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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/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/device/.../power/connected_duration
Date: January 2008
KernelVersion: 2.6.25
Contact: Sarah Sharp <sarah.a.sharp@intel.com>
Description:
If CONFIG_PM_RUNTIME is 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_RUNTIME is 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/
What: /sys/bus/usb/devices/<busnum>-<port[.port]>...:<config num>-<interface num>/supports_autosuspend
Date: January 2008
KernelVersion: 2.6.27
Contact: Sarah Sharp <sarah.a.sharp@intel.com>
Description:
When read, this file returns 1 if the interface driver
for this interface supports autosuspend. It also
returns 1 if no driver has claimed this interface, as an
unclaimed interface will not stop the device from being
autosuspended if all other interface drivers are idle.
The file returns 0 if autosuspend support has not been
added to the driver.
Users:
USB PM tool
git://git.moblin.org/users/sarah/usb-pm-tool/
What: /sys/bus/usb/device/.../avoid_reset_quirk
Date: December 2009
Contact: Oliver Neukum <oliver@neukum.org>
Description:
Writing 1 to this file tells the kernel that this
device will morph into another mode when it is reset.
Drivers will not use reset for error handling for
such devices.
Users:
usb_modeswitch
What: /sys/bus/usb/devices/.../devnum
KernelVersion: since at least 2.6.18
Description:
Device address on the USB bus.
What: /sys/bus/usb/devices/.../bConfigurationValue
KernelVersion: since at least 2.6.18
Description:
bConfigurationValue of the *active* configuration for the
device. Writing 0 or -1 to bConfigurationValue will reset the
active configuration (unconfigure the device). Writing
another value will change the active configuration.
Note that some devices, in violation of the USB spec, have a
configuration with a value equal to 0. Writing 0 to
bConfigurationValue for these devices will install that
configuration, rather then unconfigure the device.
Writing -1 will always unconfigure the device.
What: /sys/bus/usb/devices/.../busnum
KernelVersion: 2.6.22
Description:
Bus-number of the USB-bus the device is connected to.
What: /sys/bus/usb/devices/.../descriptors
KernelVersion: 2.6.26
Description:
Binary file containing cached descriptors of the device. The
binary data consists of the device descriptor followed by the
descriptors for each configuration of the device.
Note that the wTotalLength of the config descriptors can not
be trusted, as the device may have a smaller config descriptor
than it advertises. The bLength field of each (sub) descriptor
can be trusted, and can be used to seek forward one (sub)
descriptor at a time until the next config descriptor is found.
All descriptors read from this file are in bus-endian format
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