Re: [PATCH 1/4] drm/i915: promote FIFO underruns to DRM_ERROR

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

On Thu, Sep 19, 2013 at 05:20:49PM -0300, Paulo Zanoni wrote:
> 2013/9/19 Chris Wilson <chris@chris-wilson.co.uk>:
> > On Thu, Sep 19, 2013 at 05:00:35PM -0300, Paulo Zanoni wrote:
> >> From: Paulo Zanoni <paulo.r.zanoni@intel.com>
> >>
> >> Linus recently complained about screen corruption when coming out of
> >> DPMS on his Haswell machine, and he also mentioned there were no error
> >> messages on the log. I think I can reproduce this problem, and when it
> >> happens I get a "FIFO underrun" message, but since it's just
> >> DRM_DEBUG_DRIVER it's hard to notice. So promote underruns to error
> >> messages because reports containing "I'm getting a FIFO underrun on
> >> pipe A" are way much better than "I'm getting a screen corruption".
> >
> > Sadly FIFO underruns on quite a few platforms are expected and
> > unfixable. Others they are just expected. We reduced the error level
> > because they are too noisy, and we were not in a position where the
> > underrun was actionable. As we do not yet have the underrun feedback in
> > place, I do not think we are ready for the onslaught of errors.
> >
> > At minimum, you should only set the error message for the platforms you
> > intend to fix.
> 
> Hmmmm, yeah, I should have thought about this a little bit more. Sorry :(
> 
> At least on ILK/SNB/IVB/HSW we have the code to stop flooding dmesg
> and the code to ignore the expected underruns, so I guess a patch
> touching just these platforms would be ok?

I would limit it to HSW before my ILK/SNB/IVB conversion to HSW
watermark code gets in. The current code apparently produces somewhat
incorrect results since according to Imre it even fixes some kind of
rare hang on ILK.

-- 
Ville Syrjälä
Intel OTC