Can't set backlight brightness

I'm trying Arch Linux and I'm stuck with this problem: I can't set the brightness of my laptop display. I read https://wiki.archlinux.org/index.php/backlight and other troubleshooting pages about this topic, but I didn't find a solution yet. The directory /sys/class/backlight contains only the acpi_video0 directory. Setting a value to the brightness file doesn't affect the brightness of the display:

echo 50 > /sys/class/backlight/acpi_video0/brightness

Booting my laptop with other distros (Fedora, Debian), the directory /sys/class/backlight contains also the intel_backlight directory. Setting a value to the brightness file, the brightness changes like I was expecting. I tried setting this argument acpi_backlight=vendor to the kernel. The result was that the directory /sys/class/backlight was empty.

Here some specs about my installed Arch:

uname -r: 4.11.2-1-ARCH

lspci -v: (output in pastebin)

lsmod: (output in pastebin)

dmesg: (output in pastebin)

Specs from a live Fedora 25 (where the brightness works):

uname -r: 4.8.6-300.fc25.x86_64

lspci -v: (output in pastebin)

lsmod: (output in pastebin)

dmesg: (output in pastebin)

Thank you in advance for your help.

Denis Frezzato

Posted 2017-05-29T19:46:37.653

Reputation: 146

Very likely your Arch Linux is missing the intel driver for the backlight. Update your kernel. If that doesn't help, compare kernel versions and dmesg output between Arch Linux and the distros where it works, and find where the difference is. – dirkt – 2017-05-30T07:51:43.497

@dirkt the kernel is already updated. I edited the question with the specs of a live Fedora 25. I couldn't spot any useful info from dmesg, can anyone do it? – Denis Frezzato – 2017-05-30T19:55:13.740

Looked at the source, and intel_backlight is provided by the i915 driver. Which seems to load properly in both cases. Looked at the history in git, and while there are some changes, there's no obvious one that would cause it to disappear. Options: (1) Try different earlier kernels on Arch, see if and for which kernel version it comes back. (2) Compile kernel on Arch, enable DRM_I915_DEBUG, see if the extra information turns up something. (3) File a bug with the i915 kernel developers.

– dirkt – 2017-05-31T07:00:54.057

I switched to linux-lts (4.9.30-1-lts) and it works like a charm! Thank you @dirkt for your tips! – Denis Frezzato – 2017-05-31T19:22:45.137

Please still file a bug, this needs to be fixed. – dirkt – 2017-05-31T21:51:19.560

Sure, I will! ;) – Denis Frezzato – 2017-06-01T06:00:57.647

Can't set backlight brightness

No answers