amdgpu.dc=1 triggers graphic card not recognizing native screen resolution

Submitted by Germano Massullo @germano

Assigned to Default DRI bug account

Link to original bug (#107465)

Description

Videocard: RX480
OS: Fedora 28 KDE
Kernel 4.17.9-200.fc28.x86_64

Sometimes when I poweroff the screen, then after some time I turn on it again, the system cannot recognize native screen resolution, and sets it to a weird one. In Plasma system settings, the monitor name is unknown and the native resolution is missing (1600x1050), other resolutions are available instead.. After playing with some resolutions, suddendly the screen name (ViewSonic etc.) returns back.

MrCooper user in #radeon Freenode chat, suggested me to start the system with amdgpu.dc=0 flag. 24 hours of testing seems to confirm that such flag fixes the problem.

I attach dmesg and xorg.0.log of system experiencing the problem