drm/i915: Fixing mutex deadlock window at eDP DRRS

In invalidate and flush functions of eDP DRRS, if deferred downclock
work starts execution at a time window between acquiring the drrs
mutex and cancellation of the deferred work
(intel_edp_drrs_downclock_work), then deferred work will find
drrs mutex locked and wait for the same.

Meanwhile the function that acquired mutex drrs invalidate/flush will
wait for the completion of the deferred work before releasing the mutex.
Thats a deadlock.

To avoid such deadlock scenario, this change cancels the deferred work
before acquiring the mutex at invalidate and flush functions.
Signed-off-by: NRamalingam C <ramalingam.c@intel.com>
Reviewed-by: NRodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_dp.c

@@ -4966,12 +4966,13 @@ void intel_edp_drrs_invalidate(struct drm_device *dev,
 	if (!dev_priv->drrs.dp)
 		return;
 
+	cancel_delayed_work_sync(&dev_priv->drrs.work);
+
 	mutex_lock(&dev_priv->drrs.mutex);
 	crtc = dp_to_dig_port(dev_priv->drrs.dp)->base.base.crtc;
 	pipe = to_intel_crtc(crtc)->pipe;
 
 	if (dev_priv->drrs.refresh_rate_type == DRRS_LOW_RR) {
-		cancel_delayed_work_sync(&dev_priv->drrs.work);
 		intel_dp_set_drrs_state(dev_priv->dev,
 				dev_priv->drrs.dp->attached_connector->panel.
 				fixed_mode->vrefresh);
@@ -5004,13 +5005,13 @@ void intel_edp_drrs_flush(struct drm_device *dev,
 	if (!dev_priv->drrs.dp)
 		return;
 
+	cancel_delayed_work_sync(&dev_priv->drrs.work);
+
 	mutex_lock(&dev_priv->drrs.mutex);
 	crtc = dp_to_dig_port(dev_priv->drrs.dp)->base.base.crtc;
 	pipe = to_intel_crtc(crtc)->pipe;
 	dev_priv->drrs.busy_frontbuffer_bits &= ~frontbuffer_bits;
 
-	cancel_delayed_work_sync(&dev_priv->drrs.work);
-
 	if (dev_priv->drrs.refresh_rate_type != DRRS_LOW_RR &&
 			!dev_priv->drrs.busy_frontbuffer_bits)
 		schedule_delayed_work(&dev_priv->drrs.work,