On Tue, Mar 24, 2026 at 09:53:35PM +0200, Ville Syrjälä wrote:
> On Tue, Mar 24, 2026 at 08:10:11PM +0100, Nicolas Frattaroli wrote:
> > On Tuesday, 24 March 2026 18:00:45 Central European Standard Time Ville
> > Syrjälä wrote:
> > > On Tue, Mar 24, 2026 at 05:01:07PM +0100, Nicolas Frattaroli wrote:
> > > > +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.
> > > > + *
> > > > + * For display protocols other than HDMI, the recursive bridge
> > > > chain
> > > > + * format selection picks the first chain of bridge formats
> > > > that works,
> > > > + * as has already been the case before the introduction of the
> > > > "color
> > > > + * format" property. Non-HDMI bridges should therefore either
> > > > sort their
> > > > + * bus output formats by preference, or agree on a unified auto
> > > > format
> > > > + * selection logic that's implemented in a common state helper
> > > > (like
> > > > + * how HDMI does it).
> > > > + */
> > > > + DRM_CONNECTOR_COLOR_FORMAT_AUTO = 0,
> > > > +
> > > > + /**
> > > > + * @DRM_CONNECTOR_COLOR_FORMAT_RGB444: RGB output format
> > > > + */
> > > > + DRM_CONNECTOR_COLOR_FORMAT_RGB444,
> > > > +
> > > > + /**
> > > > + * @DRM_CONNECTOR_COLOR_FORMAT_YCBCR444: YCbCr 4:4:4 output
> > > > format (ie.
> > > > + * not subsampled)
> > > > + */
> > > > + DRM_CONNECTOR_COLOR_FORMAT_YCBCR444,
> > > > +
> > > > + /**
> > > > + * @DRM_CONNECTOR_COLOR_FORMAT_YCBCR422: YCbCr 4:2:2 output
> > > > format (ie.
> > > > + * with horizontal subsampling)
> > > > + */
> > > > + DRM_CONNECTOR_COLOR_FORMAT_YCBCR422,
> > > > +
> > > > + /**
> > > > + * @DRM_CONNECTOR_COLOR_FORMAT_YCBCR420: YCbCr 4:2:0 output
> > > > format (ie.
> > > > + * with horizontal and vertical subsampling)
> > > > + */
> > > > + DRM_CONNECTOR_COLOR_FORMAT_YCBCR420,
> > >
> > > Seems like this should document what the quantization range
> > > should be for each format.
> > >
> >
> > I don't think so? If you want per-component bit depth values,
> > DRM_FORMAT_* defines would be the appropriate values to use. This
> > enum is more abstract than that, and is there to communicate
> > YUV vs. RGB and chroma subsampling, with bit depth being handled
> > by other properties.
> >
> > If you mean the factor used for subsampling, then that'd only be
> > relevant if YCBCR410 was supported where one chroma plane isn't
> > halved but quartered in resolution. I suspect 4:1:0 will never
> > be added; no digital display protocol standard supports it to my
> > knowledge, and hopefully none ever will.
>
> No, I mean the quantization range (16-235 vs. 0-255 etc).
>
> The i915 behaviour is that YCbCr is always limited range,
> RGB can either be full or limited range depending on the
> "Broadcast RGB" property and other related factors.So far the HDMI state has both the format and quantization range as different fields. I'm not sure we need to document the range in the format field, maybe only mention it's not part of the format but has a field of its own? Maxime
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