ThinkPad T520 backlight brightness hotkeys and Xfce slider not working in Linux (Xubuntu 17.04)

The LCD backlight brightness controls for my new laptop (Lenovo Thinkpad T520, replacing the Edge 15 I used before) don't work on Linux at all. I can adjust brightness using the keyboard shortcuts (Fn + Home or End) during the boot sequence but when Linux takes over from the boot loader, these hotkeys no longer work and neither does Xfce's brightness GUI or the xbacklight command line tool I installed. Some Googling revealed multiple contradictory answers that involved digging in config files I really would rather not dig into unless I'm certain the procedure would work. One site said this is apparently a problem with newer kernel versions breaking something about the ThinkPad ACPI driver. Does anybody here know about this problem?

It appears that the functionality is not complete in Linux. It doesn't look like Lenovo supports that in Linux.

I don't have my W520 booted up to check but the T61 I'm on now has a brightness control in BIOS.

I already said the brightness controls work when the BIOS is running, but when it hands the computer over to Linux, they stop working. Also, does Lenovo even write Linux drivers? I've heard people say that ThinkPad brightness controls used to work but a kernel update broke them.

Originally Posted by Woolie Wool I already said the brightness controls work when the BIOS is running, but when it hands the computer over to Linux, they stop working.

No, what you said was:

I can adjust brightness using the keyboard shortcuts (Fn + Home or End) during the boot sequence but when Linux takes over from the boot loader, these hotkeys no longer work and neither does Xfce's brightness GUI or the xbacklight command line tool I installed.

I said there is a brightness control in the BIOS settings of my T61. Nothing about pressing Fn + Home or End.

There probably is in mine too, but how is that useful for this thread?

Originally Posted by Woolie Wool There probably is in mine too, but how is that useful for this thread?

Then excuse me for wasting your time. I won't disrupt your thread further and leave you to it.

This is a well-known problem, but you may find a fix that works here:
http://www.thinkwiki.org/wiki/Proble...htness_buttons

Thanks for the link, I've only tried the /etc/linux/grub solution so far (didn't work), but I'll try the others later.

Originally Posted by Woolie Wool Thanks for the link, I've only tried the /etc/linux/grub solution so far (didn't work), but I'll try the others later.

... There is also a command-line solution to operate on screen brightness if you can't get the buttons to work. Let us know if you need to go there ...

Cheers,

Does the /sys/class/backlight/ stuff work for you? You can echo values there when all else fails.

FILE: /etc/default/grub

GRUB_CMDLINE_LINUX_DEFAULT="quiet acpi=force acpi_backlight=vendor"

Where "quiet" was there originally. The change updates the grub.cfg to pass those options to the linux kernel and makes the /sys/class/backlight/... options exist.

$ cat /sys/class/backlight/amdgpu_bl0/brightness

$ cat /sys/class/backlight/amdgpu_bl0/max_brightness
255

$ sudo chown $(whoami):$(whoami) /sys/class/backlight/amdgpu_bl0/brightness
$ echo 128 > /sys/class/backlight/amdgpu_bl0/brightness

Your subpath might vary depending on your GPU, like intel_backlight/ versus amdgpu_bl0/ et cetera. And in two years when various distros catch up, it'll just work out of the box.

When things just work, you can do this:

$ xbacklight -set 50%