From 82c8e025b577a4b9b87fbbc2a1c4dd401e3a2521 Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Wed, 15 Mar 2017 20:40:26 +0000
Subject: [PATCH] drm: Skip the waitqueue setup for vblank queries
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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@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Michel Dänzer <michel@daenzer.net>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Dave Airlie <airlied@redhat.com>,
Cc: Mario Kleiner <mario.kleiner.de@gmail.com>
Reviewed-by: Michel Dänzer <michel@daenzer.net>
Reviewed-and-tested-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20170315204027.20160-2-chris@chris-wilson.co.uk
---
 drivers/gpu/drm/drm_irq.c | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index e64b05ea95ea..53a526c7b24d 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -1610,7 +1610,7 @@ 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);
@@ -1638,13 +1638,15 @@ int drm_wait_vblank(struct drm_device *dev, void *data,
 		return drm_queue_vblank_event(dev, pipe, vblwait, file_priv);
 	}
 
-	DRM_DEBUG("waiting on vblank count %u, crtc %u\n",
-		  vblwait->request.sequence, pipe);
-	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 %u, crtc %u\n",
+			  vblwait->request.sequence, pipe);
+		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;
@@ -1653,10 +1655,10 @@ 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 %u to client\n",
-			  vblwait->reply.sequence);
+		DRM_DEBUG("crtc %d returning %u 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:
-- 
2.20.1