torvalds/linux

What:        /sys/bus/usb/devices/.../power/level
Date:        March 2007
KernelVersion:    2.6.21
Contact:    Alan Stern <stern@rowland.harvard.edu>
Description:
        Each USB device directory will contain a file named
        power/level.  This file holds a power-level setting for
        the device, either "on" or "auto".

        "on" means that the device is not allowed to autosuspend,
        although normal suspends for system sleep will still
        be honored.  "auto" means the device will autosuspend
        and autoresume in the usual manner, according to the
        capabilities of its driver.

        During normal use, devices should be left in the "auto"
        level.  The "on" level is meant for administrative uses.
        If you want to suspend a device immediately but leave it
        free to wake up in response to I/O requests, you should
        write "0" to power/autosuspend.

        Device not capable of proper suspend and resume should be
        left in the "on" level.  Although the USB spec requires
        devices to support suspend/resume, many of them do not.
        In fact so many don't that by default, the USB core
        initializes all non-hub devices in the "on" level.  Some
        drivers may change this setting when they are bound.

        This file is deprecated and will be removed after 2010.
        Use the power/control file instead; it does exactly the
        same thing.