| 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. |
