Re: [PATCH 4/9] drm/i915/dp: Restructure the sink/output format selection

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

On Mon, Apr 06, 2026 at 11:02:03AM +0530, Nautiyal, Ankit K wrote:
> 
> On 3/31/2026 7:05 PM, Nicolas Frattaroli wrote:
> > On Tuesday, 31 March 2026 01:53:34 Central European Summer Time Ville Syrjala wrote:
> >> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >>
> >> Restructure intel_dp_compute_output_format() to resemble the new
> >> intel_hdmi_compute_output_formats().
> >>
> >> Again, we basically have two main code paths:
> >> - YCbCr 4:2:0 only modes
> >> - everything else including YCbCr 4:2:0 also modes
> >>
> >> Take the exact same approach with the DP code, making the
> >> format selection much less convoluted.
> >>
> >> Cc: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
> >> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >> ---
> >>   drivers/gpu/drm/i915/display/intel_dp.c | 98 +++++++++++++++++--------
> >>   1 file changed, 69 insertions(+), 29 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> >> index 4955bd8b11d7..230b45acde29 100644
> >> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> >> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> >> @@ -1371,6 +1371,28 @@ intel_dp_mode_valid_downstream(struct intel_connector *connector,
> >>   	return MODE_OK;
> >>   }
> >>   
> >> +static enum drm_mode_status
> >> +intel_dp_sink_format_valid(struct intel_connector *connector,
> >> +			   const struct drm_display_mode *mode,
> >> +			   enum intel_output_format sink_format)
> >> +{
> >> +	const struct drm_display_info *info = &connector->base.display_info;
> >> +
> >> +	switch (sink_format) {
> >> +	case INTEL_OUTPUT_FORMAT_YCBCR420:
> >> +		if (!connector->base.ycbcr_420_allowed ||
> >> +		    !drm_mode_is_420(info, mode))
> >> +			return MODE_NO_420;
> >> +
> >> +		return MODE_OK;
> >> +	case INTEL_OUTPUT_FORMAT_RGB:
> >> +		return MODE_OK;
> >> +	default:
> >> +		MISSING_CASE(sink_format);
> >> +		return MODE_BAD;
> >> +	}
> >> +}
> >> +
> > I think here we'll want another
> > ---
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> > index e23162fc3f8b..a1dc089c54f5 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > @@ -1373,6 +1373,11 @@ intel_dp_sink_format_valid(struct intel_connector *connector,
> >   
> >                  return MODE_OK;
> >          case INTEL_OUTPUT_FORMAT_RGB:
> > +               return MODE_OK;
> > +       case INTEL_OUTPUT_FORMAT_YCBCR444:
> > +               if (!(info->color_formats & BIT(DRM_OUTPUT_COLOR_FORMAT_YCBCR444)))
> > +                       return MODE_BAD;
> > +
> >                  return MODE_OK;
> >          default:
> >                  MISSING_CASE(sink_format);
> > ---
> >
> > though this time, no bpc related changes. With that fixed, I get
> > YCbCr444 at 10bpc as well as 8bpc. Can't test 4:2:0 for what appears
> > to be unrelated userspace reasons, though the KMS property's enum
> > value is exposed properly.
> 
> 
> Hmm... this alone should not be sufficient till we actually have code to 
> try with YCBCR444 in intel_dp_compute_formats().
> 
> 
> >
> >>   int intel_dp_max_hdisplay_per_pipe(struct intel_display *display)
> >>   {
> >>   	return DISPLAY_VER(display) >= 30 ? 6144 : 5120;
> >> @@ -3330,41 +3352,59 @@ static int
> >>   intel_dp_compute_output_format(struct intel_encoder *encoder,
> >>   			       struct intel_crtc_state *crtc_state,
> >>   			       struct drm_connector_state *conn_state,
> >> -			       bool respect_downstream_limits)
> >> +			       bool respect_downstream_limits,
> >> +			       enum intel_output_format sink_format)
> >>   {
> >> -	struct intel_display *display = to_intel_display(encoder);
> >>   	struct intel_dp *intel_dp = enc_to_intel_dp(encoder);
> >>   	struct intel_connector *connector = intel_dp->attached_connector;
> >> -	const struct drm_display_info *info = &connector->base.display_info;
> >>   	const struct drm_display_mode *adjusted_mode = &crtc_state->hw.adjusted_mode;
> >> -	bool ycbcr_420_only;
> >> -	int ret;
> >>   
> >> -	ycbcr_420_only = drm_mode_is_420_only(info, adjusted_mode);
> >> -
> >> -	if (ycbcr_420_only && !connector->base.ycbcr_420_allowed) {
> >> -		drm_dbg_kms(display->drm,
> >> -			    "YCbCr 4:2:0 mode but YCbCr 4:2:0 output not possible. Falling back to RGB.\n");
> >> -		crtc_state->sink_format = INTEL_OUTPUT_FORMAT_RGB;
> >> -	} else {
> >> -		crtc_state->sink_format = intel_dp_sink_format(connector, adjusted_mode);
> >> -	}
> >> +	if (intel_dp_sink_format_valid(connector, adjusted_mode,
> >> +				       sink_format) != MODE_OK)
> >> +		return -EINVAL;
> >>   
> >> +	crtc_state->sink_format = sink_format;
> >>   	crtc_state->output_format = intel_dp_output_format(connector, crtc_state->sink_format);
> >>   
> >> -	ret = intel_dp_compute_link_config(encoder, crtc_state, conn_state,
> >> -					   respect_downstream_limits);
> >> -	if (ret) {
> >> -		if (crtc_state->sink_format == INTEL_OUTPUT_FORMAT_YCBCR420 ||
> >> -		    !connector->base.ycbcr_420_allowed ||
> >> -		    !drm_mode_is_420_also(info, adjusted_mode))
> >> -			return ret;
> >> -
> >> -		crtc_state->sink_format = INTEL_OUTPUT_FORMAT_YCBCR420;
> >> -		crtc_state->output_format = intel_dp_output_format(connector,
> >> -								   crtc_state->sink_format);
> >> -		ret = intel_dp_compute_link_config(encoder, crtc_state, conn_state,
> >> -						   respect_downstream_limits);
> >> +	return intel_dp_compute_link_config(encoder, crtc_state, conn_state,
> >> +					    respect_downstream_limits);
> > With the removal of intel_dp_sink_format in this function, I wonder
> > if we can get rid of it entirely now. It's only called in
> > intel_dp_mode_min_link_bpp_x16, which seems to be used for bandwidth
> > limitation calculations (where YCbCr444 vs RGB444 doesn't matter, so
> > we're fine in that regard).
> 
> I agree we can remove intel_dp_sink_format() but IMO it should be after 
> patch#7 where we are validating sink format for mode valid.
> 
> I guess, with that change, intel_dp_mode_min_link_bpp_x16() can be 
> passed the sink_format directly since we have already validated that.

Aye. I think that really should have been part of patch 5
https://lore.kernel.org/intel-gfx/20260330235339.29479-6-ville.syrjala@linux.intel.com/
where I explicitly pass in the desired sink format.

I'll fix that up.


-- 
Ville Syrjälä
Intel