[Libreboot] Brightness adjustment on Parabola (Arch) GNU/Linux for X200 Libreboot

[Filippo]

Dear libreboot community, congratulations and big thanks to the devs and 
maintainers.

I'm trying to get brightness keys to work on my X200 running libreboot 
(rel 20150518). They work perfectly on Trisquel or Debian, but *not* in 
Arch or Parabola with standard 4.x kernel (linux-libre, 
linux-libre-lts). So I was wondering if the collective knowledge of the 
alias could help me here :)

The only way I could eventually work around brightness keys to work on 
my Parabola install was by using acpid and having a script intercept the 
key presses (you can find a reference to the principle I used here 
https://wiki.archlinux.org/index.php/Acpid#Enabling_backlight_control).

Before going that way, I tried without luck to pass all the various 
kernel options as mentioned in this document:
https://mzanfardino.wordpress.com/2015/02/10/linux-enabling-brightness-control-for-thinkpad-w520/
after I noticed the dmesg log:

thinkpad_acpi: Lenovo ThinkPad X200, model 74591P0
thinkpad_acpi: detected a 8-level brightness capable ThinkPad
thinkpad_acpi: This ThinkPad has standard ACPI backlight brightness 
control, supported by the ACPI video driver
thinkpad_acpi: Disabling thinkpad-acpi brightness events by default...
thinkpad_acpi: Standard ACPI backlight interface available, not loading 
native one

(without any kernel option, under /sys/class/backlight I only have 
intel_backlight).

Any experience on your side that could be useful in resolving this 
situation?
It's not a big deal, I'm just curious to get the brightness keys working 
in console mode with native kernel support instead of acpid :)

Warm regards,

--
Fil
[happy libreboot user, reboot-tuesday advocate]