[CFT] acpi_ibm event handler

[Mitsuru IWASAKI]

Hi,

> Brightness can be adjusted using "acpi_call -p '\VBRC' -i n" (where n
> is 0-15). acpi_call must be installed from ports. But this command
> sets absolute brightness, so it can't raise or lower the brightness
> unless you have the current value and I don't know how to get that.
> This is the case on my T520.

X61 has the same problem.  There are 2 video device object in ACPI
namespace, \_SB.PCI0.VID (vgapci attached but brightness control
doesn't work) and \_SB.PCI0.AGP.VID (has VBRC method but no driver
attached because of wrong _ADR).

The custom DSDT with the following patches and acpi_video(4) now
can adjust brightness level :)

http://people.freebsd.org/~iwasaki/acpi/tpx61.asl.diff

If you want to make the custom DSDT, I can help you.

Thanks!