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- 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.
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