https://bugs.freedesktop.org/show_bug.cgi?id=108139
--- Comment #5 from Alex Deucher alexdeucher@gmail.com --- (In reply to Nicholas Kazlauskas from comment #2)
Do you mind posting a full dmesg log for your 4.18 kernel? It would probably help to have drm.debug=4 in your boot parameters as well for this.
Is deep color support on Stoney limited? IIRC, there were some limitations.