Comment 213 for bug 1098216

(In reply to comment #76)
> Created an attachment (id=99751) [details]
> Disable ACPI backlight for broken ThinkPads
>
> I'm attaching a new patch with a different take on this problem. It just
> disables the ACPI backlight control on these machines whenever the kernel has
> indicated Windows 8 compatibility via _OSI.
>
> Most machines should fall back to using a secondary backlight control, but
> it's
> possible that a few machines won't have another control. It's also likely
> that
> brightness changes on VTs using the hotkeys will be broken. In either of
> these
> cases it will be necessary to use acpi_osi="!Windows 2012", and I'd
> appreciate
> it if someone could test this case to verify the acpi_video backlight works
> as
> before with the new patch.
>
> Please give it a whirl and let me know your results. I've included quirks for
> every machine I'm aware of which is broken, but if I've missed any please let
> me know and include DMI information.
Patch works to regulate backlight, but xbacklight always return 0.
# tree /sys/class/backlight/
/sys/class/backlight/
|-- intel_backlight -> ../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight
`-- thinkpad_screen -> ../../devices/virtual/backlight/thinkpad_screen
# xbacklight
0.000000
# cat /sys/class/backlight/thinkpad_screen/max_brightness
7
# cat /sys/class/backlight/thinkpad_screen/brightness
0
But real backlight is 100%.