DeviceKit-power and backlight brightness

[Richard Hughes]

As we all know, the hal-ectimisation continues. At the moment,
gnome-power-manager still uses HAL for two things:

* Ambient light sensors
* Setting the backlight on hardware without xrandr BRIGHTNESS support,
or where xrandr falls over

Now, I've held off adding support for backlight devices to
DeviceKit-power in the past, as I always believed that xrandr was the
way to go long term. Unfortunately, I think only the Intel Xorg driver
has support for this interface, and it seems to work only for select
drm versions (and depending on the phase of the moon). Therefore, I
think we need to support kernel backlight devices as these still
account for the majority of laptops, and nearly all embedded hardware.

And then there are ambient light sensors. HAL supports a few different
types, but that would be pretty easy to copy the code and move it
somewhere else.

So, some questions:

* Do we still need to support backlight devices, even in a XBACKLIGHT world?
* Does the brightness functionality belong in DeviceKit-power or
something else (DeviceKit-backlight?)
* Do we want to move the ambient light sensor stuff at the same time?
* Do we support hardware with more than one backlight device
(shouldn't, but could happen)

Advice required. Thanks.

Richard.