[Trisquel-users] Brightness control

[hbb2]

I have an Acer ASPIRE M5 481T and can't adjust the screen brightness. It came  
with windows 8 pre-installed which I removed.

I used xbacklight and got  "No outputs have backlight property"
Tried "setpci -s 00:02.0 f4.b=XX" without success.

Also changed the bootloader parameters with "acpi_backlight=vendor" and  
didn't work.

What can I do? Thank you.