[ltp] T400 does not enter C4/C6 sleep state with USB devices connected

[Richard Neill]

Henrique de Moraes Holschuh wrote:
> On Thu, 18 Feb 2010, Pedro Ribeiro wrote:
>> I spent lots of hours trying to figure out why my T400 would not enter
>> C4 and C6 sleep states.
>>
>> Here are my findings for anyone which is interested:
>> - When a USB device is connected, even if it supports USB autosuspend,
>> the cpu will never go down more than C3 (apparently the mode is
>> disabled by the BIOS).
>> - After removing all the USB devices, in AC it enters C4 and in
>> battery it enters C6.

On my X60, the following trick seems to work. Both are required, 
otherwise it rarely goes into the lowest C-state (on the X60, this means 
C3, rather than C2)

for i in /sys/bus/usb/devices/*/power/autosuspend; do echo 1 > $i ; done
for i in /sys/bus/usb/devices/*/power/level ; do echo auto > $i ; done

This is what powertop does when it prompts for 'U'.

Richard