[PATCH 2/2] drm/self_refresh: Disable self-refresh on input events

[Brian Norris <briannorris@chromium.org>]

To improve panel self-refresh exit latency, we speculatively start
exiting when we
receive input events. Occasionally, this may lead to false positives,
but most of the time we get a head start on coming out of PSR. Depending
on how userspace takes to produce a new frame in response to the event,
this can completely hide the exit latency.

In local tests on Chrome OS (Rockchip RK3399 eDP), we've found that the
input notifier gives us about a 50ms head start over the
fb-update-initiated exit.

Leverage a new drm_input_helper library to get easy access to
likely-relevant input event callbacks.

Inspired-by: Kristian H. Kristensen <hoegsberg@google.com>
Signed-off-by: Brian Norris <briannorris@chromium.org>
---
This was in part picked up from:

  https://lore.kernel.org/all/20180405095000.9756-25-enric.balletbo@collabora.com/
  [PATCH v6 24/30] drm/rockchip: Disable PSR on input events

with significant rewrites/reworks:

 - moved to common drm_input_helper and drm_self_refresh_helper
   implementation
 - track state only through crtc->state->self_refresh_active

Note that I'm relatively unfamiliar with DRM locking expectations, but I
believe access to drm_crtc->state (which helps us track redundant
transitions) is OK under the locking provided by
drm_atomic_get_crtc_state().

 drivers/gpu/drm/drm_self_refresh_helper.c | 54 ++++++++++++++++++++---
 1 file changed, 48 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/drm_self_refresh_helper.c b/drivers/gpu/drm/drm_self_refresh_helper.c
index dd33fec5aabd..dcab061cc90a 100644
--- a/drivers/gpu/drm/drm_self_refresh_helper.c
+++ b/drivers/gpu/drm/drm_self_refresh_helper.c
@@ -15,6 +15,7 @@
 #include <drm/drm_connector.h>
 #include <drm/drm_crtc.h>
 #include <drm/drm_device.h>
+#include <drm/drm_input_helper.h>
 #include <drm/drm_mode_config.h>
 #include <drm/drm_modeset_lock.h>
 #include <drm/drm_print.h>
@@ -58,17 +59,17 @@ DECLARE_EWMA(psr_time, 4, 4)
 struct drm_self_refresh_data {
 	struct drm_crtc *crtc;
 	struct delayed_work entry_work;
+	struct work_struct exit_work;
+	struct drm_input_handler input_handler;
 
 	struct mutex avg_mutex;
 	struct ewma_psr_time entry_avg_ms;
 	struct ewma_psr_time exit_avg_ms;
 };
 
-static void drm_self_refresh_helper_entry_work(struct work_struct *work)
+static void drm_self_refresh_transition(struct drm_self_refresh_data *sr_data,
+					bool enable)
 {
-	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;
@@ -95,6 +96,9 @@ static void drm_self_refresh_helper_entry_work(struct work_struct *work)
 		goto out;
 	}
 
+	if (crtc->state->self_refresh_active == enable)
+		goto out;
+
 	if (!crtc_state->enable)
 		goto out;
 
@@ -107,8 +111,8 @@ static void drm_self_refresh_helper_entry_work(struct work_struct *work)
 			goto out;
 	}
 
-	crtc_state->active = false;
-	crtc_state->self_refresh_active = true;
+	crtc_state->active = !enable;
+	crtc_state->self_refresh_active = enable;
 
 	ret = drm_atomic_commit(state);
 	if (ret)
@@ -129,6 +133,15 @@ static void drm_self_refresh_helper_entry_work(struct work_struct *work)
 	drm_modeset_acquire_fini(&ctx);
 }
 
+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);
+
+	drm_self_refresh_transition(sr_data, true);
+}
+
 /**
  * drm_self_refresh_helper_update_avg_times - Updates a crtc's SR time averages
  * @state: the state which has just been applied to hardware
@@ -223,6 +236,20 @@ void drm_self_refresh_helper_alter_state(struct drm_atomic_state *state)
 }
 EXPORT_SYMBOL(drm_self_refresh_helper_alter_state);
 
+static void drm_self_refresh_helper_exit_work(struct work_struct *work)
+{
+	struct drm_self_refresh_data *sr_data = container_of(
+			work, struct drm_self_refresh_data, exit_work);
+
+	drm_self_refresh_transition(sr_data, false);
+}
+
+static void drm_self_refresh_input_event(void *data)
+{
+	struct drm_self_refresh_data *sr_data = data;
+
+	schedule_work(&sr_data->exit_work);
+}
 /**
  * drm_self_refresh_helper_init - Initializes self refresh helpers for a crtc
  * @crtc: the crtc which supports self refresh supported displays
@@ -232,6 +259,7 @@ EXPORT_SYMBOL(drm_self_refresh_helper_alter_state);
 int drm_self_refresh_helper_init(struct drm_crtc *crtc)
 {
 	struct drm_self_refresh_data *sr_data = crtc->self_refresh_data;
+	int ret;
 
 	/* Helper is already initialized */
 	if (WARN_ON(sr_data))
@@ -243,6 +271,7 @@ int drm_self_refresh_helper_init(struct drm_crtc *crtc)
 
 	INIT_DELAYED_WORK(&sr_data->entry_work,
 			  drm_self_refresh_helper_entry_work);
+	INIT_WORK(&sr_data->exit_work, drm_self_refresh_helper_exit_work);
 	sr_data->crtc = crtc;
 	mutex_init(&sr_data->avg_mutex);
 	ewma_psr_time_init(&sr_data->entry_avg_ms);
@@ -256,8 +285,19 @@ int drm_self_refresh_helper_init(struct drm_crtc *crtc)
 	ewma_psr_time_add(&sr_data->entry_avg_ms, SELF_REFRESH_AVG_SEED_MS);
 	ewma_psr_time_add(&sr_data->exit_avg_ms, SELF_REFRESH_AVG_SEED_MS);
 
+	sr_data->input_handler.callback = drm_self_refresh_input_event;
+	sr_data->input_handler.priv = sr_data;
+	ret = drm_input_handle_register(crtc->dev, &sr_data->input_handler);
+	if (ret)
+		goto err;
+
 	crtc->self_refresh_data = sr_data;
+
 	return 0;
+
+err:
+	kfree(sr_data);
+	return ret;
 }
 EXPORT_SYMBOL(drm_self_refresh_helper_init);
 
@@ -275,7 +315,9 @@ void drm_self_refresh_helper_cleanup(struct drm_crtc *crtc)
 
 	crtc->self_refresh_data = NULL;
 
+	drm_input_handle_unregister(&sr_data->input_handler);
 	cancel_delayed_work_sync(&sr_data->entry_work);
+	cancel_work_sync(&sr_data->exit_work);
 	kfree(sr_data);
 }
 EXPORT_SYMBOL(drm_self_refresh_helper_cleanup);
-- 
2.34.0.rc0.344.g81b53c2807-goog