drm/i915: Add support for limited color range of broadcast outputs

In order to prevent "crushed blacks" on TVs, the range of the RGB output
may be limited to 16-235. This used to be available through Xorg under
the "Broadcast RGB" option, so reintroduce support for KMS.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=34543
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/intel_modes.c

@@ -80,3 +80,33 @@ int intel_ddc_get_modes(struct drm_connector *connector,
 
 	return ret;
 }
+
+static const char *broadcast_rgb_names[] = {
+	"Full",
+	"Limited 16:235",
+};
+
+void
+intel_attach_broadcast_rgb_property(struct drm_connector *connector)
+{
+	struct drm_device *dev = connector->dev;
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	struct drm_property *prop;
+	int i;
+
+	prop = dev_priv->broadcast_rgb_property;
+	if (prop == NULL) {
+		prop = drm_property_create(dev, DRM_MODE_PROP_ENUM,
+					   "Broadcast RGB",
+					   ARRAY_SIZE(broadcast_rgb_names));
+		if (prop == NULL)
+			return;
+
+		for (i = 0; i < ARRAY_SIZE(broadcast_rgb_names); i++)
+			drm_property_add_enum(prop, i, i, broadcast_rgb_names[i]);
+
+		dev_priv->broadcast_rgb_property = prop;
+	}
+
+	drm_connector_attach_property(connector, prop, 0);
+}