https://bugs.freedesktop.org/show_bug.cgi?id=109246
--- Comment #17 from krutoileshii@gmail.com --- I think this could be related to this commit b0c4e977522c34e20ad54ff4ca104129a7cfdeca which removed the delay.: Below patchset seems to be the likely cause as it touches the HDMI portion.
https://lists.freedesktop.org/archives/amd-gfx/2018-February/018956.html