Created attachment 140060 [details]
'xrandr -q' output with and without amdgpu.dc enabled.

Card is an ASUS DUAL-RX480-04G. When booting with amdgpu.dc=1, as is default on
4.17+, the system shows a monitor on both HDMI ports when only one is
connected. This causes a low-resolution login screen and requires disabling the
non-existent monitor to prevent some windows from being opened off screen.

Attached is the 'xrandr -q' output from booting with and without amdgpu.dc
enabled. Behavior is the same regardless of which HDMI port is used.