[Intel-gfx] [PATCH 1/2] drm/i915: Try to suppress more spurious PCH underruns on ILK-IVB

[Ville Syrjälä]

On Thu, May 24, 2018 at 10:19:02PM +0100, Chris Wilson wrote:
> Quoting Ville Syrjala (2018-05-24 20:04:05)
> > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > 
> > My ILK seems to generate a spurious PCH underrun with most interlaced
> > HDMI modes. Add a second vblank wait to avoid it.
> 
> Fwiw, a second vblank because of interlacing is very believable.
>  
> > We have seen some spurious PCH underruns still in CI as well, some
> > of which seem to be progressive DP. The logs also point towards some
> > spurious underrins with progressive HDMI on SNB. While I don't have
> > a solid explanation for those let's try to kill all the birds with one
> > stone and always do the double wait.
> > 
> > Buzilla: https://bugs.freedesktop.org/show_bug.cgi?id=106387
> > Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Acked-by: Chris Wilson <chris at chris-wilson.co.uk>a

Thanks. Pushed to dinq.

> 
> No point waiting for a vblank worker? ;)

That might take a while. Also I'm not sure we'd want to use it here
because we'd probably want underrun reporting to be active by the
time we enable the planes. So we'd either have to enable planes from
the worker as well, or we'd just sample the vblank counter at the
end of crtc_enable and wait for n+2 just before we start to enable the
planes. Not sure if that latter approach would gain us any practical
parallelism though.

-- 
Ville Syrjälä
Intel