Re: [PATCH] drm/i915: Wait for vblank after register read

[Mika Kahola <mika.kahola@intel.com>]

On Thu, 2018-04-19 at 17:09 +0300, Jani Nikula wrote:
> On Wed, 18 Apr 2018, Mika Kahola <mika.kahola@intel.com> wrote:
> > 
> > When reading out CRC's we  wait for a vblank on
> > intel_dp_sink_crc_start()
> > function. When we start reading out CRC's in intel_dp_sink_crc()
> > loop we
> > first wait for a vblank yielding that all in all we end up waiting
> > two
> > vblanks on the first iteration round. Therefore, let's move the
> > intel_wait_for_vblank() as the last routine that we do in an
> > iteration loop
> > in intel_dp_sink_crc().
> > 
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103166
> Umm, do the CI failures in the bug really use sink crc, or are they
> rather about pipe crc?
> 
The bug is more on pipe crc. This just caught my attention while I was
looking into these bugs. 

Was there a reason why we need to wait two vblanks here before running
the loop?

> BR,
> Jani.
> 
> 
> > 
> > Signed-off-by: Mika Kahola <mika.kahola@intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_dp.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_dp.c
> > b/drivers/gpu/drm/i915/intel_dp.c
> > index 62f82c4..6eb97fa 100644
> > --- a/drivers/gpu/drm/i915/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > @@ -3972,13 +3972,14 @@ int intel_dp_sink_crc(struct intel_dp
> > *intel_dp, struct intel_crtc_state *crtc_s
> >  		return ret;
> >  
> >  	do {
> > -		intel_wait_for_vblank(dev_priv, intel_crtc->pipe);
> > -
> >  		if (drm_dp_dpcd_readb(&intel_dp->aux,
> >  				      DP_TEST_SINK_MISC, &buf) <
> > 0) {
> >  			ret = -EIO;
> >  			goto stop;
> >  		}
> > +
> > +		intel_wait_for_vblank(dev_priv, intel_crtc->pipe);
> > +
> >  		count = buf & DP_TEST_COUNT_MASK;
> >  
> >  	} while (--attempts && count == 0);
-- 
Mika Kahola - Intel OTC

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