18c2ecf20Sopenharmony_ciWhat: /sys/bus/usb/devices/.../power/level 28c2ecf20Sopenharmony_ciDate: March 2007 38c2ecf20Sopenharmony_ciKernelVersion: 2.6.21 48c2ecf20Sopenharmony_ciContact: Alan Stern <stern@rowland.harvard.edu> 58c2ecf20Sopenharmony_ciDescription: 68c2ecf20Sopenharmony_ci Each USB device directory will contain a file named 78c2ecf20Sopenharmony_ci power/level. This file holds a power-level setting for 88c2ecf20Sopenharmony_ci the device, either "on" or "auto". 98c2ecf20Sopenharmony_ci 108c2ecf20Sopenharmony_ci "on" means that the device is not allowed to autosuspend, 118c2ecf20Sopenharmony_ci although normal suspends for system sleep will still 128c2ecf20Sopenharmony_ci be honored. "auto" means the device will autosuspend 138c2ecf20Sopenharmony_ci and autoresume in the usual manner, according to the 148c2ecf20Sopenharmony_ci capabilities of its driver. 158c2ecf20Sopenharmony_ci 168c2ecf20Sopenharmony_ci During normal use, devices should be left in the "auto" 178c2ecf20Sopenharmony_ci level. The "on" level is meant for administrative uses. 188c2ecf20Sopenharmony_ci If you want to suspend a device immediately but leave it 198c2ecf20Sopenharmony_ci free to wake up in response to I/O requests, you should 208c2ecf20Sopenharmony_ci write "0" to power/autosuspend. 218c2ecf20Sopenharmony_ci 228c2ecf20Sopenharmony_ci Device not capable of proper suspend and resume should be 238c2ecf20Sopenharmony_ci left in the "on" level. Although the USB spec requires 248c2ecf20Sopenharmony_ci devices to support suspend/resume, many of them do not. 258c2ecf20Sopenharmony_ci In fact so many don't that by default, the USB core 268c2ecf20Sopenharmony_ci initializes all non-hub devices in the "on" level. Some 278c2ecf20Sopenharmony_ci drivers may change this setting when they are bound. 288c2ecf20Sopenharmony_ci 298c2ecf20Sopenharmony_ci This file is deprecated and will be removed after 2010. 308c2ecf20Sopenharmony_ci Use the power/control file instead; it does exactly the 318c2ecf20Sopenharmony_ci same thing. 32