usb: xhci: Add DbC support in xHCI driver

xHCI compatible USB host controllers(i.e. super-speed USB3 controllers)
can be implemented with the Debug Capability(DbC). It presents a debug
device which is fully compliant with the USB framework and provides the
equivalent of a very high performance full-duplex serial link. The debug
capability operation model and registers interface are defined in 7.6.8
of the xHCI specification, revision 1.1.

The DbC debug device shares a root port with the xHCI host. By default,
the debug capability is disabled and the root port is assigned to xHCI.
When the DbC is enabled, the root port will be assigned to the DbC debug
device, and the xHCI sees nothing on this port. This implementation uses
a sysfs node named <dbc> under the xHCI device to manage the enabling
and disabling of the debug capability.

When the debug capability is enabled, it will present a debug device
through the debug port. This debug device is fully compliant with the
USB3 framework, and it can be enumerated by a debug host on the other
end of the USB link. As soon as the debug device is configured, a TTY
serial device named /dev/ttyDBC0 will be created.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 996 insertions, 0 deletions

diff --git a/drivers/usb/host/xhci-dbgcap.c b/drivers/usb/host/xhci-dbgcap.c
new file mode 100644
index 000000000000..671e5023e683
--- /dev/null
+++ b/drivers/usb/host/xhci-dbgcap.c
@@ -0,0 +1,996 @@
+/**
+ * xhci-dbgcap.c - xHCI debug capability support
+ *
+ * Copyright (C) 2017 Intel Corporation
+ *
+ * Author: Lu Baolu <baolu.lu@linux.intel.com>
+ */
+#include <linux/dma-mapping.h>
+#include <linux/slab.h>
+#include <linux/nls.h>
+
+#include "xhci.h"
+#include "xhci-trace.h"
+#include "xhci-dbgcap.h"
+
+static inline void *
+dbc_dma_alloc_coherent(struct xhci_hcd *xhci, size_t size,
+		       dma_addr_t *dma_handle, gfp_t flags)
+{
+	void		*vaddr;
+
+	vaddr = dma_alloc_coherent(xhci_to_hcd(xhci)->self.sysdev,
+				   size, dma_handle, flags);
+	memset(vaddr, 0, size);
+	return vaddr;
+}
+
+static inline void
+dbc_dma_free_coherent(struct xhci_hcd *xhci, size_t size,
+		      void *cpu_addr, dma_addr_t dma_handle)
+{
+	if (cpu_addr)
+		dma_free_coherent(xhci_to_hcd(xhci)->self.sysdev,
+				  size, cpu_addr, dma_handle);
+}
+
+static u32 xhci_dbc_populate_strings(struct dbc_str_descs *strings)
+{
+	struct usb_string_descriptor	*s_desc;
+	u32				string_length;
+
+	/* Serial string: */
+	s_desc = (struct usb_string_descriptor *)strings->serial;
+	utf8s_to_utf16s(DBC_STRING_SERIAL, strlen(DBC_STRING_SERIAL),
+			UTF16_LITTLE_ENDIAN, (wchar_t *)s_desc->wData,
+			DBC_MAX_STRING_LENGTH);
+
+	s_desc->bLength		= (strlen(DBC_STRING_SERIAL) + 1) * 2;
+	s_desc->bDescriptorType	= USB_DT_STRING;
+	string_length		= s_desc->bLength;
+	string_length		<<= 8;
+
+	/* Product string: */
+	s_desc = (struct usb_string_descriptor *)strings->product;
+	utf8s_to_utf16s(DBC_STRING_PRODUCT, strlen(DBC_STRING_PRODUCT),
+			UTF16_LITTLE_ENDIAN, (wchar_t *)s_desc->wData,
+			DBC_MAX_STRING_LENGTH);
+
+	s_desc->bLength		= (strlen(DBC_STRING_PRODUCT) + 1) * 2;
+	s_desc->bDescriptorType	= USB_DT_STRING;
+	string_length		+= s_desc->bLength;
+	string_length		<<= 8;
+
+	/* Manufacture string: */
+	s_desc = (struct usb_string_descriptor *)strings->manufacturer;
+	utf8s_to_utf16s(DBC_STRING_MANUFACTURER,
+			strlen(DBC_STRING_MANUFACTURER),
+			UTF16_LITTLE_ENDIAN, (wchar_t *)s_desc->wData,
+			DBC_MAX_STRING_LENGTH);
+
+	s_desc->bLength		= (strlen(DBC_STRING_MANUFACTURER) + 1) * 2;
+	s_desc->bDescriptorType	= USB_DT_STRING;
+	string_length		+= s_desc->bLength;
+	string_length		<<= 8;
+
+	/* String0: */
+	strings->string0[0]	= 4;
+	strings->string0[1]	= USB_DT_STRING;
+	strings->string0[2]	= 0x09;
+	strings->string0[3]	= 0x04;
+	string_length		+= 4;
+
+	return string_length;
+}
+
+static void xhci_dbc_init_contexts(struct xhci_hcd *xhci, u32 string_length)
+{
+	struct xhci_dbc		*dbc;
+	struct dbc_info_context	*info;
+	struct xhci_ep_ctx	*ep_ctx;
+	u32			dev_info;
+	dma_addr_t		deq, dma;
+	unsigned int		max_burst;
+
+	dbc = xhci->dbc;
+	if (!dbc)
+		return;
+
+	/* Populate info Context: */
+	info			= (struct dbc_info_context *)dbc->ctx->bytes;
+	dma			= dbc->string_dma;
+	info->string0		= cpu_to_le64(dma);
+	info->manufacturer	= cpu_to_le64(dma + DBC_MAX_STRING_LENGTH);
+	info->product		= cpu_to_le64(dma + DBC_MAX_STRING_LENGTH * 2);
+	info->serial		= cpu_to_le64(dma + DBC_MAX_STRING_LENGTH * 3);
+	info->length		= cpu_to_le32(string_length);
+
+	/* Populate bulk out endpoint context: */
+	ep_ctx			= dbc_bulkout_ctx(dbc);
+	max_burst		= DBC_CTRL_MAXBURST(readl(&dbc->regs->control));
+	deq			= dbc_bulkout_enq(dbc);
+	ep_ctx->ep_info		= 0;
+	ep_ctx->ep_info2	= dbc_epctx_info2(BULK_OUT_EP, 1024, max_burst);
+	ep_ctx->deq		= cpu_to_le64(deq | dbc->ring_out->cycle_state);
+
+	/* Populate bulk in endpoint context: */
+	ep_ctx			= dbc_bulkin_ctx(dbc);
+	deq			= dbc_bulkin_enq(dbc);
+	ep_ctx->ep_info		= 0;
+	ep_ctx->ep_info2	= dbc_epctx_info2(BULK_IN_EP, 1024, max_burst);
+	ep_ctx->deq		= cpu_to_le64(deq | dbc->ring_in->cycle_state);
+
+	/* Set DbC context and info registers: */
+	xhci_write_64(xhci, dbc->ctx->dma, &dbc->regs->dccp);
+
+	dev_info = cpu_to_le32((DBC_VENDOR_ID << 16) | DBC_PROTOCOL);
+	writel(dev_info, &dbc->regs->devinfo1);
+
+	dev_info = cpu_to_le32((DBC_DEVICE_REV << 16) | DBC_PRODUCT_ID);
+	writel(dev_info, &dbc->regs->devinfo2);
+}
+
+static void xhci_dbc_giveback(struct dbc_request *req, int status)
+	__releases(&dbc->lock)
+	__acquires(&dbc->lock)
+{
+	struct dbc_ep		*dep = req->dep;
+	struct xhci_dbc		*dbc = dep->dbc;
+	struct xhci_hcd		*xhci = dbc->xhci;
+	struct device		*dev = xhci_to_hcd(dbc->xhci)->self.sysdev;
+
+	list_del_init(&req->list_pending);
+	req->trb_dma = 0;
+	req->trb = NULL;
+
+	if (req->status == -EINPROGRESS)
+		req->status = status;
+
+	trace_xhci_dbc_giveback_request(req);
+
+	dma_unmap_single(dev,
+			 req->dma,
+			 req->length,
+			 dbc_ep_dma_direction(dep));
+
+	/* Give back the transfer request: */
+	spin_unlock(&dbc->lock);
+	req->complete(xhci, req);
+	spin_lock(&dbc->lock);
+}
+
+static void xhci_dbc_flush_single_request(struct dbc_request *req)
+{
+	union xhci_trb	*trb = req->trb;
+
+	trb->generic.field[0]	= 0;
+	trb->generic.field[1]	= 0;
+	trb->generic.field[2]	= 0;
+	trb->generic.field[3]	&= cpu_to_le32(TRB_CYCLE);
+	trb->generic.field[3]	|= cpu_to_le32(TRB_TYPE(TRB_TR_NOOP));
+
+	xhci_dbc_giveback(req, -ESHUTDOWN);
+}
+
+static void xhci_dbc_flush_endpoint_requests(struct dbc_ep *dep)
+{
+	struct dbc_request	*req, *tmp;
+
+	list_for_each_entry_safe(req, tmp, &dep->list_pending, list_pending)
+		xhci_dbc_flush_single_request(req);
+}
+
+static void xhci_dbc_flush_reqests(struct xhci_dbc *dbc)
+{
+	xhci_dbc_flush_endpoint_requests(&dbc->eps[BULK_OUT]);
+	xhci_dbc_flush_endpoint_requests(&dbc->eps[BULK_IN]);
+}
+
+struct dbc_request *
+dbc_alloc_request(struct dbc_ep *dep, gfp_t gfp_flags)
+{
+	struct dbc_request	*req;
+
+	req = kzalloc(sizeof(*req), gfp_flags);
+	if (!req)
+		return NULL;
+
+	req->dep = dep;
+	INIT_LIST_HEAD(&req->list_pending);
+	INIT_LIST_HEAD(&req->list_pool);
+	req->direction = dep->direction;
+
+	trace_xhci_dbc_alloc_request(req);
+
+	return req;
+}
+
+void
+dbc_free_request(struct dbc_ep *dep, struct dbc_request *req)
+{
+	trace_xhci_dbc_free_request(req);
+
+	kfree(req);
+}
+
+static void
+xhci_dbc_queue_trb(struct xhci_ring *ring, u32 field1,
+		   u32 field2, u32 field3, u32 field4)
+{
+	union xhci_trb		*trb, *next;
+
+	trb = ring->enqueue;
+	trb->generic.field[0]	= cpu_to_le32(field1);
+	trb->generic.field[1]	= cpu_to_le32(field2);
+	trb->generic.field[2]	= cpu_to_le32(field3);
+	trb->generic.field[3]	= cpu_to_le32(field4);
+
+	trace_xhci_dbc_gadget_ep_queue(ring, &trb->generic);
+
+	ring->num_trbs_free--;
+	next = ++(ring->enqueue);
+	if (TRB_TYPE_LINK_LE32(next->link.control)) {
+		next->link.control ^= cpu_to_le32(TRB_CYCLE);
+		ring->enqueue = ring->enq_seg->trbs;
+		ring->cycle_state ^= 1;
+	}
+}
+
+static int xhci_dbc_queue_bulk_tx(struct dbc_ep *dep,
+				  struct dbc_request *req)
+{
+	u64			addr;
+	union xhci_trb		*trb;
+	unsigned int		num_trbs;
+	struct xhci_dbc		*dbc = dep->dbc;
+	struct xhci_ring	*ring = dep->ring;
+	u32			length, control, cycle;
+
+	num_trbs = count_trbs(req->dma, req->length);
+	WARN_ON(num_trbs != 1);
+	if (ring->num_trbs_free < num_trbs)
+		return -EBUSY;
+
+	addr	= req->dma;
+	trb	= ring->enqueue;
+	cycle	= ring->cycle_state;
+	length	= TRB_LEN(req->length);
+	control	= TRB_TYPE(TRB_NORMAL) | TRB_IOC;
+
+	if (cycle)
+		control &= cpu_to_le32(~TRB_CYCLE);
+	else
+		control |= cpu_to_le32(TRB_CYCLE);
+
+	req->trb = ring->enqueue;
+	req->trb_dma = xhci_trb_virt_to_dma(ring->enq_seg, ring->enqueue);
+	xhci_dbc_queue_trb(ring,
+			   lower_32_bits(addr),
+			   upper_32_bits(addr),
+			   length, control);
+
+	/*
+	 * Add a barrier between writes of trb fields and flipping
+	 * the cycle bit:
+	 */
+	wmb();
+
+	if (cycle)
+		trb->generic.field[3] |= cpu_to_le32(TRB_CYCLE);
+	else
+		trb->generic.field[3] &= cpu_to_le32(~TRB_CYCLE);
+
+	writel(DBC_DOOR_BELL_TARGET(dep->direction), &dbc->regs->doorbell);
+
+	return 0;
+}
+
+static int
+dbc_ep_do_queue(struct dbc_ep *dep, struct dbc_request *req)
+{
+	int			ret;
+	struct device		*dev;
+	struct xhci_dbc		*dbc = dep->dbc;
+	struct xhci_hcd		*xhci = dbc->xhci;
+
+	dev = xhci_to_hcd(xhci)->self.sysdev;
+
+	if (!req->length || !req->buf)
+		return -EINVAL;
+
+	req->actual		= 0;
+	req->status		= -EINPROGRESS;
+
+	req->dma = dma_map_single(dev,
+				  req->buf,
+				  req->length,
+				  dbc_ep_dma_direction(dep));
+	if (dma_mapping_error(dev, req->dma)) {
+		xhci_err(xhci, "failed to map buffer\n");
+		return -EFAULT;
+	}
+
+	ret = xhci_dbc_queue_bulk_tx(dep, req);
+	if (ret) {
+		xhci_err(xhci, "failed to queue trbs\n");
+		dma_unmap_single(dev,
+				 req->dma,
+				 req->length,
+				 dbc_ep_dma_direction(dep));
+		return -EFAULT;
+	}
+
+	list_add_tail(&req->list_pending, &dep->list_pending);
+
+	return 0;
+}
+
+int dbc_ep_queue(struct dbc_ep *dep, struct dbc_request *req,
+		 gfp_t gfp_flags)
+{
+	struct xhci_dbc		*dbc = dep->dbc;
+	int			ret = -ESHUTDOWN;
+
+	spin_lock(&dbc->lock);
+	if (dbc->state == DS_CONFIGURED)
+		ret = dbc_ep_do_queue(dep, req);
+	spin_unlock(&dbc->lock);
+
+	mod_delayed_work(system_wq, &dbc->event_work, 0);
+
+	trace_xhci_dbc_queue_request(req);
+
+	return ret;
+}
+
+static inline void xhci_dbc_do_eps_init(struct xhci_hcd *xhci, bool direction)
+{
+	struct dbc_ep		*dep;
+	struct xhci_dbc		*dbc = xhci->dbc;
+
+	dep			= &dbc->eps[direction];
+	dep->dbc		= dbc;
+	dep->direction		= direction;
+	dep->ring		= direction ? dbc->ring_in : dbc->ring_out;
+
+	INIT_LIST_HEAD(&dep->list_pending);
+}
+
+static void xhci_dbc_eps_init(struct xhci_hcd *xhci)
+{
+	xhci_dbc_do_eps_init(xhci, BULK_OUT);
+	xhci_dbc_do_eps_init(xhci, BULK_IN);
+}
+
+static void xhci_dbc_eps_exit(struct xhci_hcd *xhci)
+{
+	struct xhci_dbc		*dbc = xhci->dbc;
+
+	memset(dbc->eps, 0, ARRAY_SIZE(dbc->eps));
+}
+
+static int xhci_dbc_mem_init(struct xhci_hcd *xhci, gfp_t flags)
+{
+	int			ret;
+	dma_addr_t		deq;
+	u32			string_length;
+	struct xhci_dbc		*dbc = xhci->dbc;
+
+	/* Allocate various rings for events and transfers: */
+	dbc->ring_evt = xhci_ring_alloc(xhci, 1, 1, TYPE_EVENT, 0, flags);
+	if (!dbc->ring_evt)
+		goto evt_fail;
+
+	dbc->ring_in = xhci_ring_alloc(xhci, 1, 1, TYPE_BULK, 0, flags);
+	if (!dbc->ring_in)
+		goto in_fail;
+
+	dbc->ring_out = xhci_ring_alloc(xhci, 1, 1, TYPE_BULK, 0, flags);
+	if (!dbc->ring_out)
+		goto out_fail;
+
+	/* Allocate and populate ERST: */
+	ret = xhci_alloc_erst(xhci, dbc->ring_evt, &dbc->erst, flags);
+	if (ret)
+		goto erst_fail;
+
+	/* Allocate context data structure: */
+	dbc->ctx = xhci_alloc_container_ctx(xhci, XHCI_CTX_TYPE_DEVICE, flags);
+	if (!dbc->ctx)
+		goto ctx_fail;
+
+	/* Allocate the string table: */
+	dbc->string_size = sizeof(struct dbc_str_descs);
+	dbc->string = dbc_dma_alloc_coherent(xhci,
+					     dbc->string_size,
+					     &dbc->string_dma,
+					     flags);
+	if (!dbc->string)
+		goto string_fail;
+
+	/* Setup ERST register: */
+	writel(dbc->erst.erst_size, &dbc->regs->ersts);
+	xhci_write_64(xhci, dbc->erst.erst_dma_addr, &dbc->regs->erstba);
+	deq = xhci_trb_virt_to_dma(dbc->ring_evt->deq_seg,
+				   dbc->ring_evt->dequeue);
+	xhci_write_64(xhci, deq, &dbc->regs->erdp);
+
+	/* Setup strings and contexts: */
+	string_length = xhci_dbc_populate_strings(dbc->string);
+	xhci_dbc_init_contexts(xhci, string_length);
+
+	mmiowb();
+
+	xhci_dbc_eps_init(xhci);
+	dbc->state = DS_INITIALIZED;
+
+	return 0;
+
+string_fail:
+	xhci_free_container_ctx(xhci, dbc->ctx);
+	dbc->ctx = NULL;
+ctx_fail:
+	xhci_free_erst(xhci, &dbc->erst);
+erst_fail:
+	xhci_ring_free(xhci, dbc->ring_out);
+	dbc->ring_out = NULL;
+out_fail:
+	xhci_ring_free(xhci, dbc->ring_in);
+	dbc->ring_in = NULL;
+in_fail:
+	xhci_ring_free(xhci, dbc->ring_evt);
+	dbc->ring_evt = NULL;
+evt_fail:
+	return -ENOMEM;
+}
+
+static void xhci_dbc_mem_cleanup(struct xhci_hcd *xhci)
+{
+	struct xhci_dbc		*dbc = xhci->dbc;
+
+	if (!dbc)
+		return;
+
+	xhci_dbc_eps_exit(xhci);
+
+	if (dbc->string) {
+		dbc_dma_free_coherent(xhci,
+				      dbc->string_size,
+				      dbc->string, dbc->string_dma);
+		dbc->string = NULL;
+	}
+
+	xhci_free_container_ctx(xhci, dbc->ctx);
+	dbc->ctx = NULL;
+
+	xhci_free_erst(xhci, &dbc->erst);
+	xhci_ring_free(xhci, dbc->ring_out);
+	xhci_ring_free(xhci, dbc->ring_in);
+	xhci_ring_free(xhci, dbc->ring_evt);
+	dbc->ring_in = NULL;
+	dbc->ring_out = NULL;
+	dbc->ring_evt = NULL;
+}
+
+static int xhci_do_dbc_start(struct xhci_hcd *xhci)
+{
+	int			ret;
+	u32			ctrl;
+	struct xhci_dbc		*dbc = xhci->dbc;
+
+	if (dbc->state != DS_DISABLED)
+		return -EINVAL;
+
+	writel(0, &dbc->regs->control);
+	ret = xhci_handshake(&dbc->regs->control,
+			     DBC_CTRL_DBC_ENABLE,
+			     0, 1000);
+	if (ret)
+		return ret;
+
+	ret = xhci_dbc_mem_init(xhci, GFP_ATOMIC);
+	if (ret)
+		return ret;
+
+	ctrl = readl(&dbc->regs->control);
+	writel(ctrl | DBC_CTRL_DBC_ENABLE | DBC_CTRL_PORT_ENABLE,
+	       &dbc->regs->control);
+	ret = xhci_handshake(&dbc->regs->control,
+			     DBC_CTRL_DBC_ENABLE,
+			     DBC_CTRL_DBC_ENABLE, 1000);
+	if (ret)
+		return ret;
+
+	dbc->state = DS_ENABLED;
+
+	return 0;
+}
+
+static void xhci_do_dbc_stop(struct xhci_hcd *xhci)
+{
+	struct xhci_dbc		*dbc = xhci->dbc;
+
+	if (dbc->state == DS_DISABLED)
+		return;
+
+	writel(0, &dbc->regs->control);
+	xhci_dbc_mem_cleanup(xhci);
+	dbc->state = DS_DISABLED;
+}
+
+static int xhci_dbc_start(struct xhci_hcd *xhci)
+{
+	int			ret;
+	struct xhci_dbc		*dbc = xhci->dbc;
+
+	WARN_ON(!dbc);
+
+	pm_runtime_get_sync(xhci_to_hcd(xhci)->self.controller);
+
+	spin_lock(&dbc->lock);
+	ret = xhci_do_dbc_start(xhci);
+	spin_unlock(&dbc->lock);
+
+	if (ret) {
+		pm_runtime_put(xhci_to_hcd(xhci)->self.controller);
+		return ret;
+	}
+
+	return mod_delayed_work(system_wq, &dbc->event_work, 1);
+}
+
+static void xhci_dbc_stop(struct xhci_hcd *xhci)
+{
+	struct xhci_dbc		*dbc = xhci->dbc;
+	struct dbc_port		*port = &dbc->port;
+
+	WARN_ON(!dbc);
+
+	cancel_delayed_work_sync(&dbc->event_work);
+
+	if (port->registered)
+		xhci_dbc_tty_unregister_device(xhci);
+
+	spin_lock(&dbc->lock);
+	xhci_do_dbc_stop(xhci);
+	spin_unlock(&dbc->lock);
+
+	pm_runtime_put_sync(xhci_to_hcd(xhci)->self.controller);
+}
+
+static void
+dbc_handle_port_status(struct xhci_hcd *xhci, union xhci_trb *event)
+{
+	u32			portsc;
+	struct xhci_dbc		*dbc = xhci->dbc;
+
+	portsc = readl(&dbc->regs->portsc);
+	if (portsc & DBC_PORTSC_CONN_CHANGE)
+		xhci_info(xhci, "DbC port connect change\n");
+
+	if (portsc & DBC_PORTSC_RESET_CHANGE)
+		xhci_info(xhci, "DbC port reset change\n");
+
+	if (portsc & DBC_PORTSC_LINK_CHANGE)
+		xhci_info(xhci, "DbC port link status change\n");
+
+	if (portsc & DBC_PORTSC_CONFIG_CHANGE)
+		xhci_info(xhci, "DbC config error change\n");
+
+	/* Port reset change bit will be cleared in other place: */
+	writel(portsc & ~DBC_PORTSC_RESET_CHANGE, &dbc->regs->portsc);
+}
+
+static void dbc_handle_xfer_event(struct xhci_hcd *xhci, union xhci_trb *event)
+{
+	struct dbc_ep		*dep;
+	struct xhci_ring	*ring;
+	int			ep_id;
+	int			status;
+	u32			comp_code;
+	size_t			remain_length;
+	struct dbc_request	*req = NULL, *r;
+
+	comp_code	= GET_COMP_CODE(le32_to_cpu(event->generic.field[2]));
+	remain_length	= EVENT_TRB_LEN(le32_to_cpu(event->generic.field[2]));
+	ep_id		= TRB_TO_EP_ID(le32_to_cpu(event->generic.field[3]));
+	dep		= (ep_id == EPID_OUT) ?
+				get_out_ep(xhci) : get_in_ep(xhci);
+	ring		= dep->ring;
+
+	switch (comp_code) {
+	case COMP_SUCCESS:
+		remain_length = 0;
+	/* FALLTHROUGH */
+	case COMP_SHORT_PACKET:
+		status = 0;
+		break;
+	case COMP_TRB_ERROR:
+	case COMP_BABBLE_DETECTED_ERROR:
+	case COMP_USB_TRANSACTION_ERROR:
+	case COMP_STALL_ERROR:
+		xhci_warn(xhci, "tx error %d detected\n", comp_code);
+		status = -comp_code;
+		break;
+	default:
+		xhci_err(xhci, "unknown tx error %d\n", comp_code);
+		status = -comp_code;
+		break;
+	}
+
+	/* Match the pending request: */
+	list_for_each_entry(r, &dep->list_pending, list_pending) {
+		if (r->trb_dma == event->trans_event.buffer) {
+			req = r;
+			break;
+		}
+	}
+
+	if (!req) {
+		xhci_warn(xhci, "no matched request\n");
+		return;
+	}
+
+	trace_xhci_dbc_handle_transfer(ring, &req->trb->generic);
+
+	ring->num_trbs_free++;
+	req->actual = req->length - remain_length;
+	xhci_dbc_giveback(req, status);
+}
+
+static enum evtreturn xhci_dbc_do_handle_events(struct xhci_dbc *dbc)
+{
+	dma_addr_t		deq;
+	struct dbc_ep		*dep;
+	union xhci_trb		*evt;
+	u32			ctrl, portsc;
+	struct xhci_hcd		*xhci = dbc->xhci;
+	bool			update_erdp = false;
+
+	/* DbC state machine: */
+	switch (dbc->state) {
+	case DS_DISABLED:
+	case DS_INITIALIZED:
+
+		return EVT_ERR;
+	case DS_ENABLED:
+		portsc = readl(&dbc->regs->portsc);
+		if (portsc & DBC_PORTSC_CONN_STATUS) {
+			dbc->state = DS_CONNECTED;
+			xhci_info(xhci, "DbC connected\n");
+		}
+
+		return EVT_DONE;
+	case DS_CONNECTED:
+		ctrl = readl(&dbc->regs->control);
+		if (ctrl & DBC_CTRL_DBC_RUN) {
+			dbc->state = DS_CONFIGURED;
+			xhci_info(xhci, "DbC configured\n");
+			portsc = readl(&dbc->regs->portsc);
+			writel(portsc, &dbc->regs->portsc);
+			return EVT_GSER;
+		}
+
+		return EVT_DONE;
+	case DS_CONFIGURED:
+		/* Handle cable unplug event: */
+		portsc = readl(&dbc->regs->portsc);
+		if (!(portsc & DBC_PORTSC_PORT_ENABLED) &&
+		    !(portsc & DBC_PORTSC_CONN_STATUS)) {
+			xhci_info(xhci, "DbC cable unplugged\n");
+			dbc->state = DS_ENABLED;
+			xhci_dbc_flush_reqests(dbc);
+
+			return EVT_DISC;
+		}
+
+		/* Handle debug port reset event: */
+		if (portsc & DBC_PORTSC_RESET_CHANGE) {
+			xhci_info(xhci, "DbC port reset\n");
+			writel(portsc, &dbc->regs->portsc);
+			dbc->state = DS_ENABLED;
+			xhci_dbc_flush_reqests(dbc);
+
+			return EVT_DISC;
+		}
+
+		/* Handle endpoint stall event: */
+		ctrl = readl(&dbc->regs->control);
+		if ((ctrl & DBC_CTRL_HALT_IN_TR) ||
+		    (ctrl & DBC_CTRL_HALT_OUT_TR)) {
+			xhci_info(xhci, "DbC Endpoint stall\n");
+			dbc->state = DS_STALLED;
+
+			if (ctrl & DBC_CTRL_HALT_IN_TR) {
+				dep = get_in_ep(xhci);
+				xhci_dbc_flush_endpoint_requests(dep);
+			}
+
+			if (ctrl & DBC_CTRL_HALT_OUT_TR) {
+				dep = get_out_ep(xhci);
+				xhci_dbc_flush_endpoint_requests(dep);
+			}
+
+			return EVT_DONE;
+		}
+
+		/* Clear DbC run change bit: */
+		if (ctrl & DBC_CTRL_DBC_RUN_CHANGE) {
+			writel(ctrl, &dbc->regs->control);
+			ctrl = readl(&dbc->regs->control);
+		}
+
+		break;
+	case DS_STALLED:
+		ctrl = readl(&dbc->regs->control);
+		if (!(ctrl & DBC_CTRL_HALT_IN_TR) &&
+		    !(ctrl & DBC_CTRL_HALT_OUT_TR) &&
+		    (ctrl & DBC_CTRL_DBC_RUN)) {
+			dbc->state = DS_CONFIGURED;
+			break;
+		}
+
+		return EVT_DONE;
+	default:
+		xhci_err(xhci, "Unknown DbC state %d\n", dbc->state);
+		break;
+	}
+
+	/* Handle the events in the event ring: */
+	evt = dbc->ring_evt->dequeue;
+	while ((le32_to_cpu(evt->event_cmd.flags) & TRB_CYCLE) ==
+			dbc->ring_evt->cycle_state) {
+		/*
+		 * Add a barrier between reading the cycle flag and any
+		 * reads of the event's flags/data below:
+		 */
+		rmb();
+
+		trace_xhci_dbc_handle_event(dbc->ring_evt, &evt->generic);
+
+		switch (le32_to_cpu(evt->event_cmd.flags) & TRB_TYPE_BITMASK) {
+		case TRB_TYPE(TRB_PORT_STATUS):
+			dbc_handle_port_status(xhci, evt);
+			break;
+		case TRB_TYPE(TRB_TRANSFER):
+			dbc_handle_xfer_event(xhci, evt);
+			break;
+		default:
+			break;
+		}
+
+		inc_deq(xhci, dbc->ring_evt);
+		evt = dbc->ring_evt->dequeue;
+		update_erdp = true;
+	}
+
+	/* Update event ring dequeue pointer: */
+	if (update_erdp) {
+		deq = xhci_trb_virt_to_dma(dbc->ring_evt->deq_seg,
+					   dbc->ring_evt->dequeue);
+		xhci_write_64(xhci, deq, &dbc->regs->erdp);
+	}
+
+	return EVT_DONE;
+}
+
+static void xhci_dbc_handle_events(struct work_struct *work)
+{
+	int			ret;
+	enum evtreturn		evtr;
+	struct xhci_dbc		*dbc;
+	struct xhci_hcd		*xhci;
+
+	dbc = container_of(to_delayed_work(work), struct xhci_dbc, event_work);
+	xhci = dbc->xhci;
+
+	spin_lock(&dbc->lock);
+	evtr = xhci_dbc_do_handle_events(dbc);
+	spin_unlock(&dbc->lock);
+
+	switch (evtr) {
+	case EVT_GSER:
+		ret = xhci_dbc_tty_register_device(xhci);
+		if (ret) {
+			xhci_err(xhci, "failed to alloc tty device\n");
+			break;
+		}
+
+		xhci_info(xhci, "DbC now attached to /dev/ttyDBC0\n");
+		break;
+	case EVT_DISC:
+		xhci_dbc_tty_unregister_device(xhci);
+		break;
+	case EVT_DONE:
+		break;
+	default:
+		xhci_info(xhci, "stop handling dbc events\n");
+		return;
+	}
+
+	mod_delayed_work(system_wq, &dbc->event_work, 1);
+}
+
+static void xhci_do_dbc_exit(struct xhci_hcd *xhci)
+{
+	unsigned long		flags;
+
+	spin_lock_irqsave(&xhci->lock, flags);
+	kfree(xhci->dbc);
+	xhci->dbc = NULL;
+	spin_unlock_irqrestore(&xhci->lock, flags);
+}
+
+static int xhci_do_dbc_init(struct xhci_hcd *xhci)
+{
+	u32			reg;
+	struct xhci_dbc		*dbc;
+	unsigned long		flags;
+	void __iomem		*base;
+	int			dbc_cap_offs;
+
+	base = &xhci->cap_regs->hc_capbase;
+	dbc_cap_offs = xhci_find_next_ext_cap(base, 0, XHCI_EXT_CAPS_DEBUG);
+	if (!dbc_cap_offs)
+		return -ENODEV;
+
+	dbc = kzalloc(sizeof(*dbc), GFP_KERNEL);
+	if (!dbc)
+		return -ENOMEM;
+
+	dbc->regs = base + dbc_cap_offs;
+
+	/* We will avoid using DbC in xhci driver if it's in use. */
+	reg = readl(&dbc->regs->control);
+	if (reg & DBC_CTRL_DBC_ENABLE) {
+		kfree(dbc);
+		return -EBUSY;
+	}
+
+	spin_lock_irqsave(&xhci->lock, flags);
+	if (xhci->dbc) {
+		spin_unlock_irqrestore(&xhci->lock, flags);
+		kfree(dbc);
+		return -EBUSY;
+	}
+	xhci->dbc = dbc;
+	spin_unlock_irqrestore(&xhci->lock, flags);
+
+	dbc->xhci = xhci;
+	INIT_DELAYED_WORK(&dbc->event_work, xhci_dbc_handle_events);
+	spin_lock_init(&dbc->lock);
+
+	return 0;
+}
+
+static ssize_t dbc_show(struct device *dev,
+			struct device_attribute *attr,
+			char *buf)
+{
+	const char		*p;
+	struct xhci_dbc		*dbc;
+	struct xhci_hcd		*xhci;
+
+	xhci = hcd_to_xhci(dev_get_drvdata(dev));
+	dbc = xhci->dbc;
+
+	switch (dbc->state) {
+	case DS_DISABLED:
+		p = "disabled";
+		break;
+	case DS_INITIALIZED:
+		p = "initialized";
+		break;
+	case DS_ENABLED:
+		p = "enabled";
+		break;
+	case DS_CONNECTED:
+		p = "connected";
+		break;
+	case DS_CONFIGURED:
+		p = "configured";
+		break;
+	case DS_STALLED:
+		p = "stalled";
+		break;
+	default:
+		p = "unknown";
+	}
+
+	return sprintf(buf, "%s\n", p);
+}
+
+static ssize_t dbc_store(struct device *dev,
+			 struct device_attribute *attr,
+			 const char *buf, size_t count)
+{
+	struct xhci_dbc		*dbc;
+	struct xhci_hcd		*xhci;
+
+	xhci = hcd_to_xhci(dev_get_drvdata(dev));
+	dbc = xhci->dbc;
+
+	if (!strncmp(buf, "enable", 6))
+		xhci_dbc_start(xhci);
+	else if (!strncmp(buf, "disable", 7))
+		xhci_dbc_stop(xhci);
+	else
+		return -EINVAL;
+
+	return count;
+}
+
+static DEVICE_ATTR(dbc, 0644, dbc_show, dbc_store);
+
+int xhci_dbc_init(struct xhci_hcd *xhci)
+{
+	int			ret;
+	struct device		*dev = xhci_to_hcd(xhci)->self.controller;
+
+	ret = xhci_do_dbc_init(xhci);
+	if (ret)
+		goto init_err3;
+
+	ret = xhci_dbc_tty_register_driver(xhci);
+	if (ret)
+		goto init_err2;
+
+	ret = device_create_file(dev, &dev_attr_dbc);
+	if (ret)
+		goto init_err1;
+
+	return 0;
+
+init_err1:
+	xhci_dbc_tty_unregister_driver();
+init_err2:
+	xhci_do_dbc_exit(xhci);
+init_err3:
+	return ret;
+}
+
+void xhci_dbc_exit(struct xhci_hcd *xhci)
+{
+	struct device		*dev = xhci_to_hcd(xhci)->self.controller;
+
+	if (!xhci->dbc)
+		return;
+
+	device_remove_file(dev, &dev_attr_dbc);
+	xhci_dbc_tty_unregister_driver();
+	xhci_dbc_stop(xhci);
+	xhci_do_dbc_exit(xhci);
+}
+
+#ifdef CONFIG_PM
+int xhci_dbc_suspend(struct xhci_hcd *xhci)
+{
+	struct xhci_dbc		*dbc = xhci->dbc;
+
+	if (!dbc)
+		return 0;
+
+	if (dbc->state == DS_CONFIGURED)
+		dbc->resume_required = 1;
+
+	xhci_dbc_stop(xhci);
+
+	return 0;
+}
+
+int xhci_dbc_resume(struct xhci_hcd *xhci)
+{
+	int			ret = 0;
+	struct xhci_dbc		*dbc = xhci->dbc;
+
+	if (!dbc)
+		return 0;
+
+	if (dbc->resume_required) {
+		dbc->resume_required = 0;
+		xhci_dbc_start(xhci);
+	}
+
+	return ret;
+}
+#endif /* CONFIG_PM */