[Bug 207086] LCD Brightness

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=207086

            Bug ID: 207086
           Summary: LCD Brightness
           Product: Base System
           Version: 10.2-STABLE
          Hardware: amd64
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: freebsd-bugs at FreeBSD.org
          Reporter: aeuii at posteo.de
                CC: freebsd-amd64 at FreeBSD.org
                CC: freebsd-amd64 at FreeBSD.org

I'm unable to change LCD brightness on Lenovo Thinkpad Edge E145 using ☼+ and
☼- buttons. To be more specific, the brightness can be changed only until an
early system boot.  It works in the loader menu, and right after kernel is
loaded, but stops working soon after that (perhaps when acpi0 is loaded:
“acpi0: <LENOVO TP-HS> on motherboard”).

I tested multiple FreeBSD version:

Affected FreeBSD versions:
  - 11.0: FreeBSD-11.0-CURRENT-amd64-20160206-r295345-memstick.img
  - 10.3: FreeBSD-10.3-PRERELEASE-amd64-20160127-r294913-memstick.img
  - 10.2: 10.2-RELEASE-p12
  - 10.1: FreeBSD-10.1-RELEASE-amd64-memstick.img

Working version:
  - 9.3: FreeBSD-9.3-RELEASE-amd64-memstick.img (with “CPU0: local
    ACPI error 0x80”)

As you can see, the problem occurred between 9.3 and 10.1.


I also tried different methods to change the brightness on 10.2:

acpi_call
=========

acpi_call -v -p '\VBRU'

Path: \VBRU
Number of arguments: 0
ioctl: Device not configured

# no effect


acpi_ibm
========

sysctl dev.acpi_ibm.0.lcd_brightness=7

# value changes, but it no effect on the brightness


acpi_video
==========

sysctl hw.acpi.video.lcd0.brightness=50
hw.acpi.video.lcd0.brightness: 50 -> #

# no effect

pressing Fn+☼+- buttons has no effect, but logs:

can't evaluate \134_SB_.PCI0.VGA_.LCD_._BQC - AE_NOT_FOUND

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