linux/Documentation/ABI/obsolete/sysfs-bus-usb
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   1What:           /sys/bus/usb/devices/.../power/level
   2Date:           March 2007
   3KernelVersion:  2.6.21
   4Contact:        Alan Stern <stern@rowland.harvard.edu>
   5Description:
   6                Each USB device directory will contain a file named
   7                power/level.  This file holds a power-level setting for
   8                the device, either "on" or "auto".
   9
  10                "on" means that the device is not allowed to autosuspend,
  11                although normal suspends for system sleep will still
  12                be honored.  "auto" means the device will autosuspend
  13                and autoresume in the usual manner, according to the
  14                capabilities of its driver.
  15
  16                During normal use, devices should be left in the "auto"
  17                level.  The "on" level is meant for administrative uses.
  18                If you want to suspend a device immediately but leave it
  19                free to wake up in response to I/O requests, you should
  20                write "0" to power/autosuspend.
  21
  22                Device not capable of proper suspend and resume should be
  23                left in the "on" level.  Although the USB spec requires
  24                devices to support suspend/resume, many of them do not.
  25                In fact so many don't that by default, the USB core
  26                initializes all non-hub devices in the "on" level.  Some
  27                drivers may change this setting when they are bound.
  28
  29                This file is deprecated and will be removed after 2010.
  30                Use the power/control file instead; it does exactly the
  31                same thing.
  32
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