Hi Dave,
On Wed, Mar 25, 2026 at 12:49:19PM +0000, Dave Stevenson wrote:
> > diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> > index af8b92d2d5b7..bd549f912b76 100644
> > --- a/include/drm/drm_connector.h
> > +++ b/include/drm/drm_connector.h
> > @@ -571,14 +571,102 @@ enum drm_colorspace {
> > * YCbCr 4:2:2 output format (ie. with horizontal subsampling)
> > * @DRM_OUTPUT_COLOR_FORMAT_YCBCR420:
> > * YCbCr 4:2:0 output format (ie. with horizontal and vertical
> > subsampling)
> > + * @DRM_OUTPUT_COLOR_FORMAT_COUNT:
> > + * Number of valid output color format values in this enum
> > */
> > enum drm_output_color_format {
> > DRM_OUTPUT_COLOR_FORMAT_RGB444 = 0,
> > DRM_OUTPUT_COLOR_FORMAT_YCBCR444,
> > DRM_OUTPUT_COLOR_FORMAT_YCBCR422,
> > DRM_OUTPUT_COLOR_FORMAT_YCBCR420,
> > + DRM_OUTPUT_COLOR_FORMAT_COUNT,
> > };
> >
> > +/**
> > + * enum drm_connector_color_format - Connector Color Format Request
> > + *
> > + * This enum, unlike &enum drm_output_color_format, is used to specify
> > requests
> > + * for a specific color format on a connector through the DRM "color
> > format"
> > + * property. The difference is that it has an "AUTO" value to specify that
> > + * no specific choice has been made.
> > + */
> > +enum drm_connector_color_format {
> > + /**
> > + * @DRM_CONNECTOR_COLOR_FORMAT_AUTO: The driver or display protocol
> > + * helpers should pick a suitable color format. All implementations
> > of a
> > + * specific display protocol must behave the same way with "AUTO",
> > but
> > + * different display protocols do not necessarily have the same
> > "AUTO"
> > + * semantics.
> > + *
> > + * For HDMI, "AUTO" picks RGB, but falls back to YCbCr 4:2:0 if the
> > + * bandwidth required for full-scale RGB is not available, or the
> > mode
> > + * is YCbCr 4:2:0-only, as long as the mode and output both support
> > + * YCbCr 4:2:0.
>
> Is there a reason you propose dropping back to YCbCr 4:2:0 without
> trying YCbCr 4:2:2 first? Minimising the subsampling is surely
> beneficial, and vc4 for one can do 4:2:2 but not 4:2:0.The "auto" behaviour is strictly identical to the one we have right now, and this one stems from i915. Back when all that logic was added, it was decided to align every driver behavior on i915 because that's what most compositors would expect. Maxime
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