Raven machine doesn't start X correctly on agd5f's drm-next branch

I'm seeing lots of this in the logs:

Jun 26 20:43:56 quark kernel: amdgpu 0000:08:00.0: amdgpu: failed to write reg 28b4 wait reg 28c6
Jun 26 20:44:09 quark kernel: amdgpu 0000:08:00.0: amdgpu: failed to write reg 1a6f4 wait reg 1a706

KDE then doesn't load, it clearly starts to but doesn't finish, the machine remains responsive via ssh

Things look fine on 6.4.0, but I'm seeing issues on both @agd5f & @airlied drm-next branches

Dmesg: dmesg.broken

I'll try and bisect now