brightness control on thinkpad t61p

[Andrew Morton <akpm@linux-foundation.org>]

When I fire up the latest Linus tree on my thinkpad t61p I get:

thinkpad_acpi: ThinkPad ACPI Extras v0.17
thinkpad_acpi: http://ibm-acpi.sf.net/
thinkpad_acpi: ThinkPad BIOS 7LET44WW (1.14 ), EC 7KHT22WW-1.06
thinkpad_acpi: Lenovo ThinkPad T61p
thinkpad_acpi: radio switch found; radios are enabled
ACPI: Lid Switch [LID]
input: Sleep Button (CM) as /class/input/input6
ACPI: Sleep Button (CM) [SLPB]
thinkpad_acpi: standard ACPI backlight interface available, not loading native one...



and /sys/class/backlight/thinkpad_screen/brightness is no longer present, so
my `brightness' script no longer works.  That, my friends, is a regression.

Here's my script:

(
0 sh -c "echo $1 > /proc/acpi/sony/brightness"
0 sh -c "echo $1 > /proc/acpi/sony/brightness_default"
0 sh -c "echo $1 > /sys/class/backlight/sony/brightness"
0 sh -c "echo $1 > /sys/class/backlight/thinkpad_screen/brightness"
) 2>/dev/null

which rather shows how pathetic we are in this area.  Ho hum.


So I go hunting around and find

	/sys/class/backlight/acpi_video0/
and
	/sys/class/backlight/acpi_video1/

Why are there two of them?


Both of these have a `brightness' entry which has contents of 100.  When I set
that to 10, the screen's brightness is not reduced.

So as far as I can tell, we have lost the ability to alter the brightness of
the screen on this machine.