Re: [PATCH 7/7] drm/i915: Dont -ETIMEDOUT on identical new and previous (count, crc).

[Rafael Antognolli <rafael.antognolli@intel.com>]

On Wed, Jul 29, 2015 at 10:26:53AM +0200, Daniel Vetter wrote:
> On Tue, Jul 28, 2015 at 10:05:21PM +0000, Vivi, Rodrigo wrote:
> > On Tue, 2015-07-28 at 13:25 -0700, Rafael Antognolli wrote:
> > > On Thu, Jul 23, 2015 at 04:35:50PM -0700, Rodrigo Vivi wrote:
> > > > By Vesa DP 1.2 spec TEST_CRC_COUNT is a "4 bit wrap counter which
> > > > increments each time the TEST_CRC_x_x are updated."
> > > > 
> > > > However if we are trying to verify the screen hasn't changed we get
> > > > same (count, crc) pair twice. Without this patch we would return
> > > > -ETIMEOUT in this case.
> > > > 
> > > > So, if in 6 vblanks the pair (count, crc) hasn't changed we
> > > > return it anyway instead of returning error and let test case decide
> > > > if it was right or not.
> > > > 
> > > > Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
> > > 
> > > Looks good.
> > > 
> > > > ---
> > > >  drivers/gpu/drm/i915/intel_dp.c | 21 +++++++++++++++------
> > > >  1 file changed, 15 insertions(+), 6 deletions(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > > > index c7372a1..e99ec7a 100644
> > > > --- a/drivers/gpu/drm/i915/intel_dp.c
> > > > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > > > @@ -4028,6 +4028,7 @@ int intel_dp_sink_crc(struct intel_dp *intel_dp, u8 *crc)
> > > >  	u8 buf;
> > > >  	int count, ret;
> > > >  	int attempts = 6;
> > > > +	bool old_equal_new;
> > > >  
> > > >  	ret = intel_dp_sink_crc_start(intel_dp);
> > > >  	if (ret)
> > > > @@ -4042,6 +4043,7 @@ int intel_dp_sink_crc(struct intel_dp *intel_dp, u8 *crc)
> > > >  			goto stop;
> > > >  		}
> > > >  		count = buf & DP_TEST_COUNT_MASK;
> > > > +
> > > >  		/*
> > > >  		 * Count might be reset during the loop. In this case
> > > >  		 * last known count needs to be reset as well.
> > > > @@ -4053,17 +4055,24 @@ int intel_dp_sink_crc(struct intel_dp *intel_dp, u8 *crc)
> > > >  			ret = -EIO;
> > > >  			goto stop;
> > > >  		}
> > > > -	} while (--attempts && (count == 0 || (count == intel_dp->sink_crc.last_count &&
> > > > -					       !memcmp(intel_dp->sink_crc.last_crc, crc,
> > > > -						       6 * sizeof(u8)))));
> > > > +
> > > > +		old_equal_new = (count == intel_dp->sink_crc.last_count &&
> > > > +				 !memcmp(intel_dp->sink_crc.last_crc, crc,
> > > > +					 6 * sizeof(u8)));
> > > > +
> > > > +	} while (--attempts && (count == 0 || old_equal_new));
> > > >  
> > > >  	intel_dp->sink_crc.last_count = buf & DP_TEST_COUNT_MASK;
> > > >  	memcpy(intel_dp->sink_crc.last_crc, crc, 6 * sizeof(u8));
> > > >  
> > > >  	if (attempts == 0) {
> > > > -		DRM_DEBUG_KMS("Panel is unable to calculate CRC after 6 vblanks\n");
> > > > -		ret = -ETIMEDOUT;
> > > > -		goto stop;
> > > > +		if (old_equal_new) {
> > > > +			DRM_DEBUG_KMS("Unreliable Sink CRC counter: Current returned CRC is identical to the previous one\n");
> > > 
> > > Isn't this line a little too long?
> > 
> > I agree, but I had no idea how to make it shorter. I believe this long
> > debug message is the only case where we can go over 80 characters in
> > i915. but if it isn't true and/or have a suggestion how to make it
> > shorter please let me know that I can change.
> 
> dmesg output is explicitly an exception since breaking lines makes it much
> harder to grep for a line you spot in dmesg. Ofc 500 lines would be a bit
> too much, we're breaking those. But this one here is totally fine.

Nice, I never thought about being able to grep, but makes total sense.

> Remember, checkpatch is just suggestions mostly, not law.

I wasn't aware of it, but good to know that it exists. I'll check it out.

Reviewed-by: Rafael Antognolli <rafael.antognolli@intel.com>

> > 
> > > 
> > > > +		} else {
> > > > +			DRM_ERROR("Panel is unable to calculate any CRC after 6 vblanks\n");
> > > > +			ret = -ETIMEDOUT;
> > > > +			goto stop;
> > > > +		}
> > > >  	}
> > > >  
> > > >  stop:
> > > > -- 
> > > > 2.1.0
> > > > 
> > > > _______________________________________________
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> > 
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> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
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