drm: rcar-du: Fix race condition when disabling planes at CRTC stop

When stopping the CRTC the driver must disable all planes and wait for
the change to take effect at the next vblank. Merely calling
drm_crtc_wait_one_vblank() is not enough, as the function doesn't
include any mechanism to handle the race with vblank interrupts.

Replace the drm_crtc_wait_one_vblank() call with a manual mechanism that
handles the vblank interrupt race.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/drivers/gpu/drm/rcar-du/rcar_du_crtc.h b/drivers/gpu/drm/rcar-du/rcar_du_crtc.h
index 3cc376826592..065b91f5b1d9 100644
--- a/drivers/gpu/drm/rcar-du/rcar_du_crtc.h
+++ b/drivers/gpu/drm/rcar-du/rcar_du_crtc.h
@@ -15,6 +15,7 @@
 #define __RCAR_DU_CRTC_H__
 
 #include <linux/mutex.h>
+#include <linux/spinlock.h>
 #include <linux/wait.h>
 
 #include <drm/drmP.h>
@@ -33,6 +34,9 @@ struct rcar_du_vsp;
  * @initialized: whether the CRTC has been initialized and clocks enabled
  * @event: event to post when the pending page flip completes
  * @flip_wait: wait queue used to signal page flip completion
+ * @vblank_lock: protects vblank_wait and vblank_count
+ * @vblank_wait: wait queue used to signal vertical blanking
+ * @vblank_count: number of vertical blanking interrupts to wait for
  * @outputs: bitmask of the outputs (enum rcar_du_output) driven by this CRTC
  * @group: CRTC group this CRTC belongs to
  * @vsp: VSP feeding video to this CRTC
@@ -50,6 +54,10 @@ struct rcar_du_crtc {
 	struct drm_pending_vblank_event *event;
 	wait_queue_head_t flip_wait;
 
+	spinlock_t vblank_lock;
+	wait_queue_head_t vblank_wait;
+	unsigned int vblank_count;
+
 	unsigned int outputs;
 
 	struct rcar_du_group *group;