Problem with LCD backlight remaining on during ACPI sleep

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Problem description

On some models the LCD backlight remains on during ACPI sleep. This apparently affects various models (the T30, X31, A31p are mentioned on the relevant bug on the Kernel bug tracker (bug 2576).

Partial solution

If the ThinkPad has a radeon video chip, then switching off the light with the command 

 radeontool light off

will work, but only in a text-mode virtual terminal. If X is running, the light apparently comes back on when the kernel switches to text mode prior to sleeping. The solution in that case it to switch to a text mode console first.

I use the following script to suspend my machine. The hwclock lines compensate for the clock running at double speed during suspend (weird!). 

logger "Software suspend to ram."
sync
/sbin/hwclock --systohc
chvt 1
radeontool light off
echo -n 3 >/proc/acpi/sleep
/sbin/hwclock --adjust
/sbin/hwclock --hctosys
logger "Woke up from suspend."
radeontool light on
chvt 7

Improvements are clearly possible. :-)

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