Bug 108934 - [Dualscreen] "No signal" issues when booting with DVI and HDMI screens both plugged in
Summary: [Dualscreen] "No signal" issues when booting with DVI and HDMI screens both p...
Status: NEW
Alias: None
Product: DRI
Classification: Unclassified
Component: DRM/AMDgpu (show other bugs)
Version: unspecified
Hardware: x86-64 (AMD64) Linux (All)
: medium normal
Assignee: Default DRI bug account
QA Contact:
Depends on:
Reported: 2018-12-03 20:04 UTC by Laurent Pointecouteau
Modified: 2018-12-08 12:15 UTC (History)
1 user (show)

See Also:
i915 platform:
i915 features:

Boot log with suspend (106.64 KB, text/plain)
2018-12-08 12:15 UTC, Laurent Pointecouteau
no flags Details

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Description Laurent Pointecouteau 2018-12-03 20:04:43 UTC
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.
Comment 1 Michel Dänzer 2018-12-04 10:11:37 UTC
Please attach the corresponding output of dmesg, and the Xorg log file if you're using Xorg.
Comment 2 Laurent Pointecouteau 2018-12-08 12:15:52 UTC
Created attachment 142751 [details]
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.

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