Commit | Line | Data |
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a9030986 AS |
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. |