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- What: /sys/bus/usb/devices/.../power/autosuspend
- Date: March 2007
- KernelVersion: 2.6.21
- Contact: Alan Stern <stern@rowland.harvard.edu>
- Description:
- Each USB device directory will contain a file named
- power/autosuspend. This file holds the time (in seconds)
- the device must be idle before it will be autosuspended.
- 0 means the device will be autosuspended as soon as
- possible. Negative values will prevent the device from
- being autosuspended at all, and writing a negative value
- will resume the device if it is already suspended.
- The autosuspend delay for newly-created devices is set to
- the value of the usbcore.autosuspend module parameter.
- What: /sys/bus/usb/devices/.../power/level
- Date: March 2007
- KernelVersion: 2.6.21
- Contact: Alan Stern <stern@rowland.harvard.edu>
- Description:
- Each USB device directory will contain a file named
- power/level. This file holds a power-level setting for
- the device, one of "on", "auto", or "suspend".
- "on" means that the device is not allowed to autosuspend,
- although normal suspends for system sleep will still
- be honored. "auto" means the device will autosuspend
- and autoresume in the usual manner, according to the
- capabilities of its driver. "suspend" means the device
- is forced into a suspended state and it will not autoresume
- in response to I/O requests. However remote-wakeup requests
- from the device may still be enabled (the remote-wakeup
- setting is controlled separately by the power/wakeup
- attribute).
- During normal use, devices should be left in the "auto"
- level. The other levels are meant for administrative uses.
- If you want to suspend a device immediately but leave it
- free to wake up in response to I/O requests, you should
- write "0" to power/autosuspend.
- What: /sys/bus/usb/devices/.../power/persist
- Date: May 2007
- KernelVersion: 2.6.23
- Contact: Alan Stern <stern@rowland.harvard.edu>
- Description:
- If CONFIG_USB_PERSIST is set, then each USB device directory
- will contain a file named power/persist. The file holds a
- boolean value (0 or 1) indicating whether or not the
- "USB-Persist" facility is enabled for the device. Since the
- facility is inherently dangerous, it is disabled by default
- for all devices except hubs. For more information, see
- Documentation/usb/persist.txt.
- What: /sys/bus/usb/device/.../power/connected_duration
- Date: January 2008
- KernelVersion: 2.6.25
- Contact: Sarah Sharp <sarah.a.sharp@intel.com>
- Description:
- If CONFIG_PM and CONFIG_USB_SUSPEND are enabled, then this file
- is present. When read, it returns the total time (in msec)
- that the USB device has been connected to the machine. This
- file is read-only.
- Users:
- PowerTOP <power@bughost.org>
- http://www.lesswatts.org/projects/powertop/
- What: /sys/bus/usb/device/.../power/active_duration
- Date: January 2008
- KernelVersion: 2.6.25
- Contact: Sarah Sharp <sarah.a.sharp@intel.com>
- Description:
- If CONFIG_PM and CONFIG_USB_SUSPEND are enabled, then this file
- is present. When read, it returns the total time (in msec)
- that the USB device has been active, i.e. not in a suspended
- state. This file is read-only.
- Tools can use this file and the connected_duration file to
- compute the percentage of time that a device has been active.
- For example,
- echo $((100 * `cat active_duration` / `cat connected_duration`))
- will give an integer percentage. Note that this does not
- account for counter wrap.
- Users:
- PowerTOP <power@bughost.org>
- http://www.lesswatts.org/projects/powertop/
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