[Intel-gfx] [PATCH] drm/i915: Only enable DFP 4:4:4->4:2:0 conversion when outputting YCbCr 4:4:4

[Ville Syrjälä]

On Thu, Jan 14, 2021 at 09:27:35AM +0200, Jani Nikula wrote:
> On Mon, 11 Jan 2021, Ville Syrjala <ville.syrjala at linux.intel.com> wrote:
> > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> >
> > Let's not enable the 4:4:4->4:2:0 conversion bit in the DFP unless we're
> > actually outputting YCbCr 4:4:4. It would appear some protocol
> > converters blindy consult this bit even when the source is outputting
> > RGB, resulting in a visual mess.
> >
> > Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2914
> > Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> Fixes: 181567aa9f0d ("drm/i915: Do YCbCr 444->420 conversion via DP protocol converters")
> Cc: <stable at vger.kernel.org> # v5.10+
> 
> Right?

Not sure I should to add the stable tag directly since it apparently
applies cleanly but does not build. So needs a custom backport.

> 
> Reviewed-by: Jani Nikula <jani.nikula at intel.com>

Ta.

> 
> > ---
> >  drivers/gpu/drm/i915/display/intel_dp.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> > index 4f190a82d4ad..aa30ef9f6906 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > @@ -4368,8 +4368,8 @@ void intel_dp_configure_protocol_converter(struct intel_dp *intel_dp,
> >  		drm_dbg_kms(&i915->drm, "Failed to set protocol converter HDMI mode to %s\n",
> >  			    enableddisabled(intel_dp->has_hdmi_sink));
> >  
> > -	tmp = intel_dp->dfp.ycbcr_444_to_420 ?
> > -		DP_CONVERSION_TO_YCBCR420_ENABLE : 0;
> > +	tmp = crtc_state->output_format == INTEL_OUTPUT_FORMAT_YCBCR444 &&
> > +		intel_dp->dfp.ycbcr_444_to_420 ? DP_CONVERSION_TO_YCBCR420_ENABLE : 0;
> >  
> >  	if (drm_dp_dpcd_writeb(&intel_dp->aux,
> >  			       DP_PROTOCOL_CONVERTER_CONTROL_1, tmp) != 1)
> 
> -- 
> Jani Nikula, Intel Open Source Graphics Center

-- 
Ville Syrjälä
Intel