https://bugs.freedesktop.org/show_bug.cgi?id=106940
--- Comment #30 from Server Angels seany@seanyseansean.com --- Actually rc8 from fedora/rawhide fixed it for me. I wasn't sure at first as the initial upgrade didn't work, but a full power off / power off then did, which was bizarre.
I did add the kernel option amdgpu.dc=1 to make sure it was using the correct code. All been fine since.