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>

3 files changed, 13 insertions, 5 deletions

diff --git a/drivers/gpu/drm/rcar-du/rcar_du_crtc.c b/drivers/gpu/drm/rcar-du/rcar_du_crtc.c
index 6e5bd0b92dfa..301ea1a8018e 100644
--- a/drivers/gpu/drm/rcar-du/rcar_du_crtc.c
+++ b/drivers/gpu/drm/rcar-du/rcar_du_crtc.c
@@ -690,6 +690,7 @@ static int rcar_du_crtc_enable_vblank(struct drm_crtc *crtc)
 
 	rcar_du_crtc_write(rcrtc, DSRCR, DSRCR_VBCL);
 	rcar_du_crtc_set(rcrtc, DIER, DIER_VBE);
+	rcrtc->vblank_enable = true;
 
 	return 0;
 }
@@ -699,6 +700,7 @@ static void rcar_du_crtc_disable_vblank(struct drm_crtc *crtc)
 	struct rcar_du_crtc *rcrtc = to_rcar_crtc(crtc);
 
 	rcar_du_crtc_clr(rcrtc, DIER, DIER_VBE);
+	rcrtc->vblank_enable = false;
 }
 
 static const struct drm_crtc_funcs crtc_funcs = {
@@ -743,10 +745,10 @@ static irqreturn_t rcar_du_crtc_irq(int irq, void *arg)
 	spin_unlock(&rcrtc->vblank_lock);
 
 	if (status & DSSR_VBK) {
-		drm_crtc_handle_vblank(&rcrtc->crtc);
-
-		if (rcdu->info->gen < 3)
+		if (rcdu->info->gen < 3) {
+			drm_crtc_handle_vblank(&rcrtc->crtc);
 			rcar_du_crtc_finish_page_flip(rcrtc);
+		}
 
 		ret = IRQ_HANDLED;
 	}
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;
 
diff --git a/drivers/gpu/drm/rcar-du/rcar_du_vsp.c b/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
index e43b065e141a..6de6be3d9090 100644
--- a/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
+++ b/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
@@ -31,11 +31,15 @@
 #include "rcar_du_kms.h"
 #include "rcar_du_vsp.h"
 
-static void rcar_du_vsp_complete(void *private)
+static void rcar_du_vsp_complete(void *private, bool completed)
 {
 	struct rcar_du_crtc *crtc = private;
 
-	rcar_du_crtc_finish_page_flip(crtc);
+	if (crtc->vblank_enable)
+		drm_crtc_handle_vblank(&crtc->crtc);
+
+	if (completed)
+		rcar_du_crtc_finish_page_flip(crtc);
 }
 
 void rcar_du_vsp_enable(struct rcar_du_crtc *crtc)