Comment # 5 on bug 108139 from Alex Deucher

(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.