| 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. |