drm/virtio: add plane check

Use drm_atomic_helper_check_plane_state()
to sanity check the plane state.
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Chia-I Wu <olvaffe@gmail.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20190822094657.27483-1-kraxel@redhat.com

drivers/gpu/drm/virtio/virtgpu_plane.c

@@ -84,7 +84,22 @@ static const struct drm_plane_funcs virtio_gpu_plane_funcs = {
 static int virtio_gpu_plane_atomic_check(struct drm_plane *plane,
 					 struct drm_plane_state *state)
 {
-	return 0;
+	bool is_cursor = plane->type == DRM_PLANE_TYPE_CURSOR;
+	struct drm_crtc_state *crtc_state;
+	int ret;
+
+	if (!state->fb || !state->crtc)
+		return 0;
+
+	crtc_state = drm_atomic_get_crtc_state(state->state, state->crtc);
+	if (IS_ERR(crtc_state))
+                return PTR_ERR(crtc_state);
+
+	ret = drm_atomic_helper_check_plane_state(state, crtc_state,
+						  DRM_PLANE_HELPER_NO_SCALING,
+						  DRM_PLANE_HELPER_NO_SCALING,
+						  is_cursor, true);
+	return ret;
 }
 
 static void virtio_gpu_primary_plane_update(struct drm_plane *plane,