Questions on adding backlight support for the i915 driver

Hello,

I want to add backlight support to the i915 driver in FreeBSD. It seems
that two magic addresses are read and wrote from to change the backlight
itself. It supports rather fine-level granularity all the way down to
zero. Right now I use a hacked-up userland program that reads
from/writes to these addresses, which is far from an ideal solution.

I am interested in this because the acpi_video(4) driver does not
support my backlight on my Dell Inspiron 15 3521 (not terribly
suprising, on Linux I needed a special Dell-specific driver, and I'm not
sure even that really used ACPI, I never really checked).

My questions are really twofold:

1) How can this be exposed appropriately? I would prefer this be exposed
generally so upower could grok it. As far as I can tell upower uses
hw.acpi.video.lcd0 to control backlight. I am not sure that upower is
doing the "right" thing here, though.
2) Where would the code go for this? The dri2 driver seems the most
"logical" place, but maybe it belongs in X and exposed via a program? Or
something else entirely that I'm not thinking of?

I have experience developing PCI drivers and doing other PCI related
doodads, and some kernel development experience, as well as general C
experience, but I'm not by any means an expert on the matter.

Cheers,
Elizabeth Myers