[Intel-gfx] [PATCH 1/5] drm/vblank: Fix return type for drm_vblank_count()

[Pandiyan, Dhinakaran]

On Mon, 2018-01-15 at 10:38 +0100, Daniel Vetter wrote:
> On Fri, Jan 12, 2018 at 01:57:03PM -0800, Dhinakaran Pandiyan wrote:
> > drm_vblank_count() has a u32 type returning what is a 64-bit vblank count.
> > The effect of this is when drm_wait_vblank_ioctl() tries to widen the user
> > space requested vblank sequence using this clipped 32-bit count(when the
> > value is >= 2^32) as reference, the requested sequence remains a 32-bit
> > value and gets queued like that. However, the code that checks if the
> > requested sequence has passed compares this against the 64-bit vblank
> > count.
> > 
> > Cc: Keith Packard <keithp at keithp.com>
> > Cc: Michel Dänzer <michel at daenzer.net>
> > Cc: Daniel Vetter <daniel at ffwll.ch>
> > Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
> 
> Sounds like the 64bit widening wasn't all that well tested ... do we have
> an igt for this? Iirc the base igt was merged already.

I don't see anything that would particularly trigger this condition
i.e., vblank->count > 2^32 in the IGTs. We'll need to implement
something to force set a very large vblank->count and then request a
vblank sequence.




> -Daniel
> 
> > ---
> >  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 32d9bcf5be7f..768a8e44d99b 100644
> > --- a/drivers/gpu/drm/drm_vblank.c
> > +++ b/drivers/gpu/drm/drm_vblank.c
> > @@ -271,7 +271,7 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
> >  	store_vblank(dev, pipe, diff, t_vblank, cur_vblank);
> >  }
> >  
> > -static u32 drm_vblank_count(struct drm_device *dev, unsigned int pipe)
> > +static u64 drm_vblank_count(struct drm_device *dev, unsigned int pipe)
> >  {
> >  	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
> >  
> > -- 
> > 2.11.0
> > 
>