kern/50789: drmkms backlight/brightness controls are not hooked up

[riastradh%NetBSD.org@localhost]

>Number:         50789
>Category:       kern
>Synopsis:       drmkms backlight/brightness controls are not hooked up
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Feb 10 01:30:00 +0000 2016
>Originator:     riastradh%NetBSD.org@localhost
>Release:        NetBSD-current
>Organization:
>Environment:
>Description:
>How-To-Repeat:

	All the backlight/brightness controls was never properly ported
	from the Linux backlight_device_register API.

>Fix:

	Either use pmf(9) to implement the backlight_device_register
	API and use the Linux code verbatim, or adapt the code
	explicitly.  There's a perhaps broken draft of the latter at
	<https://www.NetBSD.org/~riastradh/tmp/20160117/intel_brightness.patch>.