powerdevil: build with ddcutil support

[HurricanePootis]

Description of changes

Powerdevil supports changing external monitor brightness via ddcutil, which sends DDC protocol messages over an I2C bus to the external monitor. However, powerdevil needs to be built with ddcutil and needs user access for the i2c bus. Therefore, I added ddcutil to the powerdevil package and enabled i2c along with powerdevil in the plasma module.

Shoutout @getchoo for the help!

Things done

• 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/)
• 24.11 Release Notes (or backporting 23.11 and 24.05 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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Add a 👍 reaction to pull requests you find important.

[K900]

This has been brought up before. DDC/CI is very unreliable, and using it incorrectly can lead to permanently messing up your hardware. It should not be enabled by default.

[HurricanePootis]

If you're talking about previous KDE versions, at least starting with version 6.0, KDE has refined their approach to using libddcutil as explained in [this blog](Starting with Plasma 6.0.4, our DDC/CI code was restructured so that a monitor is only hogged for the short time it takes to change the brightness. ddcutil works again as intended in a Plasma session.) here. Furthermore, distros like Arch have enabled ddcutil as of recent, and everything seems to be fine now.

If not enabled by default, could an module be made for users who want and have tested ddc on their system?

[K900]

No, that's not the issue. The issue is that ddcutil, and DDC/CI in general, provides no way to enumerate devices, and has to blindly poke I2C buses and hope the right thing is on the other end, which can severely confuse other I2C hardware.

[HurricanePootis]

Alright, I appreciate the information. Thanks for taking the time for a response 👍