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>

1 files changed, 33 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-bus-usb b/Documentation/ABI/testing/sysfs-bus-usb
index 9734577d1711..11a3c1682cec 100644
--- 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/