Re: [PATCH 1/1] drm/i915: skip the second CRC even for GEN 7 GPUs

["Chegondi, Harish" <harish.chegondi@intel.com>]

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On Thu, 2019-05-16 at 15:55 +0300, Jani Nikula wrote:
> On Thu, 16 May 2019, Maarten Lankhorst <
> maarten.lankhorst@linux.intel.com> wrote:
> > Op 16-05-2019 om 07:58 schreef Harish Chegondi:
> > > display_pipe_crc_irq_handler() skips the first CRC for all GPUs
> > > and the
> > > second CRC for GEN8+ GPUs. The second CRC is invalid even for BYT
> > > which
> > > is a GEN7 GPU. So, skip the second CRC even for GEN7 GPUs.
> > > 
> > > Cc: Jani Nikula <jani.nikula@intel.com>
> > > Cc: Tomi Sarvela <tomi.p.sarvela@intel.com>
> > > Cc: Petri Latvala <petri.latvala@intel.com>
> > > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> > > Signed-off-by: Harish Chegondi <harish.chegondi@intel.com>
> > > References: https://bugs.freedesktop.org/show_bug.cgi?id=103191
> > > ---
> > >  drivers/gpu/drm/i915/i915_irq.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/i915_irq.c
> > > b/drivers/gpu/drm/i915/i915_irq.c
> > > index 233211fde0ea..3809e9f7fae2 100644
> > > --- a/drivers/gpu/drm/i915/i915_irq.c
> > > +++ b/drivers/gpu/drm/i915/i915_irq.c
> > > @@ -1775,11 +1775,11 @@ static void
> > > display_pipe_crc_irq_handler(struct drm_i915_private *dev_priv,
> > >  	 * bonkers. So let's just wait for the next vblank and read
> > >  	 * out the buggy result.
> > >  	 *
> > > -	 * On GEN8+ sometimes the second CRC is bonkers as well, so
> > > +	 * On GEN7+ sometimes the second CRC is bonkers as well, so
> > >  	 * don't trust that one either.
> > >  	 */
> > >  	if (pipe_crc->skipped <= 0 ||
> > > -	    (INTEL_GEN(dev_priv) >= 8 && pipe_crc->skipped == 1)) {
> > > +	    (INTEL_GEN(dev_priv) >= 7 && pipe_crc->skipped == 1)) {
> > >  		pipe_crc->skipped++;
> > >  		spin_unlock(&pipe_crc->lock);
> > >  		return;
> > 
> > I would be interested in the results, haswell is different from
> > VLV. Has it ever been observed on that platform?
> 
> Good point. I looked at [1] which I presumed was on VLV, but it says
> nothing about HSW.

In fdo # 103191, CRC mismatch failures in igt@kms_pipe_crc_basic@*
tests have not been observed on HSW. These tests have been very
consistently failing on CI fi-byt-squawks system which is a chromebook,
sporadically failing on CI fi-byt-clapper system which is also a
chromebook. However the tests are passing on other CI BYT systems like
fi-byt-n2820 and fi-byt-j1900 which are not chromebooks and the display
is not eDP. I haven't seen these failures happening on other GEN7 GPUs.
Instead of skipping the second CRC just for BYT, I thought it may be a
better idea to skip the second CRC on all GEN7 GPUs as the current code
is already skipping the second CRC on all GEN8+ GPUs.

Thanks!
Harish.

> 
> BR,
> Jani.
> 
> 
> 
> [1] https://bugs.freedesktop.org/show_bug.cgi?id=103191#c34
> 
> 

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