[PATCH 2/3] drm: Skip the waitqueue setup for vblank queries

[Chris Wilson]

Avoid adding to the waitqueue and reprobing the current vblank if the
caller is only querying the current vblank sequence and timestamp, where
we know that the wait would return immediately.

v2: Add CRTC identifier to debug messages

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Cc: Daniel Vetter <daniel at ffwll.ch>
Cc: Michel Dänzer <michel at daenzer.net>
Cc: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
Cc: Dave Airlie <airlied at redhat.com>,
Cc: Mario Kleiner <mario.kleiner.de at gmail.com>
Reviewed-by: Michel Dänzer <michel at daenzer.net>
Reviewed-and-tested-by: Mario Kleiner <mario.kleiner.de at gmail.com>
---
 drivers/gpu/drm/drm_irq.c | 26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index ca5ef87c57c1..866cf58a36c5 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -1710,7 +1710,7 @@ int drm_wait_vblank(struct drm_device *dev, void *data,
 
 	ret = drm_vblank_get(dev, pipe);
 	if (ret) {
-		DRM_DEBUG("failed to acquire vblank counter, %d\n", ret);
+		DRM_DEBUG("crtc %d failed to acquire vblank counter, %d\n", pipe, ret);
 		return ret;
 	}
 	seq = drm_vblank_count(dev, pipe);
@@ -1738,14 +1738,16 @@ int drm_wait_vblank(struct drm_device *dev, void *data,
 		vblwait->request.sequence = seq + 1;
 	}
 
-	DRM_DEBUG("waiting on vblank count %d, crtc %u\n",
-		  vblwait->request.sequence, pipe);
-	vblank->last_wait = vblwait->request.sequence;
-	DRM_WAIT_ON(ret, vblank->queue, 3 * HZ,
-		    (((drm_vblank_count(dev, pipe) -
-		       vblwait->request.sequence) <= (1 << 23)) ||
-		     !vblank->enabled ||
-		     !dev->irq_enabled));
+	if (vblwait->request.sequence != seq) {
+		DRM_DEBUG("waiting on vblank count %d, crtc %u\n",
+			  vblwait->request.sequence, pipe);
+		vblank->last_wait = vblwait->request.sequence;
+		DRM_WAIT_ON(ret, vblank->queue, 3 * HZ,
+			    (((drm_vblank_count(dev, pipe) -
+			       vblwait->request.sequence) <= (1 << 23)) ||
+			     !vblank->enabled ||
+			     !dev->irq_enabled));
+	}
 
 	if (ret != -EINTR) {
 		struct timeval now;
@@ -1754,10 +1756,10 @@ int drm_wait_vblank(struct drm_device *dev, void *data,
 		vblwait->reply.tval_sec = now.tv_sec;
 		vblwait->reply.tval_usec = now.tv_usec;
 
-		DRM_DEBUG("returning %d to client\n",
-			  vblwait->reply.sequence);
+		DRM_DEBUG("crtc %d returning %d to client\n",
+			  pipe, vblwait->reply.sequence);
 	} else {
-		DRM_DEBUG("vblank wait interrupted by signal\n");
+		DRM_DEBUG("crtc %d vblank wait interrupted by signal\n", pipe);
 	}
 
 done:
-- 
2.7.0.rc3