https://bugzilla.kernel.org/show_bug.cgi?id=200695
--- Comment #31 from Claude Heiland-Allen (claude@mathr.co.uk) --- Created attachment 282101 --> https://bugzilla.kernel.org/attachment.cgi?id=282101&action=edit dmesg logs after booting to X with displays connected to both DVI and HDMI
Good news: the bug only seems to affect the DVI output from my card.
I managed to connect another screen via an HDMI port and it works ok with amdgpu=1 (both screens have kernel messages mirrored until about 5 seconds into boot, when the DVI screen turns off - the HDMI screen stays on and I can log into X).
Attached are 7 dmesg logs, with amdgpu=1 unless specified.