drm/i915: Reject async flips if we need to change DDB/watermarks

DDB/watermarks are always double buffered on the vblank, so we
can't safely change them during async flips. Currently this never
happens, but we'll be making changing between sync and async
flips a bit more flexible, in which case we can actually end up
here.
Reviewed-by: Vandita Kulkarni <vandita.kulkarni@intel.com>
Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240430095639.26390-3-ville.syrjala@linux.intel.com

drivers/gpu/drm/i915/display/skl_watermark.c

@@ -2540,6 +2540,12 @@ skl_ddb_add_affected_planes(const struct intel_crtc_state *old_crtc_state,
 					&new_crtc_state->wm.skl.plane_ddb_y[plane_id]))
 			continue;
 
+		if (new_crtc_state->do_async_flip) {
+			drm_dbg_kms(&i915->drm, "[PLANE:%d:%s] Can't change DDB during async flip\n",
+				    plane->base.base.id, plane->base.name);
+			return -EINVAL;
+		}
+
 		plane_state = intel_atomic_get_plane_state(state, plane);
 		if (IS_ERR(plane_state))
 			return PTR_ERR(plane_state);
@@ -2899,6 +2905,12 @@ static int skl_wm_add_affected_planes(struct intel_atomic_state *state,
 						 &new_crtc_state->wm.skl.optimal))
 			continue;
 
+		if (new_crtc_state->do_async_flip) {
+			drm_dbg_kms(&i915->drm, "[PLANE:%d:%s] Can't change watermarks during async flip\n",
+				    plane->base.base.id, plane->base.name);
+			return -EINVAL;
+		}
+
 		plane_state = intel_atomic_get_plane_state(state, plane);
 		if (IS_ERR(plane_state))
 			return PTR_ERR(plane_state);