Patch "drm/vblank: Tune drm_crtc_accurate_vblank_count() WARN down to a debug" has been added to the 4.14-stable tree

This is a note to let you know that I've just added the patch titled

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

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
drm-vblank-tune-drm_crtc_accurate_vblank_count-warn-down-to-a-debug.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: =?UTF-8?q?Ville=20Syrj=C3=A4l=C3=A4?= <[email protected]>
Date: Mon, 23 Oct 2017 18:25:40 +0300
Subject: drm/vblank: Tune drm_crtc_accurate_vblank_count() WARN down to a debug
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From: Ville Syrjälä <[email protected]>

commit a111fbc4c44d2981f1a8fef64418685be5e30280 upstream.

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.

---
 drivers/gpu/drm/drm_vblank.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

@@ -311,8 +311,8 @@ u32 drm_crtc_accurate_vblank_count(struc
 	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);
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/drm-edid-don-t-send-non-zero-yq-in-avi-infoframe-for-hdmi-1.x-sinks.patch queue-4.14/drm-vblank-fix-flip-event-vblank-count.patch queue-4.14/drm-vblank-tune-drm_crtc_accurate_vblank_count-warn-down-to-a-debug.patch