USB: add power/level sysfs attribute

This patch (as874) adds another piece to the user-visible part of the
USB autosuspend interface.  The new power/level sysfs attribute allows
users to force the device on (with autosuspend off), force the device
to sleep (with autoresume off), or return to normal automatic operation.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 26 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-bus-usb b/Documentation/ABI/testing/sysfs-bus-usb
index 00a84326325f..f9937add033d 100644
--- a/Documentation/ABI/testing/sysfs-bus-usb
+++ b/Documentation/ABI/testing/sysfs-bus-usb
@@ -13,3 +13,29 @@ Description:
 
                 The autosuspend delay for newly-created devices is set to
                 the value of the usbcore.autosuspend module parameter.
+
+What:           /sys/bus/usb/devices/.../power/level
+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/level.  This file holds a power-level setting for
+                the device, one of "on", "auto", or "suspend".
+
+                "on" means that the device is not allowed to autosuspend,
+                although normal suspends for system sleep will still
+                be honored.  "auto" means the device will autosuspend
+                and autoresume in the usual manner, according to the
+                capabilities of its driver.  "suspend" means the device
+                is forced into a suspended state and it will not autoresume
+                in response to I/O requests.  However remote-wakeup requests
+                from the device may still be enabled (the remote-wakeup
+                setting is controlled separately by the power/wakeup
+                attribute).
+
+                During normal use, devices should be left in the "auto"
+                level.  The other levels are meant for administrative uses.
+                If you want to suspend a device immediately but leave it
+                free to wake up in response to I/O requests, you should
+                write "0" to power/autosuspend.