[PATCH v14 03/28] drm: Add new general DRM property "color format"

Nicolas Frattaroli
2026-04-23T19:05:08Z

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 string values for the new enum property are:
- "AUTO" (setup by default, driver internally picks the color format)
- "RGB"
- "YUV 4:4:4"
- "YUV 4:2:2"
- "YUV 4:2:0"

Drivers should advertise from this list the formats they support in an
optimistic best-case scenario. EDID data from the sink can then be used
in the kernel's atomic check phase to restrict this set of formats, as
well as by userspace to make a correct choice in the first place.

Co-developed-by: Werner Sembach <wse@tuxedocomputers.com>
Signed-off-by: Werner Sembach <wse@tuxedocomputers.com>
Co-developed-by: Andri Yngvason <andri@yngvason.is>
Signed-off-by: Andri Yngvason <andri@yngvason.is>
Signed-off-by: Marius Vlad <marius.vlad@collabora.com>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
---
Documentation/gpu/drm-kms.rst | 6 ++
drivers/gpu/drm/drm_atomic_helper.c | 5 ++
drivers/gpu/drm/drm_atomic_uapi.c | 11 +++
drivers/gpu/drm/drm_connector.c | 155 ++++++++++++++++++++++++++++++++++++
include/drm/drm_connector.h | 108 +++++++++++++++++++++++++
5 files changed, 285 insertions(+)

diff --git a/Documentation/gpu/drm-kms.rst b/Documentation/gpu/drm-kms.rst
index 2292e65f044c..da5133b672d3 100644
--- a/Documentation/gpu/drm-kms.rst
+++ b/Documentation/gpu/drm-kms.rst
@@ -599,6 +599,12 @@ Color Management Properties
.. kernel-doc:: drivers/gpu/drm/drm_color_mgmt.c
:doc: overview

+Color Format Property
+---------------------
+
+.. kernel-doc:: drivers/gpu/drm/drm_connector.c
+ :doc: Color format
+
Tile Group Property
-------------------

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index a768398a1884..446857a4945d 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 3fa4d2082cd7..a0fca522f18f 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
@@ -2935,6 +2947,149 @@ int drm_connector_attach_colorspace_property(struct drm_connector *connector)
}
EXPORT_SYMBOL(drm_connector_attach_colorspace_property);

+/**
+ * DOC: Color format
+ *
+ * The connector "color format" property allows userspace to request a specific
+ * color model on the output of the connector. Not all values listed by the
+ * property are guaranteed to work for every sink; rather, it is an optimistic
+ * listing of color formats that the source could output depending on
+ * circumstances.
+ *
+ * Whether it actually can output a certain color format is determined during
+ * the atomic check phase. Consequently, a userspace application that sets the
+ * color format to a value other than "AUTO" should check whether its atomic
+ * commit succeeded.
+ *
+ * Possible values for "color format":
+ *
+ * "AUTO":
+ * The driver or display protocol helpers should pick a suitable color
+ * format. All implementations of a specific display protocol will behave
+ * the same way with "AUTO", but different display protocols do not
+ * necessarily have the same "AUTO" semantics.
+ *
+ * For HDMI connectors, "AUTO" picks RGB, but falls back to YUV 4:2:0 if
+ * the bandwidth required for full-scale RGB is not available, or the mode
+ * is YUV 4:2:0-only, as long as the mode, source, and sink all support
+ * YUV 4:2:0.
+ * "RGB":
+ * RGB output format. The quantization range (limited/full) depends on the
+ * value of the "Broadcast RGB" property if it is present on the connector.
+ * "YUV 4:4:4":
+ * YUV 4:4:4 (a.k.a. YCbCr 4:4:4) output format. Chroma is not subsampled.
+ * The quantization range defaults to limited.
+ * "YUV 4:2:2":
+ * YUV 4:2:2 (a.k.a. YCbCr 4:2:2) output format. Chroma has half the
+ * horizontal resolution of Luma. The quantization range defaults to
+ * limited.
+ * "YUV 4:2:0":
+ * YUV 4:2:0 (a.k.a. YCbCr 4:2:0) output format. Chroma has half the
+ * horizontal and vertical resolution of Luma. The quantization range
+ * defaults to limited.
+ *
+ * A sink may only support some color formats in specific modes and at specific
+ * bit depths. The atomic modesetting API should be used to set a working
+ * configuration in one go, as an unsupported combination of parameters is
+ * rejected.
+ */
+
+/**
+ * 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 3e422a4f2e72..3f7b94e4d83d 100644
--- a/include/drm/drm_connector.h
+++ b/include/drm/drm_connector.h
@@ -571,14 +571,106 @@ 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.
+ *
+ * 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. The
+ * quantization range depends on the value of the "Broadcast RGB"
+ * property if it is present on the connector.
+ */
+ DRM_CONNECTOR_COLOR_FORMAT_RGB444,
+
+ /**
+ * @DRM_CONNECTOR_COLOR_FORMAT_YCBCR444: YCbCr 4:4:4 output format (ie.
+ * not subsampled). Quantization range is "Limited" by default.
+ */
+ DRM_CONNECTOR_COLOR_FORMAT_YCBCR444,
+
+ /**
+ * @DRM_CONNECTOR_COLOR_FORMAT_YCBCR422: YCbCr 4:2:2 output format (ie.
+ * with horizontal subsampling). Quantization range is "Limited" by
+ * default.
+ */
+ DRM_CONNECTOR_COLOR_FORMAT_YCBCR422,
+
+ /**
+ * @DRM_CONNECTOR_COLOR_FORMAT_YCBCR420: YCbCr 4:2:0 output format (ie.
+ * with horizontal and vertical subsampling). Quantization range is
+ * "Limited" by default.
+ */
+ 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);

@@ -1167,6 +1259,13 @@ 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
*
@@ -2165,6 +2264,12 @@ 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:
*
@@ -2648,6 +2753,9 @@ 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