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What: /sys/bus/usb/devices/.../power/autosuspend
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Date: March 2007
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KernelVersion: 2.6.21
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Contact: Alan Stern <stern@rowland.harvard.edu>
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Description:
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Each USB device directory will contain a file named
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power/autosuspend. This file holds the time (in seconds)
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the device must be idle before it will be autosuspended.
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0 means the device will be autosuspended as soon as
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possible. Negative values will prevent the device from
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being autosuspended at all, and writing a negative value
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will resume the device if it is already suspended.
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The autosuspend delay for newly-created devices is set to
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the value of the usbcore.autosuspend module parameter.
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What: /sys/bus/usb/devices/.../power/level
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Date: March 2007
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KernelVersion: 2.6.21
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Contact: Alan Stern <stern@rowland.harvard.edu>
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Description:
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Each USB device directory will contain a file named
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power/level. This file holds a power-level setting for
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the device, one of "on", "auto", or "suspend".
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"on" means that the device is not allowed to autosuspend,
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although normal suspends for system sleep will still
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be honored. "auto" means the device will autosuspend
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and autoresume in the usual manner, according to the
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capabilities of its driver. "suspend" means the device
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is forced into a suspended state and it will not autoresume
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in response to I/O requests. However remote-wakeup requests
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from the device may still be enabled (the remote-wakeup
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setting is controlled separately by the power/wakeup
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attribute).
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During normal use, devices should be left in the "auto"
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level. The other levels are meant for administrative uses.
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If you want to suspend a device immediately but leave it
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free to wake up in response to I/O requests, you should
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write "0" to power/autosuspend.
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What: /sys/bus/usb/devices/.../power/persist
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Date: May 2007
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KernelVersion: 2.6.23
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Contact: Alan Stern <stern@rowland.harvard.edu>
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Description:
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If CONFIG_USB_PERSIST is set, then each USB device directory
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will contain a file named power/persist. The file holds a
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boolean value (0 or 1) indicating whether or not the
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"USB-Persist" facility is enabled for the device. Since the
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facility is inherently dangerous, it is disabled by default
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for all devices except hubs. For more information, see
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Documentation/usb/persist.txt.
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