drm: Add helpers to kick off self refresh mode in drivers

This patch adds a new drm helper library to help drivers implement
self refresh. Drivers choosing to use it will register crtcs and
will receive callbacks when it's time to enter or exit self refresh
mode.

In its current form, it has a timer which will trigger after a
driver-specified amount of inactivity. When the timer triggers, the
helpers will submit a new atomic commit to shut the refreshing pipe
off. On the next atomic commit, the drm core will revert the self
refresh state and bring everything back up to be actively driven.

From the driver's perspective, this works like a regular disable/enable
cycle. The driver need only check the 'self_refresh_active' state in
crtc_state. It should initiate self refresh mode on the panel and enter
an off or low-power state.

Changes in v2:
- s/psr/self_refresh/ (Daniel)
- integrated the psr exit into the commit that wakes it up (Jose/Daniel)
- made the psr state per-crtc (Jose/Daniel)
Changes in v3:
- Remove the self_refresh_(active|changed) from connector state (Daniel)
- Simplify loop in drm_self_refresh_helper_alter_state (Daniel)
- Improve self_refresh_aware comment (Daniel)
- s/self_refresh_state/self_refresh_data/ (Daniel)
Changes in v4:
- Move docbook location below panel (Daniel)
- Improve docbook with references and more detailed explanation (Daniel)
- Instead of register/unregister, use init/cleanup (Daniel)
Changes in v5:
- Resolved conflict in drm_atomic_helper.c #include block
- Resolved conflict in rst with HDCP helper docs
Changes in v6:
- Fix include ordering, clean up forward declarations (Sam)

Link to v1: https://patchwork.freedesktop.org/patch/msgid/20190228210939.83386-2-sean@poorly.run
Link to v2: https://patchwork.freedesktop.org/patch/msgid/20190326204509.96515-1-sean@poorly.run
Link to v3: https://patchwork.freedesktop.org/patch/msgid/20190502194956.218441-6-sean@poorly.run
Link to v4: https://patchwork.freedesktop.org/patch/msgid/20190508160920.144739-6-sean@poorly.run
Link to v5: https://patchwork.freedesktop.org/patch/msgid/20190611160844.257498-6-sean@poorly.run

Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Jose Souza <jose.souza@intel.com>
Cc: Zain Wang <wzz@rock-chips.com>
Cc: Tomasz Figa <tfiga@chromium.org>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190612145026.191846-1-sean@poorly.run

1 files changed, 216 insertions, 0 deletions

diff --git a/drivers/gpu/drm/drm_self_refresh_helper.c b/drivers/gpu/drm/drm_self_refresh_helper.c
new file mode 100644
index 000000000000..2b3daaf77841
--- /dev/null
+++ b/drivers/gpu/drm/drm_self_refresh_helper.c
@@ -0,0 +1,216 @@
+// SPDX-License-Identifier: MIT
+/*
+ * Copyright (C) 2019 Google, Inc.
+ *
+ * Authors:
+ * Sean Paul <seanpaul@chromium.org>
+ */
+#include <linux/bitops.h>
+#include <linux/slab.h>
+#include <linux/workqueue.h>
+
+#include <drm/drm_atomic.h>
+#include <drm/drm_atomic_helper.h>
+#include <drm/drm_connector.h>
+#include <drm/drm_crtc.h>
+#include <drm/drm_device.h>
+#include <drm/drm_mode_config.h>
+#include <drm/drm_modeset_lock.h>
+#include <drm/drm_print.h>
+#include <drm/drm_self_refresh_helper.h>
+
+/**
+ * DOC: overview
+ *
+ * This helper library provides an easy way for drivers to leverage the atomic
+ * framework to implement panel self refresh (SR) support. Drivers are
+ * responsible for initializing and cleaning up the SR helpers on load/unload
+ * (see &drm_self_refresh_helper_init/&drm_self_refresh_helper_cleanup).
+ * The connector is responsible for setting
+ * &drm_connector_state.self_refresh_aware to true at runtime if it is SR-aware
+ * (meaning it knows how to initiate self refresh on the panel).
+ *
+ * Once a crtc has enabled SR using &drm_self_refresh_helper_init, the
+ * helpers will monitor activity and call back into the driver to enable/disable
+ * SR as appropriate. The best way to think about this is that it's a DPMS
+ * on/off request with &drm_crtc_state.self_refresh_active set in crtc state
+ * that tells you to disable/enable SR on the panel instead of power-cycling it.
+ *
+ * During SR, drivers may choose to fully disable their crtc/encoder/bridge
+ * hardware (in which case no driver changes are necessary), or they can inspect
+ * &drm_crtc_state.self_refresh_active if they want to enter low power mode
+ * without full disable (in case full disable/enable is too slow).
+ *
+ * SR will be deactivated if there are any atomic updates affecting the
+ * pipe that is in SR mode. If a crtc is driving multiple connectors, all
+ * connectors must be SR aware and all will enter/exit SR mode at the same time.
+ *
+ * If the crtc and connector are SR aware, but the panel connected does not
+ * support it (or is otherwise unable to enter SR), the driver should fail
+ * atomic_check when &drm_crtc_state.self_refresh_active is true.
+ */
+
+struct drm_self_refresh_data {
+	struct drm_crtc *crtc;
+	struct delayed_work entry_work;
+	struct drm_atomic_state *save_state;
+	unsigned int entry_delay_ms;
+};
+
+static void drm_self_refresh_helper_entry_work(struct work_struct *work)
+{
+	struct drm_self_refresh_data *sr_data = container_of(
+				to_delayed_work(work),
+				struct drm_self_refresh_data, entry_work);
+	struct drm_crtc *crtc = sr_data->crtc;
+	struct drm_device *dev = crtc->dev;
+	struct drm_modeset_acquire_ctx ctx;
+	struct drm_atomic_state *state;
+	struct drm_connector *conn;
+	struct drm_connector_state *conn_state;
+	struct drm_crtc_state *crtc_state;
+	int i, ret;
+
+	drm_modeset_acquire_init(&ctx, 0);
+
+	state = drm_atomic_state_alloc(dev);
+	if (!state) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+retry:
+	state->acquire_ctx = &ctx;
+
+	crtc_state = drm_atomic_get_crtc_state(state, crtc);
+	if (IS_ERR(crtc_state)) {
+		ret = PTR_ERR(crtc_state);
+		goto out;
+	}
+
+	if (!crtc_state->enable)
+		goto out;
+
+	ret = drm_atomic_add_affected_connectors(state, crtc);
+	if (ret)
+		goto out;
+
+	for_each_new_connector_in_state(state, conn, conn_state, i) {
+		if (!conn_state->self_refresh_aware)
+			goto out;
+	}
+
+	crtc_state->active = false;
+	crtc_state->self_refresh_active = true;
+
+	ret = drm_atomic_commit(state);
+	if (ret)
+		goto out;
+
+out:
+	if (ret == -EDEADLK) {
+		drm_atomic_state_clear(state);
+		ret = drm_modeset_backoff(&ctx);
+		if (!ret)
+			goto retry;
+	}
+
+	drm_atomic_state_put(state);
+	drm_modeset_drop_locks(&ctx);
+	drm_modeset_acquire_fini(&ctx);
+}
+
+/**
+ * drm_self_refresh_helper_alter_state - Alters the atomic state for SR exit
+ * @state: the state currently being checked
+ *
+ * Called at the end of atomic check. This function checks the state for flags
+ * incompatible with self refresh exit and changes them. This is a bit
+ * disingenuous since userspace is expecting one thing and we're giving it
+ * another. However in order to keep self refresh entirely hidden from
+ * userspace, this is required.
+ *
+ * At the end, we queue up the self refresh entry work so we can enter PSR after
+ * the desired delay.
+ */
+void drm_self_refresh_helper_alter_state(struct drm_atomic_state *state)
+{
+	struct drm_crtc *crtc;
+	struct drm_crtc_state *crtc_state;
+	int i;
+
+	if (state->async_update || !state->allow_modeset) {
+		for_each_old_crtc_in_state(state, crtc, crtc_state, i) {
+			if (crtc_state->self_refresh_active) {
+				state->async_update = false;
+				state->allow_modeset = true;
+				break;
+			}
+		}
+	}
+
+	for_each_new_crtc_in_state(state, crtc, crtc_state, i) {
+		struct drm_self_refresh_data *sr_data;
+
+		/* Don't trigger the entry timer when we're already in SR */
+		if (crtc_state->self_refresh_active)
+			continue;
+
+		sr_data = crtc->self_refresh_data;
+		if (!sr_data)
+			continue;
+
+		mod_delayed_work(system_wq, &sr_data->entry_work,
+				 msecs_to_jiffies(sr_data->entry_delay_ms));
+	}
+}
+EXPORT_SYMBOL(drm_self_refresh_helper_alter_state);
+
+/**
+ * drm_self_refresh_helper_init - Initializes self refresh helpers for a crtc
+ * @crtc: the crtc which supports self refresh supported displays
+ * @entry_delay_ms: amount of inactivity to wait before entering self refresh
+ *
+ * Returns zero if successful or -errno on failure
+ */
+int drm_self_refresh_helper_init(struct drm_crtc *crtc,
+				 unsigned int entry_delay_ms)
+{
+	struct drm_self_refresh_data *sr_data = crtc->self_refresh_data;
+
+	/* Helper is already initialized */
+	if (WARN_ON(sr_data))
+		return -EINVAL;
+
+	sr_data = kzalloc(sizeof(*sr_data), GFP_KERNEL);
+	if (!sr_data)
+		return -ENOMEM;
+
+	INIT_DELAYED_WORK(&sr_data->entry_work,
+			  drm_self_refresh_helper_entry_work);
+	sr_data->entry_delay_ms = entry_delay_ms;
+	sr_data->crtc = crtc;
+
+	crtc->self_refresh_data = sr_data;
+	return 0;
+}
+EXPORT_SYMBOL(drm_self_refresh_helper_init);
+
+/**
+ * drm_self_refresh_helper_cleanup - Cleans up self refresh helpers for a crtc
+ * @crtc: the crtc to cleanup
+ */
+void drm_self_refresh_helper_cleanup(struct drm_crtc *crtc)
+{
+	struct drm_self_refresh_data *sr_data = crtc->self_refresh_data;
+
+	/* Helper is already uninitialized */
+	if (sr_data)
+		return;
+
+	crtc->self_refresh_data = NULL;
+
+	cancel_delayed_work_sync(&sr_data->entry_work);
+	kfree(sr_data);
+}
+EXPORT_SYMBOL(drm_self_refresh_helper_cleanup);