On Tue, 24 Mar 2026 at 16:02, Nicolas Frattaroli
<[email protected]> wrote:
>
> Add a new general DRM property named "color format" which can be used by
> userspace to request the display driver to output a particular color
> format.
>
> Possible options are:
> - auto (setup by default, driver internally picks the color format)
> - rgb
> - ycbcr444
> - ycbcr422
> - ycbcr420
>
> Drivers should advertise from this list which formats they support.
> Together with this list and EDID data from the sink we should be able
> to relay a list of usable color formats to users to pick from.
>
> Co-developed-by: Werner Sembach <[email protected]>
> Signed-off-by: Werner Sembach <[email protected]>
> Co-developed-by: Andri Yngvason <[email protected]>
> Signed-off-by: Andri Yngvason <[email protected]>
> Signed-off-by: Marius Vlad <[email protected]>
> Reviewed-by: Maxime Ripard <[email protected]>
> Signed-off-by: Nicolas Frattaroli <[email protected]>
> ---
> drivers/gpu/drm/drm_atomic_helper.c | 5 ++
> drivers/gpu/drm/drm_atomic_uapi.c | 11 ++++
> drivers/gpu/drm/drm_connector.c | 108
> ++++++++++++++++++++++++++++++++++++
> include/drm/drm_connector.h | 104 ++++++++++++++++++++++++++++++++++
> 4 files changed, 228 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c
> b/drivers/gpu/drm/drm_atomic_helper.c
> index 26953ed6b53e..b7753454b777 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -737,6 +737,11 @@ drm_atomic_helper_check_modeset(struct drm_device *dev,
> if (old_connector_state->max_requested_bpc !=
> new_connector_state->max_requested_bpc)
> new_crtc_state->connectors_changed = true;
> +
> + if (old_connector_state->color_format !=
> + new_connector_state->color_format)
> + new_crtc_state->connectors_changed = true;
> +
> }
>
> if (funcs->atomic_check)
> diff --git a/drivers/gpu/drm/drm_atomic_uapi.c
> b/drivers/gpu/drm/drm_atomic_uapi.c
> index 5bd5bf6661df..dee510c85e59 100644
> --- a/drivers/gpu/drm/drm_atomic_uapi.c
> +++ b/drivers/gpu/drm/drm_atomic_uapi.c
> @@ -935,6 +935,15 @@ static int drm_atomic_connector_set_property(struct
> drm_connector *connector,
> state->privacy_screen_sw_state = val;
> } else if (property == connector->broadcast_rgb_property) {
> state->hdmi.broadcast_rgb = val;
> + } else if (property == connector->color_format_property) {
> + if (val > INT_MAX || !drm_connector_color_format_valid(val)) {
> + drm_dbg_atomic(connector->dev,
> + "[CONNECTOR:%d:%s] unknown color
> format %llu\n",
> + connector->base.id, connector->name,
> val);
> + return -EINVAL;
> + }
> +
> + state->color_format = val;
> } else if (connector->funcs->atomic_set_property) {
> return connector->funcs->atomic_set_property(connector,
> state, property, val);
> @@ -1020,6 +1029,8 @@ drm_atomic_connector_get_property(struct drm_connector
> *connector,
> *val = state->privacy_screen_sw_state;
> } else if (property == connector->broadcast_rgb_property) {
> *val = state->hdmi.broadcast_rgb;
> + } else if (property == connector->color_format_property) {
> + *val = state->color_format;
> } else if (connector->funcs->atomic_get_property) {
> return connector->funcs->atomic_get_property(connector,
> state, property, val);
> diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> index 47dc53c4a738..e848374dee0b 100644
> --- a/drivers/gpu/drm/drm_connector.c
> +++ b/drivers/gpu/drm/drm_connector.c
> @@ -1388,6 +1388,18 @@ static const u32 hdmi_colorspaces =
> BIT(DRM_MODE_COLORIMETRY_DCI_P3_RGB_D65) |
> BIT(DRM_MODE_COLORIMETRY_DCI_P3_RGB_THEATER);
>
> +static const u32 hdmi_colorformats =
> + BIT(DRM_OUTPUT_COLOR_FORMAT_RGB444) |
> + BIT(DRM_OUTPUT_COLOR_FORMAT_YCBCR444) |
> + BIT(DRM_OUTPUT_COLOR_FORMAT_YCBCR422) |
> + BIT(DRM_OUTPUT_COLOR_FORMAT_YCBCR420);
> +
> +static const u32 dp_colorformats =
> + BIT(DRM_OUTPUT_COLOR_FORMAT_RGB444) |
> + BIT(DRM_OUTPUT_COLOR_FORMAT_YCBCR444) |
> + BIT(DRM_OUTPUT_COLOR_FORMAT_YCBCR422) |
> + BIT(DRM_OUTPUT_COLOR_FORMAT_YCBCR420);
> +
> /*
> * As per DP 1.4a spec, 2.2.5.7.5 VSC SDP Payload for Pixel
> Encoding/Colorimetry
> * Format Table 2-120
> @@ -2940,6 +2952,102 @@ int drm_connector_attach_colorspace_property(struct
> drm_connector *connector)
> }
> EXPORT_SYMBOL(drm_connector_attach_colorspace_property);
>
> +/**
> + * drm_connector_attach_color_format_property - create and attach color
> format property
> + * @connector: connector to create the color format property on
> + * @supported_color_formats: bitmask of bit-shifted &enum
> drm_output_color_format
> + * values the connector supports
> + *
> + * Called by a driver to create a color format property. The property is
> + * attached to the connector automatically on success.
> + *
> + * @supported_color_formats should only include color formats the connector
> + * type can actually support.
> + *
> + * Returns:
> + * 0 on success, negative errno on error
> + */
> +int drm_connector_attach_color_format_property(struct drm_connector
> *connector,
> + unsigned long
> supported_color_formats)
> +{
> + struct drm_device *dev = connector->dev;
> + struct drm_prop_enum_list enum_list[DRM_CONNECTOR_COLOR_FORMAT_COUNT];
> + unsigned int i = 0;
> + unsigned long fmt;
> +
> + if (connector->color_format_property)
> + return 0;
> +
> + if (!supported_color_formats) {
> + drm_err(dev, "No supported color formats provided on
> [CONNECTOR:%d:%s]\n",
> + connector->base.id, connector->name);
> + return -EINVAL;
> + }
> +
> + if (supported_color_formats & ~GENMASK(DRM_OUTPUT_COLOR_FORMAT_COUNT
> - 1, 0)) {
> + drm_err(dev, "Unknown color formats provided on
> [CONNECTOR:%d:%s]\n",
> + connector->base.id, connector->name);
> + return -EINVAL;
> + }
> +
> + switch (connector->connector_type) {
> + case DRM_MODE_CONNECTOR_HDMIA:
> + case DRM_MODE_CONNECTOR_HDMIB:
> + if (supported_color_formats & ~hdmi_colorformats) {
> + drm_err(dev, "Color formats not allowed for HDMI on
> [CONNECTOR:%d:%s]\n",
> + connector->base.id, connector->name);
> + return -EINVAL;
> + }
> + break;
> + case DRM_MODE_CONNECTOR_DisplayPort:
> + case DRM_MODE_CONNECTOR_eDP:
> + if (supported_color_formats & ~dp_colorformats) {
> + drm_err(dev, "Color formats not allowed for DP on
> [CONNECTOR:%d:%s]\n",
> + connector->base.id, connector->name);
> + return -EINVAL;
> + }
> + break;
> + }
> +
> + enum_list[0].name = "AUTO";
> + enum_list[0].type = DRM_CONNECTOR_COLOR_FORMAT_AUTO;
> +
> + for_each_set_bit(fmt, &supported_color_formats,
> DRM_OUTPUT_COLOR_FORMAT_COUNT) {
> + switch (fmt) {
> + case DRM_OUTPUT_COLOR_FORMAT_RGB444:
> + enum_list[++i].type =
> DRM_CONNECTOR_COLOR_FORMAT_RGB444;
> + break;
> + case DRM_OUTPUT_COLOR_FORMAT_YCBCR444:
> + enum_list[++i].type =
> DRM_CONNECTOR_COLOR_FORMAT_YCBCR444;
> + break;
> + case DRM_OUTPUT_COLOR_FORMAT_YCBCR422:
> + enum_list[++i].type =
> DRM_CONNECTOR_COLOR_FORMAT_YCBCR422;
> + break;
> + case DRM_OUTPUT_COLOR_FORMAT_YCBCR420:
> + enum_list[++i].type =
> DRM_CONNECTOR_COLOR_FORMAT_YCBCR420;
> + break;
> + default:
> + drm_warn(dev, "Unknown supported format %ld on
> [CONNECTOR:%d:%s]\n",
> + fmt, connector->base.id, connector->name);
> + continue;
> + }
> + enum_list[i].name =
> drm_hdmi_connector_get_output_format_name(fmt);
> + }
> +
> + connector->color_format_property =
> + drm_property_create_enum(dev, DRM_MODE_PROP_ENUM, "color
> format",
> + enum_list, i + 1);
> +
> + if (!connector->color_format_property)
> + return -ENOMEM;
> +
> + drm_object_attach_property(&connector->base,
> connector->color_format_property,
> + DRM_CONNECTOR_COLOR_FORMAT_AUTO);
> +
> + return 0;
> +}
> +EXPORT_SYMBOL(drm_connector_attach_color_format_property);
> +
> /**
> * drm_connector_atomic_hdr_metadata_equal - checks if the hdr metadata
> changed
> * @old_state: old connector state to compare
> 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.
Dave
> + *
> + * 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,
> +
> + /**
> + * @DRM_CONNECTOR_COLOR_FORMAT_COUNT: Number of valid connector color
> + * format values in this enum
> + */
> + DRM_CONNECTOR_COLOR_FORMAT_COUNT,
> +};
> +
> +/**
> + * drm_connector_color_format_valid - Validate drm_connector_color_format
> value
> + * @fmt: value to check against all values of &enum
> drm_connector_color_format
> + *
> + * Checks whether the passed in value of @fmt is one of the allowable values
> in
> + * &enum drm_connector_color_format.
> + *
> + * Returns: %true if it's a valid value for the enum, %false otherwise.
> + */
> +static inline bool __pure
> +drm_connector_color_format_valid(enum drm_connector_color_format fmt)
> +{
> + switch (fmt) {
> + case DRM_CONNECTOR_COLOR_FORMAT_AUTO:
> + case DRM_CONNECTOR_COLOR_FORMAT_RGB444:
> + case DRM_CONNECTOR_COLOR_FORMAT_YCBCR444:
> + case DRM_CONNECTOR_COLOR_FORMAT_YCBCR422:
> + case DRM_CONNECTOR_COLOR_FORMAT_YCBCR420:
> + return true;
> + default:
> + return false;
> + }
> +}
> +
> const char *
> drm_hdmi_connector_get_output_format_name(enum drm_output_color_format fmt);
>
> @@ -1129,6 +1217,13 @@ struct drm_connector_state {
> */
> enum drm_colorspace colorspace;
>
> + /**
> + * @color_format: State variable for Connector property to request
> + * color format change on Sink. This is most commonly used to switch
> + * between RGB to YUV and vice-versa.
> + */
> + enum drm_connector_color_format color_format;
> +
> /**
> * @writeback_job: Writeback job for writeback connectors
> *
> @@ -2127,6 +2222,12 @@ struct drm_connector {
> */
> struct drm_property *colorspace_property;
>
> + /**
> + * @color_format_property: Connector property to set the suitable
> + * color format supported by the sink.
> + */
> + struct drm_property *color_format_property;
> +
> /**
> * @path_blob_ptr:
> *
> @@ -2610,6 +2711,9 @@ bool drm_connector_has_possible_encoder(struct
> drm_connector *connector,
> struct drm_encoder *encoder);
> const char *drm_get_colorspace_name(enum drm_colorspace colorspace);
>
> +int drm_connector_attach_color_format_property(struct drm_connector
> *connector,
> + unsigned long
> supported_color_formats);
> +
> /**
> * drm_for_each_connector_iter - connector_list iterator macro
> * @connector: &struct drm_connector pointer used as cursor
>
> --
> 2.53.0
>
