Blank screen after locking and vt-switch

Submitted by Yves-Alexis

Assigned to Intel GFX Bugs mailing list

Link to original bug (#110863)

Description

Hi,

I'm reporting a bug as the Debian maintainer of the Xfce desktop environment. Since people have started to upgrade to future new stable version (Buster, currently testing) I have had multiple bug reports with a similar behavior.

The locking infrastructure in Debian buster with Xfce relies on following components:

• LightDM (the login screen manager) with its greeter, lightdm-gtk-greeter
  
• light-locker: the lock screen
  

light-locker works by drawing a simple window on top of the desktop on VT7 and locking it, then doing a vt-switch to a new lightdm on VT8. When entering the correct login/password on the login screen, a DBus message is sent to light-locker which unlocks the screen.

Unfortunately, on setups with Intel adapters (of various generations, I personnaly reproduced on a ThinkPad X250 with Broadwell and Thinkpad X230 with Ivy Bridge) when the screen is then shut down (for power saving or because of a suspend), the screen doesn't turn back on when moving the mouse or entering keys.

As far as I can tell the only way to bring back the screen is to manually switch VT (with ctrl-alt-Fx).

There's a downtream bug report at https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=805711 but unfortunately there's a lot of noise so I'm a bit lost myself.

There's an upstream bug report on Light Locker (https://github.com/the-cavalry/light-locker/issues/108) but it doesn't seem completely related.


uname -m: x86_64 (but I guess i386 is affected as well)
uname -r: 4.19.0-4-amd64
Linux Distribution: Debian testing/sid
Machine: at least ThinkPads X230 and X250 for me but Debian bug report shows a lot more
Display connector: LVDS, eDP, DP (and I guess HDMI, VGA...)
- DDX is modesetting from Xorg core

If you want more specific information please ask. I know the issue is weird. It's likely a bad interaction between various components (i915, DDX) and a not-often used codepath (vt-switch + DPMS maybe?)