[Bug 108934] [Dualscreen] "No signal" issues when booting with DVI and HDMI screens both plugged in

[b***@freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=108934

Bug ID: 108934
Summary: [Dualscreen] "No signal" issues when booting with DVI
and HDMI screens both plugged in
Product: DRI
Version: unspecified
Hardware: x86-64 (AMD64)
OS: Linux (All)
Status: NEW
Severity: normal
Priority: medium
Component: DRM/AMDgpu
Assignee: dri-***@lists.freedesktop.org
Reporter: ***@gmail.com

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.

[b***@freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=108934

--- Comment #1 from Michel DÀnzer <***@daenzer.net> ---
Please attach the corresponding output of dmesg, and the Xorg log file if
you're using Xorg.

[b***@freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=108934

--- Comment #2 from Laurent Pointecouteau <***@gmail.com> ---
Created attachment 142751
--> https://bugs.freedesktop.org/attachment.cgi?id=142751&action=edit
Boot log with suspend

Hre is my boot log from my current session. The HDMI cable is plugged in during
boot and the HDMI TV displays "No signal". Around ~12:59, I've switched from
the current "Split-screen" setting to "Single screen" (selecting my HDMI TV)
with gnome-control-center, and the DVI screen went black with a "no signal"
message, whereas the TV displays "Unsupported resolution" for a while, then
goes back to "No signal". I've then pressed the Power button of my computer in
order to suspend it, then pressed the Enter touch of my keyboard in order to
wake it up. The two screens then displayed the correct image according to the
"Split-screen" initial setting. Switching to others settings in
gnome-control-center works fine.