fix kmscon module

[hustlerone]

Things done

Adjusted the systemd unit for kmscon to fix #385497

This however will completely disable DRM for kmscon and now seats will be unspecified.
If someone absolutely requires DRM for kmscon, let me know.

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 25.05 Release Notes (or backporting 24.11 and 25.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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[hustlerone]

As per fbcon fashion, there's rendering issues. I guess the PR will get much more complicated if this doesn't turn out to be a fluke.

[hustlerone]

Ok, this might just be a greetd issue I'm having.

Either way, it would be great if someone would test this under "normal" circumstances

[liff]

Enabled with GNOME and it seems to work like it used to. Didn’t test extensively, but at least GDM is able to start now.

[hustlerone]

Yeah, I suspect the current rev we're in actually works as intended and we actually have to disable DRM specifically.

There also is the option to patch kmscon to allow it to free the gpu on demand. However, we would also have to modify every single derivation that starts a graphical session or needs /dev/dri/cardX so it also tells kmscon to free the GPU, just so we use DRM for kmscon (and I don't know any benefits of using DRM over fbcon for kmscon)

[hustlerone]

how do i undo this git has played me

[nixos-discourse]

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/prs-ready-for-review/3032/5352

[andrewathalye]

Graphical sessions do launch, but I’ve noticed both PipeWire and 3D acceleration don’t seem to work properly. PipeWire only shows the dummy output, even though the service is running and WirePlumber works, 3D acceleration works in X11 but not Wayland apps.

[andrewathalye]

This is the same whether I use DRM or no-drm, hwaccel or no-hwaccel in configuration

[hustlerone]

hwaccel is supposed to be for drawing kmscon only.

If you run under kmscon, you have to wrap your graphical sessions with kmscon-launch-gui like so:

kmscon-launch-gui sway

[andrewathalye]

libEGL warning: pci id for fd 24: 10de:1e84, driver (null)

pci id for fd 51: 10de:1e84, driver (null)
pci id for fd 64: 10de:1e84, driver (null)
libEGL warning: egl: failed to create dri2 screen
pci id for fd 64: 10de:1e84, driver (null)
pci id for fd 69: 10de:1e84, driver (null)
libEGL warning: egl: failed to create dri2 screen

I get these kinds of errors when launching e.g. Anki or Firefox and using Wayland. When using X11, video acceleration works, and the compositor itself seems to have GPU access, but only when I use seatd. If I try to use logind instead it doesn’t launch.

This is something to do with the way Nix is launching kmscon I think

[hustlerone]

Also could be seat-related. Kmscon is starting to get a much needed facelift

[gaelj]

Please rebase this on latest master, I'd love to see it merged

[ccicnce113424]

Pressing the Backspace key did not move the cursor backward. Furthermore, the following error appeared after logging in:

/nix/store/qm7yzix9jc0bwmBkOvw5Bbbnad99kiyl-set-environment:36: can't find terminal definition for $TERM
/nix/store/qm7yzix9jc0bwmBkOvw5Bbbnad99kiyl-set-environment:56: can't find terminal definition for $TERM

[hustlerone]

That's strange considering i copied the service verbatim.

I don't have the issue on agetty. What's your setup?

[ccicnce113424]

Pressing the Backspace key did not move the cursor backward. Furthermore, the following error appeared after logging in:

/nix/store/qm7yzix9jc0bwmBkOvw5Bbbnad99kiyl-set-environment:36: can't find terminal definition for $TERM
/nix/store/qm7yzix9jc0bwmBkOvw5Bbbnad99kiyl-set-environment:56: can't find terminal definition for $TERM

This seems to occur only when the user's default shell is zsh.
users.defaultUserShell = pkgs.zsh;

[gaelj]

I'm using zsh too and it's working well for me when the VT is opened first time, which covers 90% of my use. But if I open another VT and then I go back into an already open VT:

• screen stays black until I press a key (always)
• Ctrl key appears to be "stuck" (always pressed) but this happens on random. I haven't found a way to unstick it once the VT is in this mode

However both problems still exist when I don't use this PR, so it looks like an upstream issue.

[ccicnce113424]

Pressing the Backspace key did not move the cursor backward. Furthermore, the following error appeared after logging in:

/nix/store/qm7yzix9jc0bwmBkOvw5Bbbnad99kiyl-set-environment:36: can't find terminal definition for $TERM
/nix/store/qm7yzix9jc0bwmBkOvw5Bbbnad99kiyl-set-environment:56: can't find terminal definition for $TERM

After applying #483176, it no longer occurs.