[PATCH] drm/vblank: Fix flip event vblank count

[Ville Syrjälä]

On Tue, Oct 10, 2017 at 04:33:22PM +0300, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> On machines where the vblank interrupt fires some time after the start
> of vblank (or we just manage to race with the vblank interrupt handler)
> we will currently stuff a stale vblank counter value into the flip event,
> and thus we'll prematurely complete the flip.
> 
> Switch over to drm_crtc_accurate_vblank_count() to make sure we have an
> up to date counter value, crucially also remember to add the +1 so that
> the delayed vblank interrupt won't complete the flip prematurely.
> 
> Cc: stable at vger.kernel.org
> Cc: Daniel Vetter <daniel at ffwll.ch>
> Suggested-by: Daniel Vetter <daniel at ffwll.ch>
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>

Pushed to drm-misc-next with Daniel's irc r-b:
16:48 < danvet> vsyrjala, r-b, I think
...
17:31 < vsyrjala> danvet: your irc r-b for vblank_accurate+1 still
holds?
17:32 < danvet> vsyrjala, yeah

> ---
>  drivers/gpu/drm/drm_vblank.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> index 70f2b9593edc..f14e6c92e332 100644
> --- a/drivers/gpu/drm/drm_vblank.c
> +++ b/drivers/gpu/drm/drm_vblank.c
> @@ -869,7 +869,7 @@ void drm_crtc_arm_vblank_event(struct drm_crtc *crtc,
>  	assert_spin_locked(&dev->event_lock);
>  
>  	e->pipe = pipe;
> -	e->event.sequence = drm_vblank_count(dev, pipe);
> +	e->event.sequence = drm_crtc_accurate_vblank_count(crtc) + 1;
>  	e->event.crtc_id = crtc->base.id;
>  	list_add_tail(&e->base.link, &dev->vblank_event_list);
>  }
> -- 
> 2.13.6

-- 
Ville Syrjälä
Intel OTC