURCE_OR_SST:
+		return "SOURCE OR SST";
+	case DP_PEER_DEVICE_MST_BRANCHING:
+		return "MST BRANCHING";
+	case DP_PEER_DEVICE_SST_SINK:
+		return "SST SINK";
+	case DP_PEER_DEVICE_DP_LEGACY_CONV:
+		return "DP LEGACY CONV";
+	default:
+		return "ERR";
+	}
+}
+
+static void drm_dp_mst_dump_mstb(struct seq_file *m,
+				 struct drm_dp_mst_branch *mstb)
+{
+	struct drm_dp_mst_port *port;
+	int tabs = mstb->lct;
+	char prefix[10];
+	int i;
+
+	for (i = 0; i < tabs; i++)
+		prefix[i] = '\t';
+	prefix[i] = '\0';
+
+	seq_printf(m, "%smstb - [%p]: num_ports: %d\n", prefix, mstb, mstb->num_ports);
+	list_for_each_entry(port, &mstb->ports, next) {
+		seq_printf(m, "%sport %d - [%p] (%s - %s): ddps: %d, ldps: %d, sdp: %d/%d, fec: %s, conn: %p\n",
+			   prefix,
+			   port->port_num,
+			   port,
+			   port->input ? "input" : "output",
+			   pdt_to_string(port->pdt),
+			   port->ddps,
+			   port->ldps,
+			   port->num_sdp_streams,
+			   port->num_sdp_stream_sinks,
+			   port->fec_capable ? "true" : "false",
+			   port->connector);
+		if (port->mstb)
+			drm_dp_mst_dump_mstb(m, port->mstb);
+	}
+}
+
+#define DP_PAYLOAD_TABLE_SIZE		64
+
+static bool dump_dp_payload_table(struct drm_dp_mst_topology_mgr *mgr,
+				  char *buf)
+{
+	int i;
+
+	for (i = 0; i < DP_PAYLOAD_TABLE_SIZE; i += 16) {
+		if (drm_dp_dpcd_read(mgr->aux,
+				     DP_PAYLOAD_TABLE_UPDATE_STATUS + i,
+				     &buf[i], 16) != 16)
+			return false;
+	}
+	return true;
+}
+
+static void fetch_monitor_name(struct drm_dp_mst_topology_mgr *mgr,
+			       struct drm_dp_mst_port *port, char *name,
+			       int namelen)
+{
+	struct edid *mst_edid;
+
+	mst_edid = drm_dp_mst_get_edid(port->connector, mgr, port);
+	drm_edid_get_monitor_name(mst_edid, name, namelen);
+}
+
+/**
+ * drm_dp_mst_dump_topology(): dump topology to seq file.
+ * @m: seq_file to dump output to
+ * @mgr: manager to dump current topology for.
+ *
+ * helper to dump MST topology to a seq file for debugfs.
+ */
+void drm_dp_mst_dump_topology(struct seq_file *m,
+			      struct drm_dp_mst_topology_mgr *mgr)
+{
+	int i;
+	struct drm_dp_mst_port *port;
+
+	mutex_lock(&mgr->lock);
+	if (mgr->mst_primary)
+		drm_dp_mst_dump_mstb(m, mgr->mst_primary);
+
+	/* dump VCPIs */
+	mutex_unlock(&mgr->lock);
+
+	mutex_lock(&mgr->payload_lock);
+	seq_printf(m, "\n*** VCPI Info ***\n");
+	seq_printf(m, "payload_mask: %lx, vcpi_mask: %lx, max_payloads: %d\n", mgr->payload_mask, mgr->vcpi_mask, mgr->max_payloads);
+
+	seq_printf(m, "\n|   idx   |  port # |  vcp_id | # slots |     sink name     |\n");
+	for (i = 0; i < mgr->max_payloads; i++) {
+		if (mgr->proposed_vcpis[i]) {
+			char name[14];
+
+			port = container_of(mgr->proposed_vcpis[i], struct drm_dp_mst_port, vcpi);
+			fetch_monitor_name(mgr, port, name, sizeof(name));
+			seq_printf(m, "%10d%10d%10d%10d%20s\n",
+				   i,
+				   port->port_num,
+				   port->vcpi.vcpi,
+				   port->vcpi.num_slots,
+				   (*name != 0) ? name : "Unknown");
+		} else
+			seq_printf(m, "%6d - Unused\n", i);
+	}
+	seq_printf(m, "\n*** Payload Info ***\n");
+	seq_printf(m, "|   idx   |  state  |  start slot  | # slots |\n");
+	for (i = 0; i < mgr->max_payloads; i++) {
+		seq_printf(m, "%10d%10d%15d%10d\n",
+			   i,
+			   mgr->payloads[i].payload_state,
+			   mgr->payloads[i].start_slot,
+			   mgr->payloads[i].num_slots);
+	}
+	mutex_unlock(&mgr->payload_lock);
+
+	seq_printf(m, "\n*** DPCD Info ***\n");
+	mutex_lock(&mgr->lock);
+	if (mgr->mst_primary) {
+		u8 buf[DP_PAYLOAD_TABLE_SIZE];
+		int ret;
+
+		ret = drm_dp_dpcd_read(mgr->aux, DP_DPCD_REV, buf, DP_RECEIVER_CAP_SIZE);
+		if (ret) {
+			seq_printf(m, "dpcd read failed\n");
+			goto out;
+		}
+		seq_printf(m, "dpcd: %*ph\n", DP_RECEIVER_CAP_SIZE, buf);
+
+		ret = drm_dp_dpcd_read(mgr->aux, DP_FAUX_CAP, buf, 2);
+		if (ret) {
+			seq_printf(m, "faux/mst read failed\n");
+			goto out;
+		}
+		seq_printf(m, "faux/mst: %*ph\n", 2, buf);
+
+		ret = drm_dp_dpcd_read(mgr->aux, DP_MSTM_CTRL, buf, 1);
+		if (ret) {
+			seq_printf(m, "mst ctrl read failed\n");
+			goto out;
+		}
+		seq_printf(m, "mst ctrl: %*ph\n", 1, buf);
+
+		/* dump the standard OUI branch header */
+		ret = drm_dp_dpcd_read(mgr->aux, DP_BRANCH_OUI, buf, DP_BRANCH_OUI_HEADER_SIZE);
+		if (ret) {
+			seq_printf(m, "branch oui read failed\n");
+			goto out;
+		}
+		seq_printf(m, "branch oui: %*phN devid: ", 3, buf);
+
+		for (i = 0x3; i < 0x8 && buf[i]; i++)
+			seq_printf(m, "%c", buf[i]);
+		seq_printf(m, " revision: hw: %x.%x sw: %x.%x\n",
+			   buf[0x9] >> 4, buf[0x9] & 0xf, buf[0xa], buf[0xb]);
+		if (dump_dp_payload_table(mgr, buf))
+			seq_printf(m, "payload table: %*ph\n", DP_PAYLOAD_TABLE_SIZE, buf);
+	}
+
+out:
+	mutex_unlock(&mgr->lock);
+
+}
+EXPORT_SYMBOL(drm_dp_mst_dump_topology);
+
+static void drm_dp_tx_work(struct work_struct *work)
+{
+	struct drm_dp_mst_topology_mgr *mgr = container_of(work, struct drm_dp_mst_topology_mgr, tx_work);
+
+	mutex_lock(&mgr->qlock);
+	if (!list_empty(&mgr->tx_msg_downq))
+		process_single_down_tx_qlock(mgr);
+	mutex_unlock(&mgr->qlock);
+}
+
+static inline void
+drm_dp_delayed_destroy_port(struct drm_dp_mst_port *port)
+{
+	drm_dp_port_set_pdt(port, DP_PEER_DEVICE_NONE, port->mcs);
+
+	if (port->connector) {
+		drm_connector_unregister(port->connector);
+		drm_connector_put(port->connector);
+	}
+
+	drm_dp_mst_put_port_malloc(port);
+}
+
+static inline void
+drm_dp_delayed_destroy_mstb(struct drm_dp_mst_branch *mstb)
+{
+	struct drm_dp_mst_topology_mgr *mgr = mstb->mgr;
+	struct drm_dp_mst_port *port, *port_tmp;
+	struct drm_dp_sideband_msg_tx *txmsg, *txmsg_tmp;
+	bool wake_tx = false;
+
+	mutex_lock(&mgr->lock);
+	list_for_each_entry_safe(port, port_tmp, &mstb->ports, next) {
+		list_del(&port->next);
+		drm_dp_mst_topology_put_port(port);
+	}
+	mutex_unlock(&mgr->lock);
+
+	/* drop any tx slot msg */
+	mutex_lock(&mstb->mgr->qlock);
+	list_for_each_entry_safe(txmsg, txmsg_tmp, &mgr->tx_msg_downq, next) {
+		if (txmsg->dst != mstb)
+			continue;
+
+		txmsg->state = DRM_DP_SIDEBAND_TX_TIMEOUT;
+		list_del(&txmsg->next);
+		wake_tx = true;
+	}
+	mutex_unlock(&mstb->mgr->qlock);
+
+	if (wake_tx)
+		wake_up_all(&mstb->mgr->tx_waitq);
+
+	drm_dp_mst_put_mstb_malloc(mstb);
+}
+
+static void drm_dp_delayed_destroy_work(struct work_struct *work)
+{
+	struct drm_dp_mst_topology_mgr *mgr =
+		container_of(work, struct drm_dp_mst_topology_mgr,
+			     delayed_destroy_work);
+	bool send_hotplug = false, go_again;
+
+	/*
+	 * Not a regular list traverse as we have to drop the destroy
+	 * connector lock before destroying the mstb/port, to avoid AB->BA
+	 * ordering between this lock and the config mutex.
+	 */
+	do {
+		go_again = false;
+
+		for (;;) {
+			struct drm_dp_mst_branch *mstb;
+
+			mutex_lock(&mgr->delayed_destroy_lock);
+			mstb = list_first_entry_or_null(&mgr->destroy_branch_device_list,
+							struct drm_dp_mst_branch,
+							destroy_next);
+			if (mstb)
+				list_del(&mstb->destroy_next);
+			mutex_unlock(&mgr->delayed_destroy_lock);
+
+			if (!mstb)
+				break;
+
+			drm_dp_delayed_destroy_mstb(mstb);
+			go_again = true;
+		}
+
+		for (;;) {
+			struct drm_dp_mst_port *port;
+
+			mutex_lock(&mgr->delayed_destroy_lock);
+			port = list_first_entry_or_null(&mgr->destroy_port_list,
+							struct drm_dp_mst_port,
+							next);
+			if (port)
+				list_del(&port->next);
+			mutex_unlock(&mgr->delayed_destroy_lock);
+
+			if (!port)
+				break;
+
+			drm_dp_delayed_destroy_port(port);
+			send_hotplug = true;
+			go_again = true;
+		}
+	} while (go_again);
+
+	if (send_hotplug)
+		drm_kms_helper_hotplug_event(mgr->dev);
+}
+
+static struct drm_private_state *
+drm_dp_mst_duplicate_state(struct drm_private_obj *obj)
+{
+	struct drm_dp_mst_topology_state *state, *old_state =
+		to_dp_mst_topology_state(obj->state);
+	struct drm_dp_vcpi_allocation *pos, *vcpi;
+
+	state = kmemdup(old_state, sizeof(*state), GFP_KERNEL);
+	if (!state)
+		return NULL;
+
+	__drm_atomic_helper_private_obj_duplicate_state(obj, &state->base);
+
+	INIT_LIST_HEAD(&state->vcpis);
+
+	list_for_each_entry(pos, &old_state->vcpis, next) {
+		/* Prune leftover freed VCPI allocations */
+		if (!pos->vcpi)
+			continue;
+
+		vcpi = kmemdup(pos, sizeof(*vcpi), GFP_KERNEL);
+		if (!vcpi)
+			goto fail;
+
+		drm_dp_mst_get_port_malloc(vcpi->port);
+		list_add(&vcpi->next, &state->vcpis);
+	}
+
+	return &state->base;
+
+fail:
+	list_for_each_entry_safe(pos, vcpi, &state->vcpis, next) {
+		drm_dp_mst_put_port_malloc(pos->port);
+		kfree(pos);
+	}
+	kfree(state);
+
+	return NULL;
+}
+
+static void drm_dp_mst_destroy_state(struct drm_private_obj *obj,
+				     struct drm_private_state *state)
+{
+	struct drm_dp_mst_topology_state *mst_state =
+		to_dp_mst_topology_state(state);
+	struct drm_dp_vcpi_allocation *pos, *tmp;
+
+	list_for_each_entry_safe(pos, tmp, &mst_state->vcpis, next) {
+		/* We only keep references to ports with non-zero VCPIs */
+		if (pos->vcpi)
+			drm_dp_mst_put_port_malloc(pos->port);
+		kfree(pos);
+	}
+
+	kfree(mst_state);
+}
+
+static bool drm_dp_mst_port_downstream_of_branch(struct drm_dp_mst_port *port,
+						 struct drm_dp_mst_branch *branch)
+{
+	while (port->parent) {
+		if (port->parent == branch)
+			return true;
+
+		if (port->parent->port_parent)
+			port = port->parent->port_parent;
+		else
+			break;
+	}
+	return false;
+}
+
+static int
+drm_dp_mst_atomic_check_port_bw_limit(struct drm_dp_mst_port *port,
+				      struct drm_dp_mst_topology_state *state);
+
+static int
+drm_dp_mst_atomic_check_mstb_bw_limit(struct drm_dp_mst_branch *mstb,
+				      struct drm_dp_mst_topology_state *state)
+{
+	struct drm_dp_vcpi_allocation *vcpi;
+	struct drm_dp_mst_port *port;
+	int pbn_used = 0, ret;
+	bool found = false;
+
+	/* Check that we have at least one port in our state that's downstream
+	 * of this branch, otherwise we can skip this branch
+	 */
+	list_for_each_entry(vcpi, &state->vcpis, next) {
+		if (!vcpi->pbn ||
+		    !drm_dp_mst_port_downstream_of_branch(vcpi->port, mstb))
+			continue;
+
+		found = true;
+		break;
+	}
+	if (!found)
+		return 0;
+
+	if (mstb->port_parent)
+		drm_dbg_atomic(mstb->mgr->dev,
+			       "[MSTB:%p] [MST PORT:%p] Checking bandwidth limits on [MSTB:%p]\n",
+			       mstb->port_parent->parent, mstb->port_parent, mstb);
+	else
+		drm_dbg_atomic(mstb->mgr->dev, "[MSTB:%p] Checking bandwidth limits\n", mstb);
+
+	list_for_each_entry(port, &mstb->ports, next) {
+		ret = drm_dp_mst_atomic_check_port_bw_limit(port, state);
+		if (ret < 0)
+			return ret;
+
+		pbn_used += ret;
+	}
+
+	return pbn_used;
+}
+
+static int
+drm_dp_mst_atomic_check_port_bw_limit(struct drm_dp_mst_port *port,
+				      struct drm_dp_mst_topology_state *state)
+{
+	struct drm_dp_vcpi_allocation *vcpi;
+	int pbn_used = 0;
+
+	if (port->pdt == DP_PEER_DEVICE_NONE)
+		return 0;
+
+	if (drm_dp_mst_is_end_device(port->pdt, port->mcs)) {
+		bool found = false;
+
+		list_for_each_entry(vcpi, &state->vcpis, next) {
+			if (vcpi->port != port)
+				continue;
+			if (!vcpi->pbn)
+				return 0;
+
+			found = true;
+			break;
+		}
+		if (!found)
+			return 0;
+
+		/*
+		 * This could happen if the sink deasserted its HPD line, but
+		 * the branch device still reports it as attached (PDT != NONE).
+		 */
+		if (!port->full_pbn) {
+			drm_dbg_atomic(port->mgr->dev,
+				       "[MSTB:%p] [MST PORT:%p] no BW available for the port\n",
+				       port->parent, port);
+			return -EINVAL;
+		}
+
+		pbn_used = vcpi->pbn;
+	} else {
+		pbn_used = drm_dp_mst_atomic_check_mstb_bw_limit(port->mstb,
+								 state);
+		if (pbn_used <= 0)
+			return pbn_used;
+	}
+
+	if (pbn_used > port->full_pbn) {
+		drm_dbg_atomic(port->mgr->dev,
+			       "[MSTB:%p] [MST PORT:%p] required PBN of %d exceeds port limit of %d\n",
+			       port->parent, port, pbn_used, port->full_pbn);
+		return -ENOSPC;
+	}
+
+	drm_dbg_atomic(port->mgr->dev, "[MSTB:%p] [MST PORT:%p] uses %d out of %d PBN\n",
+		       port->parent, port, pbn_used, port->full_pbn);
+
+	return pbn_used;
+}
+
+static inline int
+drm_dp_mst_atomic_check_vcpi_alloc_limit(struct drm_dp_mst_topology_mgr *mgr,
+					 struct drm_dp_mst_topology_state *mst_state)
+{
+	struct drm_dp_vcpi_allocation *vcpi;
+	int avail_slots = mst_state->total_avail_slots, payload_count = 0;
+
+	list_for_each_entry(vcpi, &mst_state->vcpis, next) {
+		/* Releasing VCPI is always OK-even if the port is gone */
+		if (!vcpi->vcpi) {
+			drm_dbg_atomic(mgr->dev, "[MST PORT:%p] releases all VCPI slots\n",
+				       vcpi->port);
+			continue;
+		}
+
+		drm_dbg_atomic(mgr->dev, "[MST PORT:%p] requires %d vcpi slots\n",
+			       vcpi->port, vcpi->vcpi);
+
+		avail_slots -= vcpi->vcpi;
+		if (avail_slots < 0) {
+			drm_dbg_atomic(mgr->dev,
+				       "[MST PORT:%p] not enough VCPI slots in mst state %p (avail=%d)\n",
+				       vcpi->port, mst_state, avail_slots + vcpi->vcpi);
+			return -ENOSPC;
+		}
+
+		if (++payload_count > mgr->max_payloads) {
+			drm_dbg_atomic(mgr->dev,
+				       "[MST MGR:%p] state %p has too many payloads (max=%d)\n",
+				       mgr, mst_state, mgr->max_payloads);
+			return -EINVAL;
+		}
+	}
+	drm_dbg_atomic(mgr->dev, "[MST MGR:%p] mst state %p VCPI avail=%d used=%d\n",
+		       mgr, mst_state, avail_slots, mst_state->total_avail_slots - avail_slots);
+
+	return 0;
+}
+
+/**
+ * drm_dp_mst_add_affected_dsc_crtcs
+ * @state: Pointer to the new struct drm_dp_mst_topology_state
+ * @mgr: MST topology manager
+ *
+ * Whenever there is a change in mst topology
+ * DSC configuration would have to be recalculated
+ * therefore we need to trigger modeset on all affected
+ * CRTCs in that topology
+ *
+ * See also:
+ * drm_dp_mst_atomic_enable_dsc()
+ */
+int drm_dp_mst_add_affected_dsc_crtcs(struct drm_atomic_state *state, struct drm_dp_mst_topology_mgr *mgr)
+{
+	struct drm_dp_mst_topology_state *mst_state;
+	struct drm_dp_vcpi_allocation *pos;
+	struct drm_connector *connector;
+	struct drm_connector_state *conn_state;
+	struct drm_crtc *crtc;
+	struct drm_crtc_state *crtc_state;
+
+	mst_state = drm_atomic_get_mst_topology_state(state, mgr);
+
+	if (IS_ERR(mst_state))
+		return -EINVAL;
+
+	list_for_each_entry(pos, &mst_state->vcpis, next) {
+
+		connector = pos->port->connector;
+
+		if (!connector)
+			return -EINVAL;
+
+		conn_state = drm_atomic_get_connector_state(state, connector);
+
+		if (IS_ERR(conn_state))
+			return PTR_ERR(conn_state);
+
+		crtc = conn_state->crtc;
+
+		if (!crtc)
+			continue;
+
+		if (!drm_dp_mst_dsc_aux_for_port(pos->port))
+			continue;
+
+		crtc_state = drm_atomic_get_crtc_state(mst_state->base.state, crtc);
+
+		if (IS_ERR(crtc_state))
+			return PTR_ERR(crtc_state);
+
+		drm_dbg_atomic(mgr->dev, "[MST MGR:%p] Setting mode_changed flag on CRTC %p\n",
+			       mgr, crtc);
+
+		crtc_state->mode_changed = true;
+	}
+	return 0;
+}
+EXPORT_SYMBOL(drm_dp_mst_add_affected_dsc_crtcs);
+
+/**
+ * drm_dp_mst_atomic_enable_dsc - Set DSC Enable Flag to On/Off
+ * @state: Pointer to the new drm_atomic_state
+ * @port: Pointer to the affected MST Port
+ * @pbn: Newly recalculated bw required for link with DSC enabled
+ * @pbn_div: Divider to calculate correct number of pbn per slot
+ * @enable: Boolean flag to enable or disable DSC on the port
+ *
+ * This function enables DSC on the given Port
+ * by recalculating its vcpi from pbn provided
+ * and sets dsc_enable flag to keep track of which
+ * ports have DSC enabled
+ *
+ */
+int drm_dp_mst_atomic_enable_dsc(struct drm_atomic_state *state,
+				 struct drm_dp_mst_port *port,
+				 int pbn, int pbn_div,
+				 bool enable)
+{
+	struct drm_dp_mst_topology_state *mst_state;
+	struct drm_dp_vcpi_allocation *pos;
+	bool found = false;
+	int vcpi = 0;
+
+	mst_state = drm_atomic_get_mst_topology_state(state, port->mgr);
+
+	if (IS_ERR(mst_state))
+		return PTR_ERR(mst_state);
+
+	list_for_each_entry(pos, &mst_state->vcpis, next) {
+		if (pos->port == port) {
+			found = true;
+			break;
+		}
+	}
+
+	if (!found) {
+		drm_dbg_atomic(state->dev,
+			       "[MST PORT:%p] Couldn't find VCPI allocation in mst state %p\n",
+			       port, mst_state);
+		return -EINVAL;
+	}
+
+	if (pos->dsc_enabled == enable) {
+		drm_dbg_atomic(state->dev,
+			       "[MST PORT:%p] DSC flag is already set to %d, returning %d VCPI slots\n",
+			       port, enable, pos->vcpi);
+		vcpi = pos->vcpi;
+	}
+
+	if (enable) {
+		vcpi = drm_dp_atomic_find_vcpi_slots(state, port->mgr, port, pbn, pbn_div);
+		drm_dbg_atomic(state->dev,
+			       "[MST PORT:%p] Enabling DSC flag, reallocating %d VCPI slots on the port\n",
+			       port, vcpi);
+		if (vcpi < 0)
+			return -EINVAL;
+	}
+
+	pos->dsc_enabled = enable;
+
+	return vcpi;
+}
+EXPORT_SYMBOL(drm_dp_mst_atomic_enable_dsc);
+/**
+ * drm_dp_mst_atomic_check - Check that the new state of an MST topology in an
+ * atomic update is valid
+ * @state: Pointer to the new &struct drm_dp_mst_topology_state
+ *
+ * Checks the given topology state for an atomic update to ensure that it's
+ * valid. This includes checking whether there's enough bandwidth to support
+ * the new VCPI allocations in the atomic update.
+ *
+ * Any atomic drivers supporting DP MST must make sure to call this after
+ * checking the rest of their state in their
+ * &drm_mode_config_funcs.atomic_check() callback.
+ *
+ * See also:
+ * drm_dp_atomic_find_vcpi_slots()
+ * drm_dp_atomic_release_vcpi_slots()
+ *
+ * Returns:
+ *
+ * 0 if the new state is valid, negative error code otherwise.
+ */
+int drm_dp_mst_atomic_check(struct drm_atomic_state *state)
+{
+	struct drm_dp_mst_topology_mgr *mgr;
+	struct drm_dp_mst_topology_state *mst_state;
+	int i, ret = 0;
+
+	for_each_new_mst_mgr_in_state(state, mgr, mst_state, i) {
+		if (!mgr->mst_state)
+			continue;
+
+		ret = drm_dp_mst_atomic_check_vcpi_alloc_limit(mgr, mst_state);
+		if (ret)
+			break;
+
+		mutex_lock(&mgr->lock);
+		ret = drm_dp_mst_atomic_check_mstb_bw_limit(mgr->mst_primary,
+							    mst_state);
+		mutex_unlock(&mgr->lock);
+		if (ret < 0)
+			break;
+		else
+			ret = 0;
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL(drm_dp_mst_atomic_check);
+
+const struct drm_private_state_funcs drm_dp_mst_topology_state_funcs = {
+	.atomic_duplicate_state = drm_dp_mst_duplicate_state,
+	.atomic_destroy_state = drm_dp_mst_destroy_state,
+};
+EXPORT_SYMBOL(drm_dp_mst_topology_state_funcs);
+
+/**
+ * drm_atomic_get_mst_topology_state: get MST topology state
+ *
+ * @state: global atomic state
+ * @mgr: MST topology manager, also the private object in this case
+ *
+ * This function wraps drm_atomic_get_priv_obj_state() passing in the MST atomic
+ * state vtable so that the private object state returned is that of a MST
+ * topology object. Also, drm_atomic_get_private_obj_state() expects the caller
+ * to care of the locking, so warn if don't hold the connection_mutex.
+ *
+ * RETURNS:
+ *
+ * The MST topology state or error pointer.
+ */
+struct drm_dp_mst_topology_state *drm_atomic_get_mst_topology_state(struct drm_atomic_state *state,
+								    struct drm_dp_mst_topology_mgr *mgr)
+{
+	return to_dp_mst_topology_state(drm_atomic_get_private_obj_state(state, &mgr->base));
+}
+EXPORT_SYMBOL(drm_atomic_get_mst_topology_state);
+
+/**
+ * drm_dp_mst_topology_mgr_init - initialise a topology manager
+ * @mgr: manager struct to initialise
+ * @dev: device providing this structure - for i2c addition.
+ * @aux: DP helper aux channel to talk to this device
+ * @max_dpcd_transaction_bytes: hw specific DPCD transaction limit
+ * @max_payloads: maximum number of payloads this GPU can source
+ * @max_lane_count: maximum number of lanes this GPU supports
+ * @max_link_rate: maximum link rate per lane this GPU supports in kHz
+ * @conn_base_id: the connector object ID the MST device is connected to.
+ *
+ * Return 0 for success, or negative error code on failure
+ */
+int drm_dp_mst_topology_mgr_init(struct drm_dp_mst_topology_mgr *mgr,
+				 struct drm_device *dev, struct drm_dp_aux *aux,
+				 int max_dpcd_transaction_bytes, int max_payloads,
+				 int max_lane_count, int max_link_rate,
+				 int conn_base_id)
+{
+	struct drm_dp_mst_topology_state *mst_state;
+
+	mutex_init(&mgr->lock);
+	mutex_init(&mgr->qlock);
+	mutex_init(&mgr->payload_lock);
+	mutex_init(&mgr->delayed_destroy_lock);
+	mutex_init(&mgr->up_req_lock);
+	mutex_init(&mgr->probe_lock);
+#if IS_ENABLED(CONFIG_DRM_DEBUG_DP_MST_TOPOLOGY_REFS)
+	mutex_init(&mgr->topology_ref_history_lock);
+#endif
+	INIT_LIST_HEAD(&mgr->tx_msg_downq);
+	INIT_LIST_HEAD(&mgr->destroy_port_list);
+	INIT_LIST_HEAD(&mgr->destroy_branch_device_list);
+	INIT_LIST_HEAD(&mgr->up_req_list);
+
+	/*
+	 * delayed_destroy_work will be queued on a dedicated WQ, so that any
+	 * requeuing will be also flushed when deiniting the topology manager.
+	 */
+	mgr->delayed_destroy_wq = alloc_ordered_workqueue("drm_dp_mst_wq", 0);
+	if (mgr->delayed_destroy_wq == NULL)
+		return -ENOMEM;
+
+	INIT_WORK(&mgr->work, drm_dp_mst_link_probe_work);
+	INIT_WORK(&mgr->tx_work, drm_dp_tx_work);
+	INIT_WORK(&mgr->delayed_destroy_work, drm_dp_delayed_destroy_work);
+	INIT_WORK(&mgr->up_req_work, drm_dp_mst_up_req_work);
+	init_waitqueue_head(&mgr->tx_waitq);
+	mgr->dev = dev;
+	mgr->aux = aux;
+	mgr->max_dpcd_transaction_bytes = max_dpcd_transaction_bytes;
+	mgr->max_payloads = max_payloads;
+	mgr->max_lane_count = max_lane_count;
+	mgr->max_link_rate = max_link_rate;
+	mgr->conn_base_id = conn_base_id;
+	if (max_payloads + 1 > sizeof(mgr->payload_mask) * 8 ||
+	    max_payloads + 1 > sizeof(mgr->vcpi_mask) * 8)
+		return -EINVAL;
+	mgr->payloads = kcalloc(max_payloads, sizeof(struct drm_dp_payload), GFP_KERNEL);
+	if (!mgr->payloads)
+		return -ENOMEM;
+	mgr->proposed_vcpis = kcalloc(max_payloads, sizeof(struct drm_dp_vcpi *), GFP_KERNEL);
+	if (!mgr->proposed_vcpis)
+		return -ENOMEM;
+	set_bit(0, &mgr->payload_mask);
+
+	mst_state = kzalloc(sizeof(*mst_state), GFP_KERNEL);
+	if (mst_state == NULL)
+		return -ENOMEM;
+
+	mst_state->total_avail_slots = 63;
+	mst_state->start_slot = 1;
+
+	mst_state->mgr = mgr;
+	INIT_LIST_HEAD(&mst_state->vcpis);
+
+	drm_atomic_private_obj_init(dev, &mgr->base,
+				    &mst_state->base,
+				    &drm_dp_mst_topology_state_funcs);
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_dp_mst_topology_mgr_init);
+
+/**
+ * drm_dp_mst_topology_mgr_destroy() - destroy topology manager.
+ * @mgr: manager to destroy
+ */
+void drm_dp_mst_topology_mgr_destroy(struct drm_dp_mst_topology_mgr *mgr)
+{
+	drm_dp_mst_topology_mgr_set_mst(mgr, false);
+	flush_work(&mgr->work);
+	/* The following will also drain any requeued work on the WQ. */
+	if (mgr->delayed_destroy_wq) {
+		destroy_workqueue(mgr->delayed_destroy_wq);
+		mgr->delayed_destroy_wq = NULL;
+	}
+	mutex_lock(&mgr->payload_lock);
+	kfree(mgr->payloads);
+	mgr->payloads = NULL;
+	kfree(mgr->proposed_vcpis);
+	mgr->proposed_vcpis = NULL;
+	mutex_unlock(&mgr->payload_lock);
+	mgr->dev = NULL;
+	mgr->aux = NULL;
+	drm_atomic_private_obj_fini(&mgr->base);
+	mgr->funcs = NULL;
+
+	mutex_destroy(&mgr->delayed_destroy_lock);
+	mutex_destroy(&mgr->payload_lock);
+	mutex_destroy(&mgr->qlock);
+	mutex_destroy(&mgr->lock);
+	mutex_destroy(&mgr->up_req_lock);
+	mutex_destroy(&mgr->probe_lock);
+#if IS_ENABLED(CONFIG_DRM_DEBUG_DP_MST_TOPOLOGY_REFS)
+	mutex_destroy(&mgr->topology_ref_history_lock);
+#endif
+}
+EXPORT_SYMBOL(drm_dp_mst_topology_mgr_destroy);
+
+static bool remote_i2c_read_ok(const struct i2c_msg msgs[], int num)
+{
+	int i;
+
+	if (num - 1 > DP_REMOTE_I2C_READ_MAX_TRANSACTIONS)
+		return false;
+
+	for (i = 0; i < num - 1; i++) {
+		if (msgs[i].flags & I2C_M_RD ||
+		    msgs[i].len > 0xff)
+			return false;
+	}
+
+	return msgs[num - 1].flags & I2C_M_RD &&
+		msgs[num - 1].len <= 0xff;
+}
+
+static bool remote_i2c_write_ok(const struct i2c_msg msgs[], int num)
+{
+	int i;
+
+	for (i = 0; i < num - 1; i++) {
+		if (msgs[i].flags & I2C_M_RD || !(msgs[i].flags & I2C_M_STOP) ||
+		    msgs[i].len > 0xff)
+			return false;
+	}
+
+	return !(msgs[num - 1].flags & I2C_M_RD) && msgs[num - 1].len <= 0xff;
+}
+
+static int drm_dp_mst_i2c_read(struct drm_dp_mst_branch *mstb,
+			       struct drm_dp_mst_port *port,
+			       struct i2c_msg *msgs, int num)
+{
+	struct drm_dp_mst_topology_mgr *mgr = port->mgr;
+	unsigned int i;
+	struct drm_dp_sideband_msg_req_body msg;
+	struct drm_dp_sideband_msg_tx *txmsg = NULL;
+	int ret;
+
+	memset(&msg, 0, sizeof(msg));
+	msg.req_type = DP_REMOTE_I2C_READ;
+	msg.u.i2c_read.num_transactions = num - 1;
+	msg.u.i2c_read.port_number = port->port_num;
+	for (i = 0; i < num - 1; i++) {
+		msg.u.i2c_read.transactions[i].i2c_dev_id = msgs[i].addr;
+		msg.u.i2c_read.transactions[i].num_bytes = msgs[i].len;
+		msg.u.i2c_read.transactions[i].bytes = msgs[i].buf;
+		msg.u.i2c_read.transactions[i].no_stop_bit = !(msgs[i].flags & I2C_M_STOP);
+	}
+	msg.u.i2c_read.read_i2c_device_id = msgs[num - 1].addr;
+	msg.u.i2c_read.num_bytes_read = msgs[num - 1].len;
+
+	txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
+	if (!txmsg) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	txmsg->dst = mstb;
+	drm_dp_encode_sideband_req(&msg, txmsg);
+
+	drm_dp_queue_down_tx(mgr, txmsg);
+
+	ret = drm_dp_mst_wait_tx_reply(mstb, txmsg);
+	if (ret > 0) {
+
+		if (txmsg->reply.reply_type == DP_SIDEBAND_REPLY_NAK) {
+			ret = -EREMOTEIO;
+			goto out;
+		}
+		if (txmsg->reply.u.remote_i2c_read_ack.num_bytes != msgs[num - 1].len) {
+			ret = -EIO;
+			goto out;
+		}
+		memcpy(msgs[num - 1].buf, txmsg->reply.u.remote_i2c_read_ack.bytes, msgs[num - 1].len);
+		ret = num;
+	}
+out:
+	kfree(txmsg);
+	return ret;
+}
+
+static int drm_dp_mst_i2c_write(struct drm_dp_mst_branch *mstb,
+				struct drm_dp_mst_port *port,
+				struct i2c_msg *msgs, int num)
+{
+	struct drm_dp_mst_topology_mgr *mgr = port->mgr;
+	unsigned int i;
+	struct drm_dp_sideband_msg_req_body msg;
+	struct drm_dp_sideband_msg_tx *txmsg = NULL;
+	int ret;
+
+	txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
+	if (!txmsg) {
+		ret = -ENOMEM;
+		goto out;
+	}
+	for (i = 0; i < num; i++) {
+		memset(&msg, 0, sizeof(msg));
+		msg.req_type = DP_REMOTE_I2C_WRITE;
+		msg.u.i2c_write.port_number = port->port_num;
+		msg.u.i2c_write.write_i2c_device_id = msgs[i].addr;
+		msg.u.i2c_write.num_bytes = msgs[i].len;
+		msg.u.i2c_write.bytes = msgs[i].buf;
+
+		memset(txmsg, 0, sizeof(*txmsg));
+		txmsg->dst = mstb;
+
+		drm_dp_encode_sideband_req(&msg, txmsg);
+		drm_dp_queue_down_tx(mgr, txmsg);
+
+		ret = drm_dp_mst_wait_tx_reply(mstb, txmsg);
+		if (ret > 0) {
+			if (txmsg->reply.reply_type == DP_SIDEBAND_REPLY_NAK) {
+				ret = -EREMOTEIO;
+				goto out;
+			}
+		} else {
+			goto out;
+		}
+	}
+	ret = num;
+out:
+	kfree(txmsg);
+	return ret;
+}
+
+/* I2C device */
+static int drm_dp_mst_i2c_xfer(struct i2c_adapter *adapter,
+			       struct i2c_msg *msgs, int num)
+{
+	struct drm_dp_aux *aux = adapter->algo_data;
+	struct drm_dp_mst_port *port =
+		container_of(aux, struct drm_dp_mst_port, aux);
+	struct drm_dp_mst_branch *mstb;
+	struct drm_dp_mst_topology_mgr *mgr = port->mgr;
+	int ret;
+
+	mstb = drm_dp_mst_topology_get_mstb_validated(mgr, port->parent);
+	if (!mstb)
+		return -EREMOTEIO;
+
+	if (remote_i2c_read_ok(msgs, num)) {
+		ret = drm_dp_mst_i2c_read(mstb, port, msgs, num);
+	} else if (remote_i2c_write_ok(msgs, num)) {
+		ret = drm_dp_mst_i2c_write(mstb, port, msgs, num);
+	} else {
+		drm_dbg_kms(mgr->dev, "Unsupported I2C transaction for MST device\n");
+		ret = -EIO;
+	}
+
+	drm_dp_mst_topology_put_mstb(mstb);
+	return ret;
+}
+
+static u32 drm_dp_mst_i2c_functionality(struct i2c_adapter *adapter)
+{
+	return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL |
+	       I2C_FUNC_SMBUS_READ_BLOCK_DATA |
+	       I2C_FUNC_SMBUS_BLOCK_PROC_CALL |
+	       I2C_FUNC_10BIT_ADDR;
+}
+
+static const struct i2c_algorithm drm_dp_mst_i2c_algo = {
+	.functionality = drm_dp_mst_i2c_functionality,
+	.master_xfer = drm_dp_mst_i2c_xfer,
+};
+
+/**
+ * drm_dp_mst_register_i2c_bus() - register an I2C adapter for I2C-over-AUX
+ * @port: The port to add the I2C bus on
+ *
+ * Returns 0 on success or a negative error code on failure.
+ */
+static int drm_dp_mst_register_i2c_bus(struct drm_dp_mst_port *port)
+{
+	struct drm_dp_aux *aux = &port->aux;
+	struct device *parent_dev = port->mgr->dev->dev;
+
+	aux->ddc.algo = &drm_dp_mst_i2c_algo;
+	aux->ddc.algo_data = aux;
+	aux->ddc.retries = 3;
+
+	aux->ddc.class = I2C_CLASS_DDC;
+	aux->ddc.owner = THIS_MODULE;
+	/* FIXME: set the kdev of the port's connector as parent */
+	aux->ddc.dev.parent = parent_dev;
+	aux->ddc.dev.of_node = parent_dev->of_node;
+
+	strlcpy(aux->ddc.name, aux->name ? aux->name : dev_name(parent_dev),
+		sizeof(aux->ddc.name));
+
+	return i2c_add_adapter(&aux->ddc);
+}
+
+/**
+ * drm_dp_mst_unregister_i2c_bus() - unregister an I2C-over-AUX adapter
+ * @port: The port to remove the I2C bus from
+ */
+static void drm_dp_mst_unregister_i2c_bus(struct drm_dp_mst_port *port)
+{
+	i2c_del_adapter(&port->aux.ddc);
+}
+
+/**
+ * drm_dp_mst_is_virtual_dpcd() - Is the given port a virtual DP Peer Device
+ * @port: The port to check
+ *
+ * A single physical MST hub object can be represented in the topology
+ * by multiple branches, with virtual ports between those branches.
+ *
+ * As of DP1.4, An MST hub with internal (virtual) ports must expose
+ * certain DPCD registers over those ports. See sections 2.6.1.1.1
+ * and 2.6.1.1.2 of Display Port specification v1.4 for details.
+ *
+ * May acquire mgr->lock
+ *
+ * Returns:
+ * true if the port is a virtual DP peer device, false otherwise
+ */
+static bool drm_dp_mst_is_virtual_dpcd(struct drm_dp_mst_port *port)
+{
+	struct drm_dp_mst_port *downstream_port;
+
+	if (!port || port->dpcd_rev < DP_DPCD_REV_14)
+		return false;
+
+	/* Virtual DP Sink (Internal Display Panel) */
+	if (port->port_num >= 8)
+		return true;
+
+	/* DP-to-HDMI Protocol Converter */
+	if (port->pdt == DP_PEER_DEVICE_DP_LEGACY_CONV &&
+	    !port->mcs &&
+	    port->ldps)
+		return true;
+
+	/* DP-to-DP */
+	mutex_lock(&port->mgr->lock);
+	if (port->pdt == DP_PEER_DEVICE_MST_BRANCHING &&
+	    port->mstb &&
+	    port->mstb->num_ports == 2) {
+		list_for_each_entry(downstream_port, &port->mstb->ports, next) {
+			if (downstream_port->pdt == DP_PEER_DEVICE_SST_SINK &&
+			    !downstream_port->input) {
+				mutex_unlock(&port->mgr->lock);
+				return true;
+			}
+		}
+	}
+	mutex_unlock(&port->mgr->lock);
+
+	return false;
+}
+
+/**
+ * drm_dp_mst_dsc_aux_for_port() - Find the correct aux for DSC
+ * @port: The port to check. A leaf of the MST tree with an attached display.
+ *
+ * Depending on the situation, DSC may be enabled via the endpoint aux,
+ * the immediately upstream aux, or the connector's physical aux.
+ *
+ * This is both the correct aux to read DSC_CAPABILITY and the
+ * correct aux to write DSC_ENABLED.
+ *
+ * This operation can be expensive (up to four aux reads), so
+ * the caller should cache the return.
+ *
+ * Returns:
+ * NULL if DSC cannot be enabled on this port, otherwise the aux device
+ */
+struct drm_dp_aux *drm_dp_mst_dsc_aux_for_port(struct drm_dp_mst_port *port)
+{
+	struct drm_dp_mst_port *immediate_upstream_port;
+	struct drm_dp_mst_port *fec_port;
+	struct drm_dp_desc desc = {};
+	u8 endpoint_fec;
+	u8 endpoint_dsc;
+
+	if (!port)
+		return NULL;
+
+	if (port->parent->port_parent)
+		immediate_upstream_port = port->parent->port_parent;
+	else
+		immediate_upstream_port = NULL;
+
+	fec_port = immediate_upstream_port;
+	while (fec_port) {
+		/*
+		 * Each physical link (i.e. not a virtual port) between the
+		 * output and the primary device must support FEC
+		 */
+		if (!drm_dp_mst_is_virtual_dpcd(fec_port) &&
+		    !fec_port->fec_capable)
+			return NULL;
+
+		fec_port = fec_port->parent->port_parent;
+	}
+
+	/* DP-to-DP peer device */
+	if (drm_dp_mst_is_virtual_dpcd(immediate_upstream_port)) {
+		u8 upstream_dsc;
+
+		if (drm_dp_dpcd_read(&port->aux,
+				     DP_DSC_SUPPORT, &endpoint_dsc, 1) != 1)
+			return NULL;
+		if (drm_dp_dpcd_read(&port->aux,
+				     DP_FEC_CAPABILITY, &endpoint_fec, 1) != 1)
+			return NULL;
+		if (drm_dp_dpcd_read(&immediate_upstream_port->aux,
+				     DP_DSC_SUPPORT, &upstream_dsc, 1) != 1)
+			return NULL;
+
+		/* Enpoint decompression with DP-to-DP peer device */
+		if ((endpoint_dsc & DP_DSC_DECOMPRESSION_IS_SUPPORTED) &&
+		    (endpoint_fec & DP_FEC_CAPABLE) &&
+		    (upstream_dsc & 0x2) /* DSC passthrough */)
+			return &port->aux;
+
+		/* Virtual DPCD decompression with DP-to-DP peer device */
+		return &immediate_upstream_port->aux;
+	}
+
+	/* Virtual DPCD decompression with DP-to-HDMI or Virtual DP Sink */
+	if (drm_dp_mst_is_virtual_dpcd(port))
+		return &port->aux;
+
+	/*
+	 * Synaptics quirk
+	 * Applies to ports for which:
+	 * - Physical aux has Synaptics OUI
+	 * - DPv1.4 or higher
+	 * - Port is on primary branch device
+	 * - Not a VGA adapter (DP_DWN_STRM_PORT_TYPE_ANALOG)
+	 */
+	if (drm_dp_read_desc(port->mgr->aux, &desc, true))
+		return NULL;
+
+	if (drm_dp_has_quirk(&desc, DP_DPCD_QUIRK_DSC_WITHOUT_VIRTUAL_DPCD) &&
+	    port->mgr->dpcd[DP_DPCD_REV] >= DP_DPCD_REV_14 &&
+	    port->parent == port->mgr->mst_primary) {
+		u8 dpcd_ext[DP_RECEIVER_CAP_SIZE];
+
+		if (drm_dp_read_dpcd_caps(port->mgr->aux, dpcd_ext) < 0)
+			return NULL;
+
+		if ((dpcd_ext[DP_DOWNSTREAMPORT_PRESENT] & DP_DWN_STRM_PORT_PRESENT) &&
+		    ((dpcd_ext[DP_DOWNSTREAMPORT_PRESENT] & DP_DWN_STRM_PORT_TYPE_MASK)
+		     != DP_DWN_STRM_PORT_TYPE_ANALOG))
+			return port->mgr->aux;
+	}
+
+	/*
+	 * The check below verifies if the MST sink
+	 * connected to the GPU is capable of DSC -
+	 * therefore the endpoint needs to be
+	 * both DSC and FEC capable.
+	 */
+	if (drm_dp_dpcd_read(&port->aux,
+	   DP_DSC_SUPPORT, &endpoint_dsc, 1) != 1)
+		return NULL;
+	if (drm_dp_dpcd_read(&port->aux,
+	   DP_FEC_CAPABILITY, &endpoint_fec, 1) != 1)
+		return NULL;
+	if ((endpoint_dsc & DP_DSC_DECOMPRESSION_IS_SUPPORTED) &&
+	   (endpoint_fec & DP_FEC_CAPABLE))
+		return &port->aux;
+
+	return NULL;
+}
+EXPORT_SYMBOL(drm_dp_mst_dsc_aux_for_port);