optimus-manager working well with SDDM

[EmmChriss]

TLDR

optimus-manager works flawlessly with SDDM on AMD/NVIDIA optimus laptop. This should maybe be included in the wiki.

Explanation

On Optimus laptops, it's important to be able to switch active video cards; in my case (AMD + NVIDIA), an external monitor will only work if the proprietary nvidia driver is loaded and in use. As such, I experimented a lot trying to start a graphical session in either battery friendly or NVIDIA mode. optimus-manager did the trick for me on X.

On the wiki, optimus-manager is regarded as public enemy number 1 with regard to multi-monitor setups, but with SDDM, I got it working flawlessy. The trick probably lies in an SDDM config file optimus-manager installs by default on Arch:

[X11]
DisplayCommand=/sbin/prime-offload
DisplayStopCommand=/sbin/prime-switch

My theory is due to there being an X11 config file, Xorg starts even if the selected session is a wayland compositor. Due to this, the optimus-manager hooks run without problems. In my hyprland.conf I have env = WLR_DRM_DEVICES,/dev/dri/card0:/dev/dri/card1, so if /dev/dri/card1 (NVIDIA) is available, Hyprland will use it for an external display; no render offloading is done though. Additionally, in my optimus-manager.conf I have:

[optimus]
switching=none
pci_power_control=yes
pci_remove=yes

What makes this work is temporarily removing the NVIDIA card from the pci bus when switching to integrated mode.

The limitations of this include that optimus-manager is not happy about switching to/being in nvidia mode. The only mode that works well with both internal and external monitor is hybrid.

Also, nvidia kernel modesetting is set up according to Arch wiki.