[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.frattaroli at 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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