Re: [PATCH v9 04/19] drm/display: hdmi-state-helper: Act on color format DRM property

[Maxime Ripard]

Hi,

On Fri, Feb 27, 2026 at 08:20:09PM +0100, Nicolas Frattaroli wrote:
> With the introduction of the "color format" DRM property, which allows
> userspace to request a specific color format, the HDMI state helper
> should implement this.
> 
> Implement it by translating the requested drm_connector_color_format to
> a drm_output_color_format enum value as per the logic HDMI should use
> for this: Auto is translated to RGB, and a fallback to YUV420 is only
> performed if the original color format was auto.
> 
> Signed-off-by: Nicolas Frattaroli <nicolas.frattar...@collabora.com>
> ---
>  drivers/gpu/drm/display/drm_hdmi_state_helper.c | 28 
> +++++++++++++++++++++++--
>  1 file changed, 26 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/display/drm_hdmi_state_helper.c 
> b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
> index 9f3b696aceeb..31c6d55fa995 100644
> --- a/drivers/gpu/drm/display/drm_hdmi_state_helper.c
> +++ b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
> @@ -669,10 +669,34 @@ hdmi_compute_config(const struct drm_connector 
> *connector,
>       unsigned int max_bpc = clamp_t(unsigned int,
>                                      conn_state->max_bpc,
>                                      8, connector->max_bpc);
> +     enum drm_output_color_format fmt;
>       int ret;
>  
> -     ret = hdmi_compute_format_bpc(connector, conn_state, mode, max_bpc,
> -                                   DRM_OUTPUT_COLOR_FORMAT_RGB444);
> +     switch (conn_state->color_format) {
> +     case DRM_CONNECTOR_COLOR_FORMAT_AUTO:
> +     case DRM_CONNECTOR_COLOR_FORMAT_RGB444:
> +             fmt = DRM_OUTPUT_COLOR_FORMAT_RGB444;
> +             break;
> +     case DRM_CONNECTOR_COLOR_FORMAT_YCBCR444:
> +             fmt = DRM_OUTPUT_COLOR_FORMAT_YCBCR444;
> +             break;
> +     case DRM_CONNECTOR_COLOR_FORMAT_YCBCR422:
> +             fmt = DRM_OUTPUT_COLOR_FORMAT_YCBCR422;
> +             break;
> +     case DRM_CONNECTOR_COLOR_FORMAT_YCBCR420:
> +             fmt = DRM_OUTPUT_COLOR_FORMAT_YCBCR420;
> +             break;
> +     default:
> +             drm_dbg_kms(connector->dev, "HDMI does not support color format 
> '%d'.\n",
> +                         conn_state->color_format);
> +             return -EINVAL;
> +     }
> +
> +     ret = hdmi_compute_format_bpc(connector, conn_state, mode, max_bpc, 
> fmt);
> +
> +     if (conn_state->color_format != DRM_CONNECTOR_COLOR_FORMAT_AUTO)
> +             return ret;
> +

We discussed it before, and it wasn't as trivial as it should have been,
but now, I really feel something like the following would be simpler:

if (conn_state->color_format != DRM_CONNECTOR_COLOR_FORMAT_AUTO) {
        enum drm_output_color_format fmt;

        switch (conn_state->color_format) {
        case DRM_CONNECTOR_COLOR_FORMAT_AUTO:
             drm_warn(connector->dev, "The format shouldn't be auto here"); // 
or any better message
             fallthrough;
        case DRM_CONNECTOR_COLOR_FORMAT_RGB444:
             fmt = DRM_OUTPUT_COLOR_FORMAT_RGB444;
             break;
        ....
        }

        return hdmi_compute_format_bpc(connector, conn_state, mode, max_bpc, 
fmt);
}

ret = hdmi_compute_format_bpc(connector, conn_state, mode, max_bpc,
                              DRM_OUTPUT_COLOR_FORMAT_RGB444);

It makes it much clearer what the two branches are, and we don't have to
test for auto multiple times.

Maxime

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