Re: [PATCH 1/6] drm/i915/psr: Avoid DPCD reads when panel does not support PSR

[Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>]

On Thu, 2018-05-17 at 17:27 -0700, Tarun Vyas wrote:
> On Fri, May 11, 2018 at 12:51:40PM -0700, Dhinakaran Pandiyan wrote:
> > 
> > Ville noticed that we are unncessarily reading DPCD's after knowing
> > panel did not support PSR. Looks like this check that was present
> > earlier got removed unintentionally, let's put it back.
> > 
> > While we do this, add the PSR version number in the debug print.
> > 
> > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_psr.c | 14 ++++++++------
> >  1 file changed, 8 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_psr.c
> > b/drivers/gpu/drm/i915/intel_psr.c
> > index db27f2faa1de..8fe6d2f9ab2b 100644
> > --- a/drivers/gpu/drm/i915/intel_psr.c
> > +++ b/drivers/gpu/drm/i915/intel_psr.c
> > @@ -250,10 +250,12 @@ void intel_psr_init_dpcd(struct intel_dp
> > *intel_dp)
> >  	drm_dp_dpcd_read(&intel_dp->aux, DP_PSR_SUPPORT, intel_dp-
> > >psr_dpcd,
> >  			 sizeof(intel_dp->psr_dpcd));
> >  
> > -	if (intel_dp->psr_dpcd[0]) {
> > -		dev_priv->psr.sink_support = true;
> > -		DRM_DEBUG_KMS("Detected EDP PSR Panel.\n");
> > -	}
> > +	if (!intel_dp->psr_dpcd[0])
> > +		return;
> > +
> > +	DRM_DEBUG_KMS("eDP panel supports PSR version %x\n",
> > +		      intel_dp->psr_dpcd[0]);
> > +	dev_priv->psr.sink_support = true;
> >  
> >  	if (INTEL_GEN(dev_priv) >= 9 &&
> >  	    (intel_dp->psr_dpcd[0] ==
> > DP_PSR2_WITH_Y_COORD_IS_SUPPORTED)) {
> > @@ -270,8 +272,8 @@ void intel_psr_init_dpcd(struct intel_dp
> > *intel_dp)
> >  		 */
> >  		dev_priv->psr.sink_psr2_support =
> >  				intel_dp_get_y_coord_required(inte
> > l_dp);
> > -		DRM_DEBUG_KMS("PSR2 %s on sink", dev_priv-
> > >psr.sink_psr2_support
> > -			      ? "supported" : "not supported");
> > +		DRM_DEBUG_KMS("PSR2 %ssupported\n",
> > +			      dev_priv->psr.sink_psr2_support ? ""
> > : "not ");
> Would it make sense to make it clearer that PSR2 is not supported b/c
> of lack of y-coordinate support on the sink ?

We could do something like 

dev_priv->psr.sink_psr2_support = y_req && alpm;
DRM_DEBUG_KMS("PSR2 %ssupported ALPM %d Y-req %d\n",
              dev_priv->psr.sink_psr2_support ? "" : "not ",
              alpm, y_req);

But this would need the code movement done in patch 6/6.


> 
> Reviewed-by: Tarun Vyas <tarun.vyas@intel.com>
> > 
> >  
> >  		if (dev_priv->psr.sink_psr2_support) {
> >  			dev_priv->psr.colorimetry_support =
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