[Intel-gfx] [PATCH 23/29] drm/i915/dp_mst: Enable DSC passthrough

[Imre Deak]

On Fri, Oct 27, 2023 at 05:52:17PM +0300, Ville Syrjälä wrote:
> On Tue, Oct 24, 2023 at 04:09:19AM +0300, Imre Deak wrote:
> > Enable passing through DSC streams to the sink in last branch devices.
> > 
> > Signed-off-by: Imre Deak <imre.deak at intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_dp.c | 26 ++++++++++++++++++++++++-
> >  1 file changed, 25 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> > index a7eb31b489947..bb8951f89f61f 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > @@ -2950,6 +2950,24 @@ intel_dp_sink_set_dsc_decompression(struct intel_connector *connector,
> >  			    str_enable_disable(enable));
> >  }
> >  
> > +static void
> > +intel_dp_sink_set_dsc_passthrough(const struct intel_connector *connector,
> > +				  bool enable)
> > +{
> > +	struct drm_i915_private *i915 = to_i915(connector->base.dev);
> > +	struct drm_dp_aux *aux = connector->port ?
> > +				 connector->port->passthrough_aux : NULL;
> 
> I was worried that we're now setting conflicting compress+passthrough
> bits at the same time, but looks like this magic passthrough_aux thing
> gets sneakily populated by drm_dp_mst_dsc_aux_for_port() whereas the 
> decompression_aux gets just returned directly and tracked by the driver.
> Very confusing.

Yes, probably would be better to have both tracked in connector->port
only.
> 
> But I guess it kinda works

The reason they don't conflict is because a passthrough_aux will be set
only for a DP-to-DP peer branch device if the sink supports this (so not
in a UFP DPCD for instance), in which case decompression_aux will be
NULL. 

> Reviewed-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> > +
> > +	if (!aux)
> > +		return;
> > +
> > +	if (drm_dp_dpcd_writeb(aux, DP_DSC_PASSTHROUGH_EN,
> > +			       enable ? DP_DSC_PASSTHROUGH_EN : 0) < 0)
> > +		drm_dbg_kms(&i915->drm,
> > +			    "Failed to %s sink compression passthrough state\n",
> > +			    str_enable_disable(enable));
> > +}
> > +
> >  void intel_dp_sink_set_decompression_state(struct intel_connector *connector,
> >  					   const struct intel_crtc_state *crtc_state,
> >  					   bool enable)
> > @@ -2962,7 +2980,13 @@ void intel_dp_sink_set_decompression_state(struct intel_connector *connector,
> >  	if (drm_WARN_ON(&i915->drm, !connector->dp.dsc_decompression_aux))
> >  		return;
> >  
> > -	intel_dp_sink_set_dsc_decompression(connector, enable);
> > +	if (enable) {
> > +		intel_dp_sink_set_dsc_passthrough(connector, true);
> > +		intel_dp_sink_set_dsc_decompression(connector, true);
> > +	} else {
> > +		intel_dp_sink_set_dsc_decompression(connector, false);
> > +		intel_dp_sink_set_dsc_passthrough(connector, false);
> > +	}
> >  }
> >  
> >  static void
> > -- 
> > 2.39.2
> 
> -- 
> Ville Syrjälä
> Intel