Backlight - Revision history

Natejank: remove extraneous spaces

2026-01-26T17:56:54Z

remove extraneous spaces

← Older revision		Revision as of 17:56, 26 January 2026
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	You can then bind this to a hotkey or similar.		You can then bind this to a hotkey or similar.



	To make this permanent, add {{nixos:package\|ddcutil}} to your system packages, and enable i2c support.<syntaxhighlight lang="nix">		To make this permanent, add {{nixos:package\|ddcutil}} to your system packages, and enable i2c support.<syntaxhighlight lang="nix">

Natejank: Give explicit instructions for which group is needed to use DDC/CI, or which udev rules should be set to do the same. Based on https://github.com/NixOS/nixpkgs/issues/292049#issuecomment-2618103666

2026-01-26T17:55:03Z

Give explicit instructions for which group is needed to use DDC/CI, or which udev rules should be set to do the same. Based on https://github.com/NixOS/nixpkgs/issues/292049#issuecomment-2618103666

← Older revision		Revision as of 17:55, 26 January 2026
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	</syntaxhighlight>		</syntaxhighlight>

	You can then bind this to a hotkey or similar. ~~<code>sudo</code> may be avoidable if your user is in the correct group, or udev rules have set the appropriate <code>/sys</code> permissions.~~		You can then bind this to a hotkey or similar.



	To make this permanent, add {{nixos:package\|ddcutil}} to your system packages, and enable i2c support.<syntaxhighlight lang="nix">		To make this permanent, add {{nixos:package\|ddcutil}} to your system packages, and enable i2c support.<syntaxhighlight lang="nix">
	hardware.i2c.enable = true		hardware.i2c.enable = true
	</syntaxhighlight>		</syntaxhighlight>To interact with DDC/CI without root, also add your user to the <code>i2c</code> group (or the group defined by <code>[https://search.nixos.org/options?show=hardware.i2c.group&query=hardware.i2c.group hardware.i2c.group]</code>), or [https://www.ddcutil.com/i2c_permissions/ set udev rules manually].

	=== Via <code>ddcci-driver</code> ===		=== Via <code>ddcci-driver</code> ===

Kittyd at 21:07, 27 January 2025

2025-01-27T21:07:09Z

← Older revision		Revision as of 21:07, 27 January 2025
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	You can then bind this to a hotkey or similar. <code>sudo</code> may be avoidable if your user is in the correct group, or udev rules have set the appropriate <code>/sys</code> permissions.		You can then bind this to a hotkey or similar. <code>sudo</code> may be avoidable if your user is in the correct group, or udev rules have set the appropriate <code>/sys</code> permissions.

	~~Add <code>i2c-dev</code> to <code>boot.kernelModules</code> and~~ {{nixos:package\|ddcutil}} to your system packages ~~to make permanent~~.		To make this permanent, add {{nixos:package\|ddcutil}} to your system packages, and enable i2c support.<syntaxhighlight lang="nix">
			hardware.i2c.enable = true
			</syntaxhighlight>

	=== Via <code>ddcci-driver</code> ===		=== Via <code>ddcci-driver</code> ===

Hughobrien: add source link to ddcci overlay

2024-11-02T17:05:20Z

add source link to ddcci overlay

← Older revision		Revision as of 17:05, 2 November 2024
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	Device autodetection is tricky with i2c so we need to trigger it manually with the <code>0x37</code> code. The <code>sleep</code> is often unfortunately necessary.		Device autodetection is tricky with i2c so we need to trigger it manually with the <code>0x37</code> code. The <code>sleep</code> is often unfortunately necessary.

	The driver has had some issues with kernels > 6.8, the below overlay should allow it to build if you encounter issues.		The driver has had some issues with kernels > 6.8, the below overlay should allow it to build if you encounter issues ([https://gitlab.com/ddcci-driver-linux/ddcci-driver-linux/-/merge_requests/17 source]).

	<syntaxhighlight lang=nix>		<syntaxhighlight lang=nix>

Hughobrien: add note about auto loading the i2c module

2024-11-02T17:02:33Z

add note about auto loading the i2c module

← Older revision		Revision as of 17:02, 2 November 2024
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	You can then bind this to a hotkey or similar. <code>sudo</code> may be avoidable if your user is in the correct group, or udev rules have set the appropriate <code>/sys</code> permissions.		You can then bind this to a hotkey or similar. <code>sudo</code> may be avoidable if your user is in the correct group, or udev rules have set the appropriate <code>/sys</code> permissions.

			Add <code>i2c-dev</code> to <code>boot.kernelModules</code> and {{nixos:package\|ddcutil}} to your system packages to make permanent.

	=== Via <code>ddcci-driver</code> ===		=== Via <code>ddcci-driver</code> ===

Hughobrien: Add section on controlling external monitors

2024-11-02T16:56:45Z

Add section on controlling external monitors

← Older revision		Revision as of 16:56, 2 November 2024
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	Example: <code>brightnessctl set 5%- -d intel_backlight</code>		Example: <code>brightnessctl set 5%- -d intel_backlight</code>

			== External Monitors ==

			The DDC/CI (I2C) interface may be available to control the brightness of your external monitor. There are two ways to do this:

			=== Via <code>ddcutil</code> ===
			<syntaxhighlight lang=shell>
			$ sudo modprobe i2c-dev
			$ nix-shell -p ddcutil --command "sudo ddcutil --bus=MYBUSNUM setvcp 10 MYBRIGHTNESSPCT"
			</syntaxhighlight>

			You can find the correct bus number by examining the paths in <code>/sys/bus/i2c/devices</code>. e.g. to control the <code>DP4</code> device below use device <code>17</code>.

			<syntaxhighlight lang=shell>
			$ ls -l /sys/bus/i2c/devices/
			lrwxrwxrwx - root 2 Nov 12:34 i2c-13 -> ../../../devices/pci0000:00/0000:00:02.0/drm/card1/card1-eDP-1/i2c-13
			lrwxrwxrwx - root 2 Nov 12:34 i2c-14 -> ../../../devices/pci0000:00/0000:00:02.0/drm/card1/card1-DP-1/i2c-14
			lrwxrwxrwx - root 2 Nov 12:34 i2c-15 -> ../../../devices/pci0000:00/0000:00:02.0/drm/card1/card1-DP-2/i2c-15
			lrwxrwxrwx - root 2 Nov 12:34 i2c-16 -> ../../../devices/pci0000:00/0000:00:02.0/drm/card1/card1-DP-3/i2c-16
			lrwxrwxrwx - root 2 Nov 12:34 i2c-17 -> ../../../devices/pci0000:00/0000:00:02.0/drm/card1/card1-DP-4/i2c-17
			</syntaxhighlight>

			All together: <syntaxhighlight lang=shell>
			nix-shell -p ddcutil --command "sudo ddcutil --bus=17 setvcp 10 65"
			</syntaxhighlight>

			You can then bind this to a hotkey or similar. <code>sudo</code> may be avoidable if your user is in the correct group, or udev rules have set the appropriate <code>/sys</code> permissions.

			=== Via <code>ddcci-driver</code> ===
			A [https://gitlab.com/ddcci-driver-linux/ddcci-driver-linux driver] exists which exposes the ddcci control as a more standard <code>backlight</code> device, allowing it to be controlled by standard utilities such as <code>brightnessctl</code>. e.g. when setup:

			<syntaxhighlight lang=shell>
			$ find /sys/class/backlight
			/sys/class/backlight
			/sys/class/backlight/ddcci17
			/sys/class/backlight/intel_backlight

			$ brightnessctl --device=ddcci17 set 100%
			Updated device 'ddcci17':
			Device 'ddcci17' of class 'backlight':
			Current brightness: 100 (100%)
			Max brightness: 100

			</syntaxhighlight>

			Get the i2c name:
			<syntaxhighlight lang=shell>
			$ cat /sys/bus/i2c/devices/i2c-17/name
			AUX USBC4/DDI TC4/PHY TC4
			</syntaxhighlight>

			<syntaxhighlight lang=nix>
			boot.extraModulePackages = with config.boot.kernelPackages; [ ddcci-driver ];
			boot.kernelModules = [ "ddcci-backlight" ];
			services.udev.extraRules = let
			bash = "${pkgs.bash}/bin/bash";
			ddcciDev = "AUX USBC4/DDI TC4/PHY TC4";
			ddcciNode = "/sys/bus/i2c/devices/i2c-17/new_device";
			in ''
			SUBSYSTEM=="i2c", ACTION=="add", ATTR{name}=="${ddcciDev}", RUN+="${bash} -c 'sleep 30; printf ddcci\ 0x37 > ${ddcciNode}'"
			'';
			</syntaxhighlight>

			Device autodetection is tricky with i2c so we need to trigger it manually with the <code>0x37</code> code. The <code>sleep</code> is often unfortunately necessary.

			The driver has had some issues with kernels > 6.8, the below overlay should allow it to build if you encounter issues.

			<syntaxhighlight lang=nix>
			nixpkgs.overlays = [
			(self: super: {
			linuxPackages_latest = super.linuxPackages_latest.extend (lpself: lpsuper: {
			ddcci-driver = super.linuxPackages_latest.ddcci-driver.overrideAttrs (oldAttrs: {
			version = super.linuxPackages_latest.ddcci-driver.version + "-FIXED";
			src = pkgs.fetchFromGitLab {
			owner = "ddcci-driver-linux";
			repo = "ddcci-driver-linux";
			rev = "0233e1ee5eddb4b8a706464f3097bad5620b65f4";
			hash = "sha256-Osvojt8UE+cenOuMoSY+T+sODTAAKkvY/XmBa5bQX88=";
			};
			patches = [
			(pkgs.fetchpatch {
			name = "ddcci-e0605c9cdff7bf3fe9587434614473ba8b7e5f63.patch";
			url = "https://gitlab.com/nullbytepl/ddcci-driver-linux/-/commit/e0605c9cdff7bf3fe9587434614473ba8b7e5f63.patch";
			hash = "sha256-sTq03HtWQBd7Wy4o1XbdmMjXQE2dG+1jajx4HtwBHjM=";
			})
			];
			});
			});
			})
			];
			</syntaxhighlight>

	== <code>/sys/class/backlight/...</code> ==		== <code>/sys/class/backlight/...</code> ==

Klinger: link to category instead of redirect page

2024-07-01T21:07:54Z

link to category instead of redirect page

← Older revision		Revision as of 21:07, 1 July 2024
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	While controlling the backlight via the command line is useful, it would be preferable to control it using key bindings. This is especially true considering most laptops have backlight control keys.		While controlling the backlight via the command line is useful, it would be preferable to control it using key bindings. This is especially true considering most laptops have backlight control keys.

	There are two main choices to add key bindings, using a system-level service like [[actkbd]] or using an X session tool, either provided by your [[Desktop environment]], [[Window manager]] or a tool like [[xbindkeys]].		There are two main choices to add key bindings, using a system-level service like [[actkbd]] or using an X session tool, either provided by your [[:Category:Desktop environment\|Desktop environment]], [[Window manager]] or a tool like [[xbindkeys]].

	Depending on the tools that work for controlling the backlight you will be able to choose one of those options.		Depending on the tools that work for controlling the backlight you will be able to choose one of those options.

imported>RamReso: added example for brightnessctl and added a note for device of brightnessctl

2023-12-19T17:13:29Z

added example for brightnessctl and added a note for device of brightnessctl

← Older revision		Revision as of 17:13, 19 December 2023
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	You can use it by simply installing the package. Since <code>brightnessctl</code> supports the systemd-logind API it should work out of the box (i.e. without installing any udev rules or using a setuid wrapper).		You can use it by simply installing the package. Since <code>brightnessctl</code> supports the systemd-logind API it should work out of the box (i.e. without installing any udev rules or using a setuid wrapper).

			The following commands will allow you to test <code>brightnessctl</code>:
			* <code> brightnessctl set 5%-</code> - the screen should become darker.
			* <code> brightnessctl set 5%+</code> - the screen should become brighter.

			If you get an error like <code>Failed to set brightness: Protocol error</code>, check that you are using the right device. You can get a list of the devices with running <code>brightnessctl -l</code> and then specify the device with <code>-d deviceName</code>.

			Example: <code>brightnessctl set 5%- -d intel_backlight</code>

	== <code>/sys/class/backlight/...</code> ==		== <code>/sys/class/backlight/...</code> ==

imported>Vater: form (fixing :Category:Pages with syntax highlighting errors) and add a first (content) category

2022-01-05T06:04:02Z

form (fixing Category:Pages with syntax highlighting errors) and add a first (content) category

← Older revision		Revision as of 06:04, 5 January 2022
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	programs.light.enable = true;		programs.light.enable = true;
	</syntaxhighlight>		</syntaxhighlight>



	The following commands will allow you to test <code>light</code>:		The following commands will allow you to test <code>light</code>:
	*<code>light -U 30</code> — the screen should become darker.		* <code>light -U 30</code> — the screen should become darker.
	*<code>light -A 30</code> — the screen should become brighter.		* <code>light -A 30</code> — the screen should become brighter.

	Be careful using <code>light -U</code>, as you might turn your backlight completely off! You will not be able to see what you're typing anymore.		Be careful using <code>light -U</code>, as you might turn your backlight completely off! You will not be able to see what you're typing anymore.

	== <code>brightnessctl</code> ==		== <code>brightnessctl</code> ==

	{{nixos:package\|brightnessctl}} ([https://github.com/Hummer12007/brightnessctl homepage]) is another option, which, like <code>light</code>, would work even without X or on Wayland.		{{nixos:package\|brightnessctl}} ([https://github.com/Hummer12007/brightnessctl homepage]) is another option, which, like <code>light</code>, would work even without X or on Wayland.

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	== <code>/sys/class/backlight/...</code> ==		== <code>/sys/class/backlight/...</code> ==

	The <code>/sys/class/backlight/*/brightness</code> files are a built-in way to set brightness. Use them e.g. with:		The <code>/sys/class/backlight/*/brightness</code> files are a built-in way to set brightness. Use them e.g. with:

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	to set the brightness to <code>300</code>, where the maximum is stored in <code>brightness_max</code>. You can set file permissions e.g. with a udev rule, if you don't want to use sudo. Here is an example udev rule, where you will likely have to replace intel_backlight, with the name in your /sys/class/backlight/:		to set the brightness to <code>300</code>, where the maximum is stored in <code>brightness_max</code>. You can set file permissions e.g. with a udev rule, if you don't want to use sudo. Here is an example udev rule, where you will likely have to replace intel_backlight, with the name in your /sys/class/backlight/:

	<syntaxhighlight lang=~~udev~~>		<syntaxhighlight lang=nix>
	services.udev.extraRules = ''		services.udev.extraRules = ''
	ACTION=="add", SUBSYSTEM=="backlight", KERNEL=="intel_backlight", MODE="0666", RUN+="${pkgs.coreutils}/bin/chmod a+w /sys/class/backlight/%k/brightness"		ACTION=="add", SUBSYSTEM=="backlight", KERNEL=="intel_backlight", MODE="0666", RUN+="${pkgs.coreutils}/bin/chmod a+w /sys/class/backlight/%k/brightness"
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	Depending on the tools that work for controlling the backlight you will be able to choose one of those options.		Depending on the tools that work for controlling the backlight you will be able to choose one of those options.

	{\| class="wikitable~~" border="1~~"		{\| class="wikitable"
	\|-		\|-
	!		!
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	* NixOS 19.09pre173166.373488e6f4c on a Lenovo X240		* NixOS 19.09pre173166.373488e6f4c on a Lenovo X240

	it may work on other models, but is unconfirmed. See [[actkbd]] for details on finding out the proper key bindings. Also check if the path to the light binary is correct. }}		it may work on other models, but is unconfirmed. See [[actkbd]] for details on finding out the proper key bindings. Also check if the path to the light binary is correct.}}



	<syntaxhighlight lang="nix">		<syntaxhighlight lang=nix>
	programs.light.enable = true;		programs.light.enable = true;
	services.actkbd = {		services.actkbd = {
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	== OLED Screens ==		== OLED Screens ==

	OLED screens do not have a backlight, but their perceived brightness can be changed via xrandr:		OLED screens do not have a backlight, but their perceived brightness can be changed via xrandr:

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	* [https://wiki.archlinux.org/index.php/backlight Arch Linux wiki page about the backlight]		* [https://wiki.archlinux.org/index.php/backlight Arch Linux wiki page about the backlight]

			[[category:hardware]]

imported>Con-f-use: example udev rule for /sys/class method

2020-07-09T11:48:43Z

example udev rule for /sys/class method

← Older revision		Revision as of 11:48, 9 July 2020
Line 50:		Line 50:
	</syntaxhighlight>		</syntaxhighlight>

	to set the brightness to <code>300</code>, where the maximum is stored in <code>brightness_max</code>. You can set file permissions e.g. with a udev rule, if you don't want to use sudo.		to set the brightness to <code>300</code>, where the maximum is stored in <code>brightness_max</code>. You can set file permissions e.g. with a udev rule, if you don't want to use sudo. Here is an example udev rule, where you will likely have to replace intel_backlight, with the name in your /sys/class/backlight/:

			<syntaxhighlight lang=udev>
			services.udev.extraRules = ''
			ACTION=="add", SUBSYSTEM=="backlight", KERNEL=="intel_backlight", MODE="0666", RUN+="${pkgs.coreutils}/bin/chmod a+w /sys/class/backlight/%k/brightness"
			'';
			</syntaxhighlight>

	== Tips ==		== Tips ==