| Alan Stern | a903098 | 2010-04-02 13:22:16 -0400 | [diff] [blame] | 1 | What: /sys/bus/usb/devices/.../power/level |
| 2 | Date: March 2007 |
| 3 | KernelVersion: 2.6.21 |
| 4 | Contact: Alan Stern <stern@rowland.harvard.edu> |
| 5 | Description: |
| 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. |