[PATCH 3.19.y-ckt 120/196] drm: Fix treatment of drm_vblank_offdelay in drm_vblank_on() (v2)

From: Kamal Mostafa
Date: Tue Mar 08 2016 - 19:36:03 EST

3.19.8-ckt16 -stable review patch. If anyone has any objections, please let me know.


From: Mario Kleiner <mario.kleiner.de@xxxxxxxxx>

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

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

Signed-off-by: Mario Kleiner <mario.kleiner.de@xxxxxxxxx>
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>

Cc: michel@xxxxxxxxxxx
Cc: vbabka@xxxxxxx
Cc: ville.syrjala@xxxxxxxxxxxxxxx
Cc: daniel.vetter@xxxxxxxx
Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
Cc: alexander.deucher@xxxxxxx
Cc: christian.koenig@xxxxxxx
Signed-off-by: Dave Airlie <airlied@xxxxxxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
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 68193a6..5409518 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -1264,8 +1264,7 @@ 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);