1 What: /sys/bus/usb/devices/.../power 1 What: /sys/bus/usb/devices/.../power/level
2 Date: March 2007 2 Date: March 2007
3 KernelVersion: 2.6.21 3 KernelVersion: 2.6.21
4 Contact: Alan Stern <stern@rowland.harva 4 Contact: Alan Stern <stern@rowland.harvard.edu>
5 Description: 5 Description:
6 Each USB device directory will 6 Each USB device directory will contain a file named
7 power/level. This file holds 7 power/level. This file holds a power-level setting for
8 the device, either "on" or "au 8 the device, either "on" or "auto".
9 9
10 "on" means that the device is 10 "on" means that the device is not allowed to autosuspend,
11 although normal suspends for s 11 although normal suspends for system sleep will still
12 be honored. "auto" means the 12 be honored. "auto" means the device will autosuspend
13 and autoresume in the usual ma 13 and autoresume in the usual manner, according to the
14 capabilities of its driver. 14 capabilities of its driver.
15 15
16 During normal use, devices sho 16 During normal use, devices should be left in the "auto"
17 level. The "on" level is mean 17 level. The "on" level is meant for administrative uses.
18 If you want to suspend a devic 18 If you want to suspend a device immediately but leave it
19 free to wake up in response to 19 free to wake up in response to I/O requests, you should
20 write "0" to power/autosuspend 20 write "0" to power/autosuspend.
21 21
22 Device not capable of proper s 22 Device not capable of proper suspend and resume should be
23 left in the "on" level. Altho 23 left in the "on" level. Although the USB spec requires
24 devices to support suspend/res 24 devices to support suspend/resume, many of them do not.
25 In fact so many don't that by 25 In fact so many don't that by default, the USB core
26 initializes all non-hub device 26 initializes all non-hub devices in the "on" level. Some
27 drivers may change this settin 27 drivers may change this setting when they are bound.
28 28
29 This file is deprecated and wi 29 This file is deprecated and will be removed after 2010.
30 Use the power/control file ins 30 Use the power/control file instead; it does exactly the
31 same thing. 31 same thing.
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.