USB: add power/persist device attribute

This patch (as920) adds an extra level of protection to the
USB-Persist facility.  Now it will apply by default only to hubs; for
all other devices the user must enable it explicitly by setting the
power/persist device attribute.

The disconnect_all_children() routine in hub.c has been removed and
its code placed inline.  This is the way it was originally as part of
hub_pre_reset(); the revised usage in hub_reset_resume() is
sufficiently different that the code can no longer be shared.
Likewise, mark_children_for_reset() is now inline as part of
hub_reset_resume().  The end result looks much cleaner than before.

The sysfs interface is updated to add the new attribute file, and
there are corresponding documentation updates.

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

1 files changed, 13 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-bus-usb b/Documentation/ABI/testing/sysfs-bus-usb
index f9937add033d..9734577d1711 100644
--- a/Documentation/ABI/testing/sysfs-bus-usb
+++ b/Documentation/ABI/testing/sysfs-bus-usb
@@ -39,3 +39,16 @@ Description:
                 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.
+
+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.