linux-kernel - [PATCH 4.2.y-ckt 170/273] drm: Fix treatment of drm_vblank_offdelay in drm_vblank

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Message-Id: <1457391064-6660-171-git-send-email-kamal@canonical.com>
Date:	Mon,  7 Mar 2016 14:49:21 -0800
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Mario Kleiner <mario.kleiner.de@...il.com>, michel@...nzer.net,
	vbabka@...e.cz, ville.syrjala@...ux.intel.com,
	daniel.vetter@...ll.ch, dri-devel@...ts.freedesktop.org,
	alexander.deucher@....com, christian.koenig@....com,
	Dave Airlie <airlied@...hat.com>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 4.2.y-ckt 170/273] drm: Fix treatment of drm_vblank_offdelay in drm_vblank_on() (v2)

4.2.8-ckt5 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Mario Kleiner <mario.kleiner.de@...il.com>

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"
> 0 is to be treated as disable immediate if kms driver wants it
    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."

Signed-off-by: Mario Kleiner <mario.kleiner.de@...il.com>
Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>

Cc: michel@...nzer.net
Cc: vbabka@...e.cz
Cc: ville.syrjala@...ux.intel.com
Cc: daniel.vetter@...ll.ch
Cc: dri-devel@...ts.freedesktop.org
Cc: alexander.deucher@....com
Cc: christian.koenig@....com
Signed-off-by: Dave Airlie <airlied@...hat.com>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 drivers/gpu/drm/drm_irq.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index b50fa0a..6447b48 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -1338,8 +1338,7 @@ void drm_vblank_on(struct drm_device *dev, int crtc)
 	 * 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, crtc));
 	spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
 }
-- 
2.7.0