KDE Plasma Widget for external monitor brightness adjustment

Setup

1. Load the i2c-dev kernel module

Note: Most kernel builds should include this module by default.

Check if it is already loaded:

$ lsmod | grep i2c_dev

If it isn't, load it automatically on every boot:

$ echo i2c-dev | sudo tee /etc/modules-load.d/i2c-dev.conf

or load it once:

$ sudo modprobe i2c-dev

2. Install and configure ddcutil

ddcutil is a commandline utility to control external monitors. This widget uses ddcutil to detect supported monitors and adjust their brightness. For additional details, refer to the great ddcutil documentation. Note that additional steps may be required if you are using a NVIDIA GPU, see Special Nvidia Driver Settings in the ddcutil documentation.

Install the ddcutil from your distribution's repositories. (Arch Linux)

By default, ddcutil can only be used by the root user. Little configuration is required to allow non-root users to use it:

$ sudo usermod -aG i2c <username>

If the group i2c doesn't exit, create it first:

$ sudo groupadd --system i2c

Finally, you need to install a udev rule to allow members of the group i2c to access to i2c devices:

$ sudo cp /usr/share/ddcutil/data/45-ddcutil-i2c.rules /etc/udev/rules.d

Now, you can verify that ddcutil is working correctly:

$ ddcutil detect

The output should look something like that:

Display 1
   I2C bus:  /dev/i2c-9
   DRM connector:           card0-DP-1
   EDID synopsis:
      Mfg id:               DEL - Dell Inc.
      Model:                DELL S2721DGF
      Product code:         XXXXX  (0xXXXX)
      Serial number:        XXXXXXXX
      Binary serial number: XXXXXXXX (0xXXXXXXXX)
      Manufacture year:     2022,  Week: 35
   VCP version:         2.1

Display 2
   I2C bus:  /dev/i2c-10
   DRM connector:           card0-DP-2
   EDID synopsis:
      Mfg id:               DEL - Dell Inc.
      Model:                DELL U2417H
      Product code:         XXXXX  (0xXXXX)
      Serial number:        XXXXXXXX
      Binary serial number: XXXXXXXX (0xXXXXXXXX)
      Manufacture year:     2018,  Week: 22
   VCP version:         2.1

3. Install the backend

pip install ddcci-plasmoid-backend

4. Install the widget itself

Install the widget from the official KDE Store, or install it manually:

$ git clone https://github.com/davidhi7/ddcci-plasmoid.git
$ cd ddcci-plasmoid
$ kpackagetool5 --install plasmoid
# or upgrade the plasmoid:
$ kpackagetool5 --upgrade plasmoid