Unable to adjust brightness on amd CPU with integrated GPU

Support Graphics & Display
6

** Edit 21/01/21 23:14 CST: This method will not work after a system restart. Investigating solution. **
** Edit 21/01/22 20:10 CST: A workaround for above issue had been found. **

Well, I have a temporary workaround with xrandr, inotifywait, and systemd.
The idea is watching brightness modification, and then apply it with xrandr.

Depends on:

  • inotify-tools package.
  • Screen brightness can be adjusted by xrandr.

Step:

  1. Edit /usr/local/bin/adjust_brightness and make it executable

    #!/bin/sh

bl_dev=/sys/class/backlight/amdgpu_bl1  # Modify device path to meet your brand

ratio=$(echo $(<$bl_dev/brightness) / $(<$bl_dev/max_brightness) | bc -l)
xrandr --output eDP --brightness $ratio

  2. Edit ~/.config/systemd/user/adjust-brightness.service

    [Unit]
Description=Adjust Screen Brightness

[Service]
Type=simple
ExecStart=/bin/bash -c "while true; do inotifywait -q -e modify /sys/class/backlight/amdgpu_bl1/brightness; /usr/local/bin/adjust_brightness; done"

[Install]
WantedBy=default.target

  3. Edit ~/.config/autostart/brightness-adjuster.desktop

    [Desktop Entry]
Name=Brightness Adjuster
Exec=systemctl --user start adjust-brightness
Type=Application
Terminal=false
Comment=Adjust Brightness

I’m using Lenovo Legion 5 15ARH05H with Manjaro KDE 20.2.1 (5.10.7-3-MANJARO).
Please let me know if this method works for others too.
Further discussion is welcome.

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