Comment 0 for bug 1790861

I have a problem with my dual monitor setup on an AMD RX 580: when I lock the screen and Gnome try to power off both monitors the following happens:
1) the second monitor goes to sleep before the first one, this is normal and expected because the first monitor has a longer time to sleep
2) after some seconds the second monitor turn on back again and prevents the first one to sleep at all
3) gnome detects inactivity on the lock screen for some time and try to power off the monitors again
4) step 1 all over again in an infinite loop

When I login back from the lock screen the windows inside my Gnome session can sometimes be rearranged from one screen to the other.

After discovering this behavior I tried to power off the monitors manually with `xset dpms force off` and I can confirm that the same happens: the monitors wont really power off because the second one turns back on and prevents the first one to sleep.

My guess was that somehow when the second monitor was turning off it delivered some kind of "monitors changed, you should reset" message to the GPU which in order did some kind of "reset everything and power on the monitors back again" action.

Searching for a fix to this problem I tried to upgrade my amdgpu mesa drivers using the oibaf/graphics-drivers ppa and after this I tried to upgrade my whole distribution too, moving from bionic to cosmic.

Nothing worked.

In the end I discovered the existence of amdgpu.dc and tried to disable it with `GRUB_CMDLINE_LINUX_DEFAULT="amdgpu.dc=0"`, this did the trick but it is still a workaround.

I'm not sure this is the right place to report this kind of issues but as the issue is somehow critical (the first I entered the power on/off loop I didn't notice it and my monitor cycled power for two hours) I hope this will help other people.