drm/atomic: allow no-op FB_ID updates for async flips

User-space is allowed to submit any property in an async flip as
long as the value doesn't change. However we missed one case:
as things stand, the kernel rejects no-op FB_ID changes on
non-primary planes. Fix this by changing the conditional and
skipping drm_atomic_check_prop_changes() only for FB_ID on the
primary plane (instead of skipping for FB_ID on any plane).

Fixes: 0e26cc72 ("drm: Refuse to async flip with atomic prop changes")
Signed-off-by: Simon Ser <contact@emersion.fr>
Reviewed-by: André Almeida <andrealmeid@igalia.com>
Tested-by: Xaver Hugl <xaver.hugl@kde.org>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Michel Dänzer <michel.daenzer@mailbox.org>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240731191014.878320-1-contact@emersion.fr

drivers/gpu/drm/drm_atomic_uapi.c

@@ -1071,23 +1071,16 @@ int drm_atomic_set_property(struct drm_atomic_state *state,
 		}
 
 		if (async_flip &&
-		    prop != config->prop_fb_id &&
-		    prop != config->prop_in_fence_fd &&
-		    prop != config->prop_fb_damage_clips) {
+		    (plane_state->plane->type != DRM_PLANE_TYPE_PRIMARY ||
+		     (prop != config->prop_fb_id &&
+		      prop != config->prop_in_fence_fd &&
+		      prop != config->prop_fb_damage_clips))) {
 			ret = drm_atomic_plane_get_property(plane, plane_state,
 							    prop, &old_val);
 			ret = drm_atomic_check_prop_changes(ret, old_val, prop_value, prop);
 			break;
 		}
 
-		if (async_flip && plane_state->plane->type != DRM_PLANE_TYPE_PRIMARY) {
-			drm_dbg_atomic(prop->dev,
-				       "[OBJECT:%d] Only primary planes can be changed during async flip\n",
-				       obj->id);
-			ret = -EINVAL;
-			break;
-		}
-
 		ret = drm_atomic_plane_set_property(plane,
 				plane_state, file_priv,
 				prop, prop_value);