drm/panthor: Add PANTHOR_GROUP_PRIORITY_REALTIME group priority

This adds a new value to drm_panthor_group_priority exposing the
realtime priority to userspace.

This is required to implement NV_context_priority_realtime in Mesa.

v2:
- Add Steven Price r-b

v3:
- Add Boris Brezillon r-b

Signed-off-by: Mary Guillemard <mary.guillemard@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Steven Price <steven.price@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240909064820.34982-3-mary.guillemard@collabora.com

drivers/gpu/drm/panthor/panthor_drv.c

@@ -1041,7 +1041,7 @@ static int group_priority_permit(struct drm_file *file,
 				 u8 priority)
 {
 	/* Ensure that priority is valid */
-	if (priority > PANTHOR_GROUP_PRIORITY_HIGH)
+	if (priority > PANTHOR_GROUP_PRIORITY_REALTIME)
 		return -EINVAL;
 
 	/* Medium priority and below are always allowed */

drivers/gpu/drm/panthor/panthor_sched.c

@@ -137,8 +137,6 @@ enum panthor_csg_priority {
 	 * non-real-time groups. When such a group becomes executable,
 	 * it will evict the group with the lowest non-rt priority if
 	 * there's no free group slot available.
-	 *
-	 * Currently not exposed to userspace.
 	 */
 	PANTHOR_CSG_PRIORITY_RT,
 

include/uapi/drm/panthor_drm.h

@@ -720,6 +720,13 @@ enum drm_panthor_group_priority {
 	 * Requires CAP_SYS_NICE or DRM_MASTER.
 	 */
 	PANTHOR_GROUP_PRIORITY_HIGH,
+
+	/**
+	 * @PANTHOR_GROUP_PRIORITY_REALTIME: Realtime priority group.
+	 *
+	 * Requires CAP_SYS_NICE or DRM_MASTER.
+	 */
+	PANTHOR_GROUP_PRIORITY_REALTIME,
 };
 
 /**