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

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

On Fri, May 25, 2018 at 06:19:17PM +0300, Jani Nikula wrote:
> On Fri, 25 May 2018, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> > 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@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.
> 
> /me .oO( could we wait for the 2nd vblank based on interlace? )

We certainly could. However as explained below we have seen some
similar looking underruns in CI with progressive DP as well, and so
I chose to try the shotgun approach in the hopes of hitting a few
more barn doors.

> 
> >>  
> >> > 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@linux.intel.com>
> >> Acked-by: Chris Wilson <chris@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.
> 
> -- 
> Jani Nikula, Intel Open Source Graphics Center

-- 
Ville Syrjälä
Intel
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