Can't set backlight brightness

spira_mirabilis · 2017-05-29 19:41:47

Hi, I'm new to Arch 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:
uname -r: 4.11.2-1-ARCH
lspci -v: https://pastebin.com/RWymtnZ2
lsmod: https://pastebin.com/fQWvrkdB
dmesg: https://pastebin.com/msnaa73a

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

uname -r: 4.8.6-300.fc25.x86_64
lspci -v: https://pastebin.com/3DVfZf4e
lsmod: https://pastebin.com/GyQyA4yY
dmesg: https://pastebin.com/AC1ufiDM

Thank you in advance for your help.

Feel free to correct my english!

Last edited by spira_mirabilis (2017-05-30 19:58:06)

olegabrielz · 2017-05-30 08:28:09

Find maximum value with:

cat /sys/class/backlight/acpi_video0/max_brightness

Set set value with:

tee /sys/class/backlight/acpi_video0/brightness <<< 10

https://wiki.archlinux.org/index.php/backlight#ACPI

spira_mirabilis · 2017-05-30 08:33:33

The maximum value is 100.
As I wrote in my first post, changing the value of /sys/class/backlight/acpi_video0/brightness doesn't affect the display brightness at all.

olegabrielz · 2017-05-30 08:37:19

You said you did use echo to change it, not the tee command. Echo does not work for me either, but tee does.

spira_mirabilis · 2017-05-30 08:43:14

I rephrase: setting the value of /sys/class/backlight/acpi_video0/brightness in any way (echo, tee) the value of the file changes, but that doesn't affect the display brightness.

olegabrielz · 2017-05-30 08:53:08

Sorry for not being helpful. I just noticed that the echo command did not change brightness on my computer, but tee did. Hopefully someone here can help you solve this.

spira_mirabilis · 2017-05-30 08:57:08

Thanks for trying to help me anyway!

spira_mirabilis · 2017-05-30 19:58:58

I edited the question with the specs of a live Fedora 25. I couldn't spot any useful differences, can anyone do it?

Head_on_a_Stick · 2017-05-30 20:47:49

spira_mirabilis wrote:

I tried setting this argument acpi_backlight=vendor to the kernel.

Did you try the other parameters?

https://wiki.archlinux.org/index.php/Ba … ne_options

spira_mirabilis · 2017-05-30 21:12:54

Yes, with no success.

spira_mirabilis · 2017-05-31 19:23:26

I switched to linux-lts kernel and it works like a charm.

Head_on_a_Stick · 2017-06-01 18:52:39

If you want the next LTS branch to work with your hardware it may be worth bisecting the kernel to track down the regression that has caused the problem.

https://wiki.archlinux.org/index.php/Bisecting_bugs

Arch Linux

#1 2017-05-29 19:41:47

Can't set backlight brightness

#2 2017-05-30 08:28:09

Re: Can't set backlight brightness

#3 2017-05-30 08:33:33

Re: Can't set backlight brightness

#4 2017-05-30 08:37:19

Re: Can't set backlight brightness

#5 2017-05-30 08:43:14

Re: Can't set backlight brightness

#6 2017-05-30 08:53:08

Re: Can't set backlight brightness

#7 2017-05-30 08:57:08

Re: Can't set backlight brightness

#8 2017-05-30 19:58:58

Re: Can't set backlight brightness

#9 2017-05-30 20:47:49

Re: Can't set backlight brightness

#10 2017-05-30 21:12:54

Re: Can't set backlight brightness

#11 2017-05-31 19:23:26

Re: Can't set backlight brightness

#12 2017-06-01 18:52:39

Re: Can't set backlight brightness

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