Patch "drm: Fix treatment of drm_vblank_offdelay in drm_vblank_on() (v2)" has been added to the 4.4-stable tree

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

drm: Fix treatment of drm_vblank_offdelay in drm_vblank_on() (v2)

to the 4.4-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-fix-treatment-of-drm_vblank_offdelay-in-drm_vblank_on-v2.patch
and it can be found in the queue-4.4 subdirectory.

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

From: Mario Kleiner <[email protected]>
Date: Fri, 12 Feb 2016 20:30:30 +0100
Subject: drm: Fix treatment of drm_vblank_offdelay in drm_vblank_on() (v2)

From: Mario Kleiner <[email protected]>

commit bb74fc1bf3072bd3ab4ed5f43afd287a63baf2d7 upstream.

drm_vblank_offdelay can have three different types of values:

< 0 is to be always treated the same as dev->vblank_disable_immediate = 0 is to be treated as "never disable vblanks"

that way via dev->vblank_disable_immediate. Otherwise it is a disable timeout in msecs.

This got broken in Linux 3.18+ for the implementation of drm_vblank_on. If the user specified a value of zero which should always reenable vblank irqs in this function, a kms driver could override the users choice by setting vblank_disable_immediate to true. This patch fixes the regression and keeps the user in control.

v2: Only reenable vblank if there are clients left or the user
requested to "never disable vblanks" via offdelay 0. Enabling vblanks even in the "delayed disable" case (offdelay > 0) was specifically added by Ville in commit cd19e52aee922 ("drm: Kick start vblank interrupts at drm_vblank_on()"), but after discussion it turns out that this was done by accident.

Citing Ville: "I think it just ended up as a mess due to changing some of the semantics of offdelay<0 vs. offdelay==0 vs. disable_immediate during the review of the series. So yeah, given how drm_vblank_put() works now, I'd just make this check for offdelay==0."

---
 drivers/gpu/drm/drm_irq.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

@@ -1494,8 +1494,7 @@ void drm_vblank_on(struct drm_device *de
 	 * re-enable interrupts if there are users left, or the
 	 * user wishes vblank interrupts to be enabled all the time.
 	 */
-	if (atomic_read(&vblank->refcount) != 0 ||
-	    (!dev->vblank_disable_immediate && drm_vblank_offdelay == 0))
+	if (atomic_read(&vblank->refcount) != 0 || drm_vblank_offdelay == 0)
 		WARN_ON(drm_vblank_enable(dev, pipe));
 	spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
 }

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

queue-4.4/drm-prevent-vblank-counter-bumps-1-with-active-vblank-clients.-v2.patch queue-4.4/drm-fix-treatment-of-drm_vblank_offdelay-in-drm_vblank_on-v2.patch queue-4.4/drm-nouveau-display-enable-vblank-irqs-after-display-engine-is-on-again.patch queue-4.4/drm-fix-drm_vblank_pre-post_modeset-regression-from-linux-4.4.patch queue-4.4/drm-radeon-don-t-hang-in-radeon_flip_work_func-on-disabled-crtc.-v2.patch queue-4.4/drm-no-op-redundant-calls-to-drm_vblank_off-v2.patch queue-4.4/drm-amdgpu-don-t-hang-in-amdgpu_flip_work_func-on-disabled-crtc.patch