Bug 51593

I was hoping by known that we would have had a generic solution to finding the right backlight controller...

commit 61e16dc5673a1ac96b2ecee072cc3e80971be5d9
Author: Tom Hughes <tom@compton.nu>
Date:   Mon Jul 2 10:23:56 2012 +0100

    Add asus-nb-wmi backlight control
    
    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=51593

Thanks for the patch!

Well one component (gnome-settings-daemon) that I investigated in the long chain between gnome-control-center and the X driver was doing a search of /sys/class/backlight and looking at the type of each one, with "firmware" taking first priority, followed by "platform" and finally "raw".

I believe that "firmware" is the manufacturer specific ones, "platform" is the generic ACPI interfaces and "raw" is the low level ones like intel_backlight which would mean that search would give basically the same results as the current hard coded list?

Ah, I see you've just done that ;-)

Right, the 'type' qualifier was added for libbacklight (http://cgit.freedesktop.org/libbacklight/) with which Matthew was trying to create a generic solution that with a little more help from the kernel could associate the right backlight controller for any particular output. It never quite materialized into a finished piece of code.

Indeed, I added code to scan /sys/class/backlight/*/type and pick the firmware interfaces (firmare > platform > raw) and only fallback to the known list for older kernels. Which at least should avoid the problem of detecting new controllers, but not yet addressing hybrid systems or multiple controllers.