ddcci-backlight

A Rust Linux kernel module that exposes monitor brightness control through DDC/CI.
It provides a kernel‑space implementation of the DDC/CI protocol, allowing user‑space tools to adjust external monitor brightness using a stable, low‑latency interface.

It lets your desktop environment control your monitor’s built‑in brightness setting, the same one you normally adjust through the monitor’s on‑screen menu, and exposes it as a standard brightness slider in GNOME, KDE, etc.

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Features

Warning

This software is provided without any warranty under GPL‑2.0.
It performs direct DDC/CI communication with monitor firmware, and improper VCP handling, hardware non‑compliance, or unexpected I²C/DDC behavior may result in permanent device damage.
Use with caution and at your own risk.

• Kernel‑space DDC/CI communication
• Rust implementation (no C glue)
• Safe abstractions over I²C/DDC messaging
• Exposes a simple sysfs interface for brightness control
• Nix‑based reproducible build system
• Out‑of‑tree module compatible with modern Linux kernels

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Requirements

• Linux kernel with Rust support enabled
• Kernel headers matching your running kernel
• Nix (optional, but recommended for building)
• A monitor that supports DDC/CI brightness control

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Building (Nix)

To build the kernel module using Nix:

nix build .#ddci-backlight

The resulting module will be located at:

result/lib/modules/<kernel-version>/extra/ddcci_backlight.ko

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Loading the Module

Use it in NixOS

You can consume this module from any external flake by adding it as an input: nix

{
  inputs.ddci-backlight.url = "github:sofiedotcafe/ddci-backlight";
}

{
  boot = {
    kernelPackages = pkgs.linuxPackages_latest;
    extraModulePackages = [
      (pkgs.ddci-backlight.override {
        kernel = config.boot.kernelPackages;
      })
    ];

    kernelModules = [ "ddcci_backlight" ];
  };
}

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Usage

Once loaded, the module exposes a sysfs interface:

/sys/class/backlight/ddcci-backlight/

Common operations:

# Read brightness
cat /sys/class/backlight/ddcci-backlight/brightness

# Set brightness
echo 50 | sudo tee /sys/class/backlight/ddcci-backlight/brightness

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Development

For development, build the project using Nix

nix build .#default

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Code Of Conduct

This project follows the Lix Code of Conduct/Community Standards.

License

This repository is distributed under the GNU General Public License v2 (GPLv2).

GPL-2.0-only © 2026