drm: Add vrr_capable property to the drm connector

Modern display hardware is capable of supporting variable refresh rates.
This patch introduces the "vrr_capable" property on the connector to
allow userspace to query support for variable refresh rates.

Atomic drivers should attach this property to connectors that are
capable of driving variable refresh rates using
drm_connector_attach_vrr_capable_property().

The value should be updated based on driver and hardware capability
by using drm_connector_set_vrr_capable_property().
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/drm_connector.c

@@ -1271,6 +1271,37 @@ int drm_mode_create_scaling_mode_property(struct drm_device *dev)
 }
 EXPORT_SYMBOL(drm_mode_create_scaling_mode_property);
 
+/**
+ * drm_connector_attach_vrr_capable_property - creates the
+ * vrr_capable property
+ * @connector: connector to create the vrr_capable property on.
+ *
+ * This is used by atomic drivers to add support for querying
+ * variable refresh rate capability for a connector.
+ *
+ * Returns:
+ * Zero on success, negative errono on failure.
+ */
+int drm_connector_attach_vrr_capable_property(
+	struct drm_connector *connector)
+{
+	struct drm_device *dev = connector->dev;
+	struct drm_property *prop;
+
+	if (!connector->vrr_capable_property) {
+		prop = drm_property_create_bool(dev, DRM_MODE_PROP_IMMUTABLE,
+			"vrr_capable");
+		if (!prop)
+			return -ENOMEM;
+
+		connector->vrr_capable_property = prop;
+		drm_object_attach_property(&connector->base, prop, 0);
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_connector_attach_vrr_capable_property);
+
 /**
  * drm_connector_attach_scaling_mode_property - attach atomic scaling mode property
  * @connector: connector to attach scaling mode property on.
@@ -1599,6 +1630,24 @@ void drm_connector_set_link_status_property(struct drm_connector *connector,
 }
 EXPORT_SYMBOL(drm_connector_set_link_status_property);
 
+/**
+ * drm_connector_set_vrr_capable_property - sets the variable refresh rate
+ * capable property for a connector
+ * @connector: drm connector
+ * @capable: True if the connector is variable refresh rate capable
+ *
+ * Should be used by atomic drivers to update the indicated support for
+ * variable refresh rate over a connector.
+ */
+void drm_connector_set_vrr_capable_property(
+		struct drm_connector *connector, bool capable)
+{
+	drm_object_property_set_value(&connector->base,
+				      connector->vrr_capable_property,
+				      capable);
+}
+EXPORT_SYMBOL(drm_connector_set_vrr_capable_property);
+
 /**
  * drm_connector_init_panel_orientation_property -
  *	initialize the connecters panel_orientation property

include/drm/drm_connector.h

@@ -959,6 +959,17 @@ struct drm_connector {
 	 */
 	struct drm_property *scaling_mode_property;
 
+	/**
+	 * @vrr_capable_property: Optional property to help userspace
+	 * query hardware support for variable refresh rate on a connector.
+	 * connector. Drivers can add the property to a connector by
+	 * calling drm_connector_attach_vrr_capable_property().
+	 *
+	 * This should be updated only by calling
+	 * drm_connector_set_vrr_capable_property().
+	 */
+	struct drm_property *vrr_capable_property;
+
 	/**
 	 * @content_protection_property: DRM ENUM property for content
 	 * protection. See drm_connector_attach_content_protection_property().
@@ -1251,6 +1262,8 @@ int drm_mode_create_scaling_mode_property(struct drm_device *dev);
 int drm_connector_attach_content_type_property(struct drm_connector *dev);
 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_content_protection_property(
 		struct drm_connector *connector);
 int drm_mode_create_aspect_ratio_property(struct drm_device *dev);
@@ -1267,6 +1280,8 @@ int drm_connector_update_edid_property(struct drm_connector *connector,
 				       const struct edid *edid);
 void drm_connector_set_link_status_property(struct drm_connector *connector,
 					    uint64_t link_status);
+void drm_connector_set_vrr_capable_property(
+		struct drm_connector *connector, bool capable);
 int drm_connector_init_panel_orientation_property(
 	struct drm_connector *connector, int width, int height);