[PATCH] drm/vblank: Tune drm_crtc_accurate_vblank_count() WARN down to a debug

[Ville Syrjala]

From: Ville Syrjälä <ville.syrjala at linux.intel.com>

Since commit 632c6e4edef1 ("drm/vblank: Fix flip event vblank count")
even drivers that don't implement accurate vblank timestamps will end
up using drm_crtc_accurate_vblank_count(). That leads to a WARN every
time drm_crtc_arm_vblank_event() gets called. The could be as often
as every frame for each active crtc.

Considering drm_crtc_accurate_vblank_count() is never any worse than
the drm_vblank_count() we used previously, let's just skip the WARN
unless DRM_UT_VBL is enabled. That way people won't be bothered by
this unless they're debugging vblank code. And let's also change it
to WARN_ONCE() so that even when you're debugging vblank code you
won't get drowned by constant WARNs.

Cc: stable at vger.kernel.org
Cc: Daniel Vetter <daniel at ffwll.ch>
Cc: "Szyprowski, Marek" <m.szyprowski at samsung.com>
Cc: Andrzej Hajda <a.hajda at samsung.com>
Reported-by: Andrzej Hajda <a.hajda at samsung.com>
Fixes: 632c6e4edef1 ("drm/vblank: Fix flip event vblank count")
Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
---
 drivers/gpu/drm/drm_vblank.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
index 13722c373a6a..c81c297995c6 100644
--- a/drivers/gpu/drm/drm_vblank.c
+++ b/drivers/gpu/drm/drm_vblank.c
@@ -299,8 +299,8 @@ u32 drm_crtc_accurate_vblank_count(struct drm_crtc *crtc)
 	u32 vblank;
 	unsigned long flags;
 
-	WARN(!dev->driver->get_vblank_timestamp,
-	     "This function requires support for accurate vblank timestamps.");
+	WARN_ONCE(drm_debug & DRM_UT_VBL && !dev->driver->get_vblank_timestamp,
+		  "This function requires support for accurate vblank timestamps.");
 
 	spin_lock_irqsave(&dev->vblank_time_lock, flags);
 
-- 
2.13.6