drm: rcar-du: Repair vblank for DRM page flips using the VSP

The driver recently switched from handling page flip completion in the
DU vertical blanking handler to the VSP frame end handler to fix a race
condition. This unfortunately resulted in incorrect timestamps in the
vertical blanking events sent to userspace as vertical blanking is now
handled after sending the event.

To fix this we must reverse the order of the two operations. The easiest
way is to handle vertical blanking in the VSP frame end handler before
sending the event. The VSP frame end interrupt occurs approximately 50µs
earlier than the DU frame end interrupt, but this should not cause any
undue harm.

As we need to handle vertical blanking even when page flip completion is
delayed, the VSP driver now needs to call the frame end completion
callback unconditionally, with a new argument to report whether page
flip has completed.

With this new scheme the DU vertical blanking interrupt isn't needed
anymore, so we can stop enabling it.

Fixes: d503a43ac06a ("drm: rcar-du: Register a completion callback with VSP1")
Signed-off-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

1 files changed, 2 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 065b91f5b1d9..fdc2bf99bda1 100644
--- a/drivers/gpu/drm/rcar-du/rcar_du_crtc.h
+++ b/drivers/gpu/drm/rcar-du/rcar_du_crtc.h
@@ -32,6 +32,7 @@ struct rcar_du_vsp;
  * @mmio_offset: offset of the CRTC registers in the DU MMIO block
  * @index: CRTC software and hardware index
  * @initialized: whether the CRTC has been initialized and clocks enabled
+ * @vblank_enable: whether vblank events are enabled on this CRTC
  * @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
@@ -51,6 +52,7 @@ struct rcar_du_crtc {
 	unsigned int index;
 	bool initialized;
 
+	bool vblank_enable;
 	struct drm_pending_vblank_event *event;
 	wait_queue_head_t flip_wait;