Some weeks ago I switched to Arch in my notebook Toshiba Satellite L845D, and one of the first problems I've got was that my Fn keys that control the screen brightness weren't working (the rest worked just fine), so (after some days) I started to look for a solution.
- The first step was to install a package (which I'm not completely sure it's necessary) named gnome-settings-daemon-backlight-toshiba. To do this, we have to use AUR.
Or we can search for it..
- Now we have to edit a line in our grub. You can use nano, gedit, mousepad, etc.
Now in the line GRUB_CMDLINE_LINUX we have to add acpi_osi=Linux and acpi_backlight=video. The value of the last one, acpi_backlight=video can vary depending on your hardware. These are the possible options:
The line should look similar to this one:
- Save and close. Now update grub with the following command:
Or for the ones used to update-grub..
And thats it, just reboot and try it out.
For more information about the topic here is a link to the ArchWiki - Backlight section, where you can find the values I gave you above and much more.
Hope it helps!