USB: Add documentation for USB suspend statistics.

This documents two newly created files:
/sys/bus/usb/device/.../power/connected_duration
/sys/bus/usb/device/.../power/active_duration

Documentation was placed in Documentation/ABI/testing, since that's where the
documentation is for the other USB sysfs power files.

Signed-off-by: Sarah Sharp <sarah.a.sharp@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/Documentation/ABI/testing/sysfs-bus-usb b/Documentation/ABI/testing/sysfs-bus-usb
index 9734577..11a3c16 100644 (file)
--- a/Documentation/ABI/testing/sysfs-bus-usb
+++ b/Documentation/ABI/testing/sysfs-bus-usb
@@ -52,3 +52,36 @@ Description:
                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/