drm2 regression: backlight adjustment on ivybridge no longer works

[Andrew Wilcox]

Ranjan1018 . sent: 26 January 2015 06:19:
> 2015-01-24 23:25 GMT+01:00 Adrian Chadd <adrian at freebsd.org>:
> > The backlight adjustment doesn't work on my ivybridge mobile laptop 
> > (Lenovo X230) after the dri update.
> >
> I have the same issue on my Samsung Ativ 2 laptop.

I have a Sandy Bridge laptop (Apple MacBook Pro 8,2) - HD 3000:

vgapci0 at pci0:0:2:0:     class=0x030000 card=0x00db106b chip=0x01268086 rev=0x09 hdr=0x00
    vendor     = 'Intel Corporation'
    device     = '2nd Generation Core Processor Family Integrated Graphics Controller'
    class      = display
    subclass   = VGA

It is running:  FreeBSD pwyll.foxkit.us 11.0-CURRENT #1 r277781M: Mon Jan 26 18:41:15 CST 2015 root at pwyll.foxkit.us:/usr/obj/usr/src/sys/GENERIC amd64

I have no issues using acpi_video's sysctls (hw.acpi.video.lcd0.brightness) to adjust backlight, though it does not have good granularity.  The stepping is about 7, so it goes as 13%..20%..27%..35%..etc.

> > The "intel_backlight" program from intel-gpu-tools" also no longer 
> > changes the backlight value.

This program works fine for me on both an older kernel (r277523) and this kernel (r277781), after applying some patches to allow the library to build on FreeBSD.  It also has better granularity (the stepping is 2-3).

If there is anything I can do/run to aide in debugging why it works for me but not others, let me know.

Best,
Andrew
--
Andrew Wilcox, C/C++/Python developer, kernel hacker
Blog:   http://blog.foxkit.us/  WWW: http://foxkit.us/ 
GitHub:  https://github.com/awilfox