[wellylug] usb behavior

E Chalaron filmtransfer.ec at gmail.com
Wed Apr 2 14:59:40 NZDT 2014

nope not UEFI, thanks. Unless I have it wrong I am not too familiar with 
this Uefi stuff.

However I think I am on something here... that's an old "todo" but seems 
to be consistent with my observation

    USB power management

A feature not yet implemented is USB power management. This is currently 
work in progress. With this feature, active USB devices are 
automatically deactivated when not used. A good example where this makes 
sense might be a web cam. However, this cannot be set on all systems and 
all devices automatically. A whitelist is needed, which makes the 
implementation a no-one-liner.

For activating it, userspace can write to the sysfs files in 
/sys/bus/usb/devices/*/power/level for each individual USB device like 

for dev in /sys/bus/usb/devices/*/power/level; do
         echo auto > $dev

This can save up to about 2 W, depending on the hardware in use. You can 
enable laptop-mode-tools to control this by editing 

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