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

[Jani Nikula <jani.nikula@linux.intel.com>]

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 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
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