ASUS Zenbook S14 (UX5406AA) backlight issues

I recently got this laptop after my Slimbook Pro X 15 had a hardware failure.

I encountered a couple of issues when trying to use Linux. Two of them were particularly painful:

• I couldn’t modify the screen’s brightness
• Speakers don’t work

If you encounter the backlight issue, try putting this into your boot arguments [1]: xe.enable_dpcd_backlight=1

You can first test if this solves the issue by specifying it as a one-time boot argument in the grub boot menu. If it works, just place it under /etc/default/grub/

1GRUB_CMDLINE_LINUX="... xe.enable_dpcd_backlight=1"

And regenerate your grub file.

This was a though find because all the documentation I saw mentioned i915.enable_dpcd_backlight. It seems the new Xe driver implicitly inherits some of i915’s configuration parameters. Information on what might cause the issue can be found here [2].

[1] https://www.mail-archive.com/ubuntu-bugs@lists.ubuntu.com/msg6257024.html

[2] https://gitlab.freedesktop.org/drm/xe/kernel/-/work_items/7681