Re: Questions on adding backlight support for the i915 driver

On 1/28/15 1:38 AM, Elizabeth Myers wrote:
> 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.

Humm.  If the code is going to live in the drm driver, then I would
start with hanging a sysctl off of the drm device itself.  (Each new-bus
device_t has a sysctl ctx you can get to hang new nodes off of the
device's node.)

-- 
John Baldwin