Re: [Intel-gfx] [PATCH 20/20] drm/i915/dp: Disable DFP RGB->YCbCr conversion for now

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Oct 27, 2021 at 12:57:37PM +0530, Nautiyal, Ankit K wrote:
> 
> On 10/15/2021 7:09 PM, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >
> > We lack sufficient state tracking to figure out whether
> > we want the DFP to perform the RGB->YCbCr conversion for us
> > or not. So currently we are blindly just enabling that all the
> > time when supported by the DFP. That is nonsense. So until
> > we imporve our state tracking for this just disable the feature.
> >
> > Cc: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
> > Cc: Uma Shankar <uma.shankar@intel.com>
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >   drivers/gpu/drm/i915/display/intel_dp.c | 10 ++++++++++
> >   1 file changed, 10 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> > index 29b12456c461..3e2a29b589a9 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > @@ -1107,6 +1107,7 @@ static bool intel_dp_supports_dsc(struct intel_dp *intel_dp,
> >   static bool intel_dp_is_ycbcr420(struct intel_dp *intel_dp,
> >   				 const struct intel_crtc_state *crtc_state)
> >   {
> > +	/* FIXME see intel_dp_update_420() regarding rgb_to_ycbcr */
> >   	return crtc_state->output_format == INTEL_OUTPUT_FORMAT_YCBCR420 ||
> >   		(crtc_state->output_format == INTEL_OUTPUT_FORMAT_YCBCR444 &&
> >   		 intel_dp->dfp.ycbcr_444_to_420);
> > @@ -2456,6 +2457,7 @@ void intel_dp_configure_protocol_converter(struct intel_dp *intel_dp,
> >   			    "Failed to %s protocol converter YCbCr 4:2:0 conversion mode\n",
> >   			    enabledisable(intel_dp->dfp.ycbcr_444_to_420));
> >   
> > +	/* FIXME see intel_dp_update_420() regarding rgb_to_ycbcr */
> >   	tmp = intel_dp->dfp.rgb_to_ycbcr ?
> >   		DP_CONVERSION_BT709_RGB_YCBCR_ENABLE : 0;
> >   
> > @@ -4261,6 +4263,14 @@ intel_dp_update_420(struct intel_dp *intel_dp)
> >   	rgb_to_ycbcr = drm_dp_downstream_rgb_to_ycbcr_conversion(intel_dp->dpcd,
> >   								 intel_dp->downstream_ports,
> >   								 DP_DS_HDMI_BT709_RGB_YCBCR_CONV);
> > +	/*
> > +	 * FIXME need to actually track whether we're really
> > +	 * going to be doing the RGB->YCbCr connversion or not.
> > +	 * We can't tell by simply looking at intel_dp->dfp.rgb_to_ycbcr.
> > +	 * Readout is going to annoying due to having to read that
> > +	 * state from external hardware that may vanish at any time :(
> > +	 */
> 
> 
> Hmm right. Do you have any suggestion what should be the better place 
> for defining the policy for using DFPs CSC or use our own HW, in case of 
> YCbCr 420 output?

One idea that came to mind was just adding some kind of
sink_format thing into the crtc_state, and computing that appropriately
during .compute_config(). But as mentioned the readout part is going to
be annoying. Maybe we just won't have readout for it.

-- 
Ville Syrjälä
Intel