[PATCH] drm: document userspace expectations around the Colorspace connector property

[Pekka Paalanen]

On Fri,  9 Feb 2024 17:53:07 +0100
Xaver Hugl <xaver.hugl at kde.org> wrote:

> Signed-off-by: Xaver Hugl <xaver.hugl at kde.org>
> ---
>  drivers/gpu/drm/drm_connector.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> index b0516505f7ae..01e13984629b 100644
> --- a/drivers/gpu/drm/drm_connector.c
> +++ b/drivers/gpu/drm/drm_connector.c
> @@ -2158,6 +2158,14 @@ EXPORT_SYMBOL(drm_mode_create_aspect_ratio_property);
>   *     one supported. Sink supported colorspaces should be retrieved by
>   *     userspace from EDID and driver will not explicitly expose them.
>   *
> + *     As userspace can't currently know whether or not the output is using
> + *     RGB or YCC signalling, the driver must translate properties to their
> + *     relevant RGB or YCC counterparts, depending on the actually used
> + *     signalling. Property values that are only valid for either YCC or RGB
> + *     and have no equivalent for the other signalling type must not be
> + *     exposed as supported, unless the driver can guarantee it never uses
> + *     the signalling that doesn't match the property.
> + *
>   *     Basically the expectation from userspace is:
>   *      - Set up CRTC DEGAMMA/CTM/GAMMA to convert to some sink
>   *        colorspace

While this addition is good, I have another question:

Does "Colorspace" property choose also the RGB->YCbCr matrix that the
driver will use when it happens to use YCbCr signalling?

So far we have only been talking about the primaries and white point.
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