1*4882a593SmuzhiyunWhat: /sys/bus/usb/devices/.../power/level 2*4882a593SmuzhiyunDate: March 2007 3*4882a593SmuzhiyunKernelVersion: 2.6.21 4*4882a593SmuzhiyunContact: Alan Stern <stern@rowland.harvard.edu> 5*4882a593SmuzhiyunDescription: 6*4882a593Smuzhiyun Each USB device directory will contain a file named 7*4882a593Smuzhiyun power/level. This file holds a power-level setting for 8*4882a593Smuzhiyun the device, either "on" or "auto". 9*4882a593Smuzhiyun 10*4882a593Smuzhiyun "on" means that the device is not allowed to autosuspend, 11*4882a593Smuzhiyun although normal suspends for system sleep will still 12*4882a593Smuzhiyun be honored. "auto" means the device will autosuspend 13*4882a593Smuzhiyun and autoresume in the usual manner, according to the 14*4882a593Smuzhiyun capabilities of its driver. 15*4882a593Smuzhiyun 16*4882a593Smuzhiyun During normal use, devices should be left in the "auto" 17*4882a593Smuzhiyun level. The "on" level is meant for administrative uses. 18*4882a593Smuzhiyun If you want to suspend a device immediately but leave it 19*4882a593Smuzhiyun free to wake up in response to I/O requests, you should 20*4882a593Smuzhiyun write "0" to power/autosuspend. 21*4882a593Smuzhiyun 22*4882a593Smuzhiyun Device not capable of proper suspend and resume should be 23*4882a593Smuzhiyun left in the "on" level. Although the USB spec requires 24*4882a593Smuzhiyun devices to support suspend/resume, many of them do not. 25*4882a593Smuzhiyun In fact so many don't that by default, the USB core 26*4882a593Smuzhiyun initializes all non-hub devices in the "on" level. Some 27*4882a593Smuzhiyun drivers may change this setting when they are bound. 28*4882a593Smuzhiyun 29*4882a593Smuzhiyun This file is deprecated and will be removed after 2010. 30*4882a593Smuzhiyun Use the power/control file instead; it does exactly the 31*4882a593Smuzhiyun same thing. 32