[Intel-gfx] FBC underruns on GMA4500?

[Jesse Barnes]

On Mon, 09 Aug 2010 19:20:34 +0200
Alexey Fisher <bug-track at fisher-privat.net> wrote:

> On Mo, 2010-08-09 at 09:36 -0700, Jesse Barnes wrote:
> > On Sat, 07 Aug 2010 11:46:19 +0200
> > Alexey Fisher <bug-track at fisher-privat.net> wrote:
> > 
> > > Hallo all,
> > > 
> > > i have some times on my primer desktop with Intel DG45ID board some sort
> > > of flickering, it schort (1 second) and only half of the display. Same
> > > sort of flickering i had with Bug 24314 - [945GME FBC] underruns
> > > followed by freeze after resume with FBC enabled. The difference is - it
> > > will not freeze.
> > > 
> > > If i understand it correctly , it is not normal. But i can't report it,
> > > there is no messages in dmesg or xorg.log
> > 
> > Sounds like potential FIFO underruns, maybe your memory configuration
> > doesn't match the latency we expect in intel_display.c.  You could try
> > increasing the latency constant in that file to see if it makes the
> > flicker go away.
> 
> Can you please point me what file to change? And haw can i check what
> latency is used?

drivers/gpu/drm/i915/intel_display.c, modify (increase) the latency_ns
variable to say 10000.

> > If that helps it's just another example of why we need better latency
> > detection in the driver; unfortunately we don't know how to do that
> > yet...
> 
> Please take a look to this bug:
> https://bugs.freedesktop.org/show_bug.cgi?id=29454
> may be FIFO underrun and hangs have same source.

Yeah repeated underruns can lead to chip hangs.

-- 
Jesse Barnes, Intel Open Source Technology Center