drm/virtio: skip set_scanout if framebuffer didn't change

v2: also check src rect (Chia-I Wu).
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Chia-I Wu <olvaffe@gmail.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20191212125346.8334-2-kraxel@redhat.com

drivers/gpu/drm/virtio/virtgpu_plane.c

@@ -151,6 +151,11 @@ static void virtio_gpu_primary_plane_update(struct drm_plane *plane,
 	if (bo->dumb)
 		virtio_gpu_update_dumb_bo(vgdev, bo, plane->state);
 
+	if (plane->state->fb != old_state->fb ||
+	    plane->state->src_w != old_state->src_w ||
+	    plane->state->src_h != old_state->src_h ||
+	    plane->state->src_x != old_state->src_x ||
+	    plane->state->src_y != old_state->src_y) {
 		DRM_DEBUG("handle 0x%x, crtc %dx%d+%d+%d, src %dx%d+%d+%d\n",
 			  bo->hw_res_handle,
 			  plane->state->crtc_w, plane->state->crtc_h,
@@ -165,6 +170,8 @@ static void virtio_gpu_primary_plane_update(struct drm_plane *plane,
 					   plane->state->src_h >> 16,
 					   plane->state->src_x >> 16,
 					   plane->state->src_y >> 16);
+	}
+
 	virtio_gpu_cmd_resource_flush(vgdev, bo->hw_res_handle,
 				      plane->state->src_x >> 16,
 				      plane->state->src_y >> 16,