Bug#822443: Acknowledgement (linux-image-4.4.0-1-amd64: Dell XPS-13 9350 (DE) backlight not detected)

[Ian Jackson <ijackson@chiark.greenend.org.uk>]

I have since discovered that:

 * On this machine the i915 driver is responsible for the backlight
   control too.

 * The i915 driver registers the backlight device in the modesetting
   path (!)

 * Although "nomodeset" was required to get the kernel from stretch
   Alpha 5 to not produce a black screen shortly after booting into
   the installed system, linux-image-4.4.0-1-amd64 4.4.6-1 works fine
   without "nomodeset" (and seems to set the mode during boot as
   expected).  There seems little point in reporting any bug against
   the stretch alpha 5 kernel as I'm sure it will be updated in due
   course.

 * Booting linux-image-4.4.0-1-amd64 4.4.6-1 without "nomodeset"
     - produces /sys/class/backlight/intel_backlight
        and working backlight control buttons
     - seems to suspend and resume fine (4 trials so far)

I will close this bug.  Sorry for the noise.

Ian.