[SOLVED] xorg/lightdm won't start in a dual gpu setup

aciezk · 2023-10-22 07:48:26

Hi
I've got a dual GPU set-up with configured GPU passtrough to a VM and I've got this problem where xorg/lightdm won't start when a HDMI cable is plugged into my second GPU.
BIOS messages by default seem to be displaying on the second GPU and I can't find how to change it in the settings. My motherboard is MSI B550-A Pro.
When I disable lightdm.service I can access the TTY normally.
My GPUs are 5700xt (primary) and GTX 1060 3GB (secondary).
Which logs should I check for this?

Thanks in advance for help.

Last edited by aciezk (2023-10-23 19:41:36)

seth · 2023-10-22 08:28:30

Please post your Xorg log, https://wiki.archlinux.org/title/Xorg#General

aciezk · 2023-10-22 08:47:02

https://pastebin.com/fMGLkJdS

seth · 2023-10-22 09:24:22

You're trying to pass through the nvidia GPU to the VM, but it's also the primary GPU and the X11 server tries to run on it.
Try to add amdgpu to the initramfs, https://wiki.archlinux.org/title/Kernel … _KMS_start and make sure the nvidia modules aren't in there.

aciezk · 2023-10-22 09:45:27

I've added amdgpu to mkinitcpio.conf and run mkinitcpio.

Now it looks stuck at "Starting systemd-udevd version" on the Nvidia connected screen.
Screen connected to AMD is black but the monitor doesn't go to sleep so looks like the port is sending video.

seth · 2023-10-22 13:30:38

The nvidia GPU probably just keeps reposting the last buffer.

Can you boot the multi-user.target this way (2nd link below)?
Please post an updated xorg log and your complete system journal for the boot:

sudo journalctl -b | curl -F 'file=@-' 0x0.st

aciezk · 2023-10-23 06:53:52

I've tried for the moment swapping the cables and I got it to boot normally with BIOS and everything on second screen connected to the AMD GPU like it should be. Maybe it's a hardware/cable problem or something.

[edit]
Partially solved. I've made Xorg use amdgpu drivers with the xorg.conf,d file and now it boots up to the desktop. Still, BIOS and TTY's display on the wrong monitor. Looks like it was all very simple - the BIOS detects the second screen before my first one and uses it.

[edit2]
After googling I've also set fbcon=map:1 as the kernel parameter and now TTY is on the right screen.

Last edited by aciezk (2023-10-23 19:41:16)

Arch Linux

#1 2023-10-22 07:48:26

[SOLVED] xorg/lightdm won't start in a dual gpu setup

#2 2023-10-22 08:28:30

Re: [SOLVED] xorg/lightdm won't start in a dual gpu setup

#3 2023-10-22 08:47:02

Re: [SOLVED] xorg/lightdm won't start in a dual gpu setup

#4 2023-10-22 09:24:22

Re: [SOLVED] xorg/lightdm won't start in a dual gpu setup

#5 2023-10-22 09:45:27

Re: [SOLVED] xorg/lightdm won't start in a dual gpu setup

#6 2023-10-22 13:30:38

Re: [SOLVED] xorg/lightdm won't start in a dual gpu setup

#7 2023-10-23 06:53:52

Re: [SOLVED] xorg/lightdm won't start in a dual gpu setup

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