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, either "on" or "auto".
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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.
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During normal use, devices should be left in the "auto"
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level. The "on" level is 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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Device not capable of proper suspend and resume should be
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left in the "on" level. Although the USB spec requires
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devices to support suspend/resume, many of them do not.
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In fact so many don't that by default, the USB core
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initializes all non-hub devices in the "on" level. Some
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drivers may change this setting when they are bound.
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This file is deprecated and will be removed after 2010.
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Use the power/control file instead; it does exactly the
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same thing.
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