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

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Oct 18, 2017 at 09:07:47AM +0200, Andrzej Hajda wrote:
> Hi Ville,
> 
> On 10.10.2017 15:33, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala@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@vger.kernel.org
> > Cc: Daniel Vetter <daniel@ffwll.ch>
> > Suggested-by: Daniel Vetter <daniel@ffwll.ch>
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >  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;
> 
> With this patch drm_crtc_arm_vblank_event calls
> drm_crtc_accurate_vblank_count, which requires get_vblank_timestamp
> callback, otherwise it issue WARN every time it is called.

Argh! Maybe just remove the WARN then?

> On the other side most of the users of drm_crtc_arm_vblank_event do not
> implement this callback. As a result one can observe multiple WARNs.
> It was observed on Exynos platform but grep shows it can affect many
> other platforms:
> 
> $ git grep -l drm_crtc_arm_vblank_event drivers/gpu/drm/
> drivers/gpu/drm/arm/hdlcd_crtc.c
> drivers/gpu/drm/arm/malidp_drv.c
> drivers/gpu/drm/drm_vblank.c
> drivers/gpu/drm/exynos/exynos_drm_crtc.c
> drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_crtc.c
> drivers/gpu/drm/hisilicon/kirin/kirin_drm_ade.c
> drivers/gpu/drm/i915/intel_sprite.c
> drivers/gpu/drm/imx/ipuv3-crtc.c
> drivers/gpu/drm/mxsfb/mxsfb_crtc.c
> drivers/gpu/drm/nouveau/nouveau_display.c
> drivers/gpu/drm/pl111/pl111_display.c
> drivers/gpu/drm/sti/sti_crtc.c
> drivers/gpu/drm/stm/ltdc.c
> drivers/gpu/drm/sun4i/sun4i_crtc.c
> drivers/gpu/drm/tve200/tve200_display.c
> drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
> drivers/gpu/drm/zte/zx_vou.c
> 
> $ git grep -l get_vblank_timestamp drivers/gpu/drm/
> drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> drivers/gpu/drm/drm_vblank.c
> drivers/gpu/drm/i915/i915_irq.c
> drivers/gpu/drm/msm/mdp/mdp5/mdp5_kms.c
> drivers/gpu/drm/nouveau/nouveau_drm.c
> drivers/gpu/drm/radeon/radeon_drv.c
> drivers/gpu/drm/vc4/vc4_drv.c
> 
> Regards
> Andrzej
> 
> >  	e->event.crtc_id = crtc->base.id;
> >  	list_add_tail(&e->base.link, &dev->vblank_event_list);
> >  }
> 

-- 
Ville Syrjälä
Intel OTC