I'm a little unsure as to what I need to install to get

nv_backlight

to show up. I have downloaded both

libdrm-nouveau2

and

xserver-xorg-video-nouveau

but there's still nothing there. Do I need anything else? I've tried

acpi_backlight=vendor

and

acpi_backlight=video

in GRUB_CMDLINE_LINUX as well, to no avail. By the way I should tell you that it's a laptop with a NVIDIA GeForce 8600M GT GPU, using nouveau as getting the 340xx drivers working turned out to be quite a pain and honestly impossible.