drm_rect_adjust_size
drm_rect_adjust_size(dst, max_dst_w - dst_w, 0);
drm_rect_adjust_size(src, max_src_w - src_w, 0);
drm_rect_adjust_size(dst, 0, max_dst_h - dst_h);
drm_rect_adjust_size(src, 0, max_src_h - src_h);