I have a weird problem while switching vts
I have a dual-GPU setup: intel i5-5200U as the default OpenGL renderer and GeForce 940M as the discrete card. I'm using the intel modesetting driver for the Intel graphics and xf86-video-nouveau for DRI_PRIME.
If I run SDDM/LXDM as my display manager (on Arch Linux), then switch the TTY to tty2, then switch back to tty7 (DM), I get only a blinking cursor.
If I run LightDM as my display manager, it survives a tty switch, but if I start an X server in tty2 and then switch directly to tty7, LightDM crashes.
If I switch tty2 -> tty3 (no x server) -> tty7, on the other hand, the DM does *not* crash.
The whole problem doesn't occur when using the `nomodeset` kernel option, (i.e. when my DE runs in software rendering mode)
Whenever I switch the ttys or when I launch the DM I get the following output in the dmesg log: https://pastebin.com/FgzZLEGg
I asked about it on #nouveau and I was told that since the intel driver takes care of the rendering, it is the one to blame here.
On the intel side, the problem occurs with both xf86-video-intel and the modesetting driver
The problem only occurs with the X server that is launched by a DM. If I run startx directly from the tty on both vts, everything works correctly.
It is not observed on a machine without nvidia graphics and with intel i5-7500K as the CPU/integrated GPU, with fairly same software stack.
OS: Arch Linux, DE: Cinnamon
Try booting with nouveau.modeset=0 to rule out any nouveau interaction in your problem.
But perhaps the issue lies in the fact that nouveau suspends the GPU and intel is waiting on some fence to complete?
With nouveau.modeset=0 I get a black screen in the tty the DM is running in. Attaching the journal and dmesg.
Created attachment 133717 [details]
dmesg with nouveau.modeset=0
Created attachment 133718 [details]
journal with nouveau.modeset=0
As for suspending the Nvidia GPU - I ran
inside my DM manager to make sure that the Nvidia GPU remains powered on. The problem persists even then.
Freedesktop's Bugzilla instance is EOLed and open bugs are about to be migrated to http://gitlab.freedesktop.org.
To avoid migrating out of date bugs, I am now closing all the bugs that did not see any activity in the past year. If the issue is still happening, please create a new bug in the relevant project at https://gitlab.freedesktop.org/drm (use misc by default).
Sorry about the noise!