[Dualscreen] "No signal" issues when booting with DVI and HDMI screens both plugged in

Submitted by Laurent Pointecouteau

Assigned to Default DRI bug account

Description

I'm using a AMD R9 380 video card on Arch Linux (with kernel 4.19.4 and the latest mesa package installed), and since several weeks, dualscreen has a buggy behavior. My Samsung TV displays "no signal" after booting while plugged in my computer (using a HDMI cable), and when trying to switch display modes using the GNOME control center (or the Super+P shortcut), my Iiyama ProLite B2475HDS DVI monitor gets randomly disabled and displays "no signal" too without ever recovering, forcing me to hard reboot.

I've tried to apply a kernel patch as suggested in bug #108704, but it only removed the amdgpu-related error messages from dmesg, without fixing the dualscreen issues. Since then, I've found two workarounds:

putting the system to sleep then waking it up seems to restore normal functionality;
when booting with the HDMI cable unplugged, after plugging it in, screen switching is not buggy anymore.

My setup does not allow me to safely downgrade to an older kernel, but I can confirm that the screen settings started to exhibit this buggy behaviour only recently.