drm/connector: hdmi: Add Broadcast RGB property

The i915 driver has a property to force the RGB range of an HDMI output.
The vc4 driver then implemented the same property with the same
semantics. KWin has support for it, and a PR for mutter is also there to
support it.

Both drivers implementing the same property with the same semantics,
plus the userspace having support for it, is proof enough that it's
pretty much a de-facto standard now and we can provide helpers for it.

Let's plumb it into the newly created HDMI connector.

Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Reviewed-by: Sebastian Wick <sebastian.wick@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240527-kms-hdmi-connector-state-v15-18-c5af16c3aae2@kernel.org
Signed-off-by: Maxime Ripard <mripard@kernel.org>

Documentation/gpu/kms-properties.csv

@@ -17,7 +17,6 @@ Owner Module/Drivers,Group,Property Name,Type,Property Values,Object attached,De
 ,Virtual GPU,“suggested X”,RANGE,"Min=0, Max=0xffffffff",Connector,property to suggest an X offset for a connector
 ,,“suggested Y”,RANGE,"Min=0, Max=0xffffffff",Connector,property to suggest an Y offset for a connector
 ,Optional,"""aspect ratio""",ENUM,"{ ""None"", ""4:3"", ""16:9"" }",Connector,TDB
-i915,Generic,"""Broadcast RGB""",ENUM,"{ ""Automatic"", ""Full"", ""Limited 16:235"" }",Connector,"When this property is set to Limited 16:235 and CTM is set, the hardware will be programmed with the result of the multiplication of CTM by the limited range matrix to ensure the pixels normally in the range 0..1.0 are remapped to the range 16/255..235/255."
 ,,“audio”,ENUM,"{ ""force-dvi"", ""off"", ""auto"", ""on"" }",Connector,TBD
 ,SDVO-TV,“mode”,ENUM,"{ ""NTSC_M"", ""NTSC_J"", ""NTSC_443"", ""PAL_B"" } etc.",Connector,TBD
 ,,"""left_margin""",RANGE,"Min=0, Max= SDVO dependent",Connector,TBD

drivers/gpu/drm/display/drm_hdmi_state_helper.c

@@ -25,6 +25,7 @@ void __drm_atomic_helper_connector_hdmi_reset(struct drm_connector *connector,
 
 	new_conn_state->max_bpc = max_bpc;
 	new_conn_state->max_requested_bpc = max_bpc;
+	new_conn_state->hdmi.broadcast_rgb = DRM_HDMI_BROADCAST_RGB_AUTO;
 }
 EXPORT_SYMBOL(__drm_atomic_helper_connector_hdmi_reset);
 
@@ -332,7 +333,8 @@ int drm_atomic_helper_connector_hdmi_check(struct drm_connector *connector,
 	if (ret)
 		return ret;
 
-	if (old_conn_state->hdmi.output_bpc != new_conn_state->hdmi.output_bpc ||
+	if (old_conn_state->hdmi.broadcast_rgb != new_conn_state->hdmi.broadcast_rgb ||
+	    old_conn_state->hdmi.output_bpc != new_conn_state->hdmi.output_bpc ||
 	    old_conn_state->hdmi.output_format != new_conn_state->hdmi.output_format) {
 		struct drm_crtc *crtc = new_conn_state->crtc;
 		struct drm_crtc_state *crtc_state;

drivers/gpu/drm/drm_atomic.c

@@ -1145,6 +1145,8 @@ static void drm_atomic_connector_print_state(struct drm_printer *p,
 
 	if (connector->connector_type == DRM_MODE_CONNECTOR_HDMIA ||
 	    connector->connector_type == DRM_MODE_CONNECTOR_HDMIB) {
+		drm_printf(p, "\tbroadcast_rgb=%s\n",
+			   drm_hdmi_connector_get_broadcast_rgb_name(state->hdmi.broadcast_rgb));
 		drm_printf(p, "\toutput_bpc=%u\n", state->hdmi.output_bpc);
 		drm_printf(p, "\toutput_format=%s\n",
 			   drm_hdmi_connector_get_output_format_name(state->hdmi.output_format));

drivers/gpu/drm/drm_atomic_uapi.c

@@ -776,6 +776,8 @@ static int drm_atomic_connector_set_property(struct drm_connector *connector,
 		state->max_requested_bpc = val;
 	} else if (property == connector->privacy_screen_sw_state_property) {
 		state->privacy_screen_sw_state = val;
+	} else if (property == connector->broadcast_rgb_property) {
+		state->hdmi.broadcast_rgb = val;
 	} else if (connector->funcs->atomic_set_property) {
 		return connector->funcs->atomic_set_property(connector,
 				state, property, val);
@@ -859,6 +861,8 @@ drm_atomic_connector_get_property(struct drm_connector *connector,
 		*val = state->max_requested_bpc;
 	} else if (property == connector->privacy_screen_sw_state_property) {
 		*val = state->privacy_screen_sw_state;
+	} else if (property == connector->broadcast_rgb_property) {
+		*val = state->hdmi.broadcast_rgb;
 	} else if (connector->funcs->atomic_get_property) {
 		return connector->funcs->atomic_get_property(connector,
 				state, property, val);

drivers/gpu/drm/drm_connector.c

@@ -1212,6 +1212,29 @@ static const u32 dp_colorspaces =
 	BIT(DRM_MODE_COLORIMETRY_BT2020_CYCC) |
 	BIT(DRM_MODE_COLORIMETRY_BT2020_YCC);
 
+static const struct drm_prop_enum_list broadcast_rgb_names[] = {
+	{ DRM_HDMI_BROADCAST_RGB_AUTO, "Automatic" },
+	{ DRM_HDMI_BROADCAST_RGB_FULL, "Full" },
+	{ DRM_HDMI_BROADCAST_RGB_LIMITED, "Limited 16:235" },
+};
+
+/*
+ * drm_hdmi_connector_get_broadcast_rgb_name - Return a string for HDMI connector RGB broadcast selection
+ * @broadcast_rgb: Broadcast RGB selection to compute name of
+ *
+ * Returns: the name of the Broadcast RGB selection, or NULL if the type
+ * is not valid.
+ */
+const char *
+drm_hdmi_connector_get_broadcast_rgb_name(enum drm_hdmi_broadcast_rgb broadcast_rgb)
+{
+	if (broadcast_rgb >= ARRAY_SIZE(broadcast_rgb_names))
+		return NULL;
+
+	return broadcast_rgb_names[broadcast_rgb].name;
+}
+EXPORT_SYMBOL(drm_hdmi_connector_get_broadcast_rgb_name);
+
 static const char * const output_format_str[] = {
 	[HDMI_COLORSPACE_RGB]		= "RGB",
 	[HDMI_COLORSPACE_YUV420]	= "YUV 4:2:0",
@@ -1708,6 +1731,38 @@ EXPORT_SYMBOL(drm_connector_attach_dp_subconnector_property);
 /**
  * DOC: HDMI connector properties
  *
+ * Broadcast RGB (HDMI specific)
+ *      Indicates the Quantization Range (Full vs Limited) used. The color
+ *      processing pipeline will be adjusted to match the value of the
+ *      property, and the Infoframes will be generated and sent accordingly.
+ *
+ *      This property is only relevant if the HDMI output format is RGB. If
+ *      it's one of the YCbCr variant, it will be ignored.
+ *
+ *      The CRTC attached to the connector must be configured by user-space to
+ *      always produce full-range pixels.
+ *
+ *      The value of this property can be one of the following:
+ *
+ *      Automatic:
+ *              The quantization range is selected automatically based on the
+ *              mode according to the HDMI specifications (HDMI 1.4b - Section
+ *              6.6 - Video Quantization Ranges).
+ *
+ *      Full:
+ *              Full quantization range is forced.
+ *
+ *      Limited 16:235:
+ *              Limited quantization range is forced. Unlike the name suggests,
+ *              this works for any number of bits-per-component.
+ *
+ *      Property values other than Automatic can result in colors being off (if
+ *      limited is selected but the display expects full), or a black screen
+ *      (if full is selected but the display expects limited).
+ *
+ *      Drivers can set up this property by calling
+ *      drm_connector_attach_broadcast_rgb_property().
+ *
  * content type (HDMI specific):
  *	Indicates content type setting to be used in HDMI infoframes to indicate
  *	content type for the external device, so that it adjusts its display
@@ -2570,6 +2625,39 @@ int drm_connector_attach_hdr_output_metadata_property(struct drm_connector *conn
 }
 EXPORT_SYMBOL(drm_connector_attach_hdr_output_metadata_property);
 
+/**
+ * drm_connector_attach_broadcast_rgb_property - attach "Broadcast RGB" property
+ * @connector: connector to attach the property on.
+ *
+ * This is used to add support for forcing the RGB range on a connector
+ *
+ * Returns:
+ * Zero on success, negative errno on failure.
+ */
+int drm_connector_attach_broadcast_rgb_property(struct drm_connector *connector)
+{
+	struct drm_device *dev = connector->dev;
+	struct drm_property *prop;
+
+	prop = connector->broadcast_rgb_property;
+	if (!prop) {
+		prop = drm_property_create_enum(dev, DRM_MODE_PROP_ENUM,
+						"Broadcast RGB",
+						broadcast_rgb_names,
+						ARRAY_SIZE(broadcast_rgb_names));
+		if (!prop)
+			return -EINVAL;
+
+		connector->broadcast_rgb_property = prop;
+	}
+
+	drm_object_attach_property(&connector->base, prop,
+				   DRM_HDMI_BROADCAST_RGB_AUTO);
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_connector_attach_broadcast_rgb_property);
+
 /**
  * drm_connector_attach_colorspace_property - attach "Colorspace" property
  * @connector: connector to attach the property on.

include/drm/drm_connector.h

@@ -369,6 +369,29 @@ enum drm_panel_orientation {
 	DRM_MODE_PANEL_ORIENTATION_RIGHT_UP,
 };
 
+/**
+ * enum drm_hdmi_broadcast_rgb - Broadcast RGB Selection for an HDMI @drm_connector
+ */
+enum drm_hdmi_broadcast_rgb {
+	/**
+	 * @DRM_HDMI_BROADCAST_RGB_AUTO: The RGB range is selected
+	 * automatically based on the mode.
+	 */
+	DRM_HDMI_BROADCAST_RGB_AUTO,
+
+	/**
+	 * @DRM_HDMI_BROADCAST_RGB_FULL: Full range RGB is forced.
+	 */
+	DRM_HDMI_BROADCAST_RGB_FULL,
+
+	/**
+	 * @DRM_HDMI_BROADCAST_RGB_LIMITED: Limited range RGB is forced.
+	 */
+	DRM_HDMI_BROADCAST_RGB_LIMITED,
+};
+
+const char *
+drm_hdmi_connector_get_broadcast_rgb_name(enum drm_hdmi_broadcast_rgb broadcast_rgb);
 const char *
 drm_hdmi_connector_get_output_format_name(enum hdmi_colorspace fmt);
 
@@ -1041,6 +1064,12 @@ struct drm_connector_state {
 	 * @drm_atomic_helper_connector_hdmi_check().
 	 */
 	struct {
+		/**
+		 * @broadcast_rgb: Connector property to pass the
+		 * Broadcast RGB selection value.
+		 */
+		enum drm_hdmi_broadcast_rgb broadcast_rgb;
+
 		/**
 		 * @output_bpc: Bits per color channel to output.
 		 */
@@ -1757,6 +1786,12 @@ struct drm_connector {
 	 */
 	struct drm_property *privacy_screen_hw_state_property;
 
+	/**
+	 * @broadcast_rgb_property: Connector property to set the
+	 * Broadcast RGB selection to output with.
+	 */
+	struct drm_property *broadcast_rgb_property;
+
 #define DRM_CONNECTOR_POLL_HPD (1 << 0)
 #define DRM_CONNECTOR_POLL_CONNECT (1 << 1)
 #define DRM_CONNECTOR_POLL_DISCONNECT (1 << 2)
@@ -2096,6 +2131,7 @@ int drm_connector_attach_scaling_mode_property(struct drm_connector *connector,
 					       u32 scaling_mode_mask);
 int drm_connector_attach_vrr_capable_property(
 		struct drm_connector *connector);
+int drm_connector_attach_broadcast_rgb_property(struct drm_connector *connector);
 int drm_connector_attach_colorspace_property(struct drm_connector *connector);
 int drm_connector_attach_hdr_output_metadata_property(struct drm_connector *connector);
 bool drm_connector_atomic_hdr_metadata_equal(struct drm_connector_state *old_state,