USB: keep count of unsuspended children

This patch (as818b) simplifies autosuspend processing by keeping track
of the number of unsuspended children of each USB hub.  This will
permit us to avoid a good deal of unnecessary work all the time; we
will no longer have to create a bunch of workqueue entries to carry
out autosuspend requests, only to have them fail because one of the
hub's children isn't suspended.

The basic idea is simple.  There already is a usage counter in the
usb_device structure for preventing autosuspends.  The patch just
increments that counter for every unsuspended child.  There's only one
tricky part: When a device disconnects we need to remember whether it
was suspended at the time (leave the counter alone) or not (decrement
the counter).

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

include/linux/usb.h

@@ -362,6 +362,7 @@ struct usb_device {
 	u8 portnum;			/* Parent port number (origin 1) */
 	u8 level;			/* Number of USB hub ancestors */
 
+	unsigned discon_suspended:1;	/* Disconnected while suspended */
 	unsigned have_langid:1;		/* whether string_langid is valid */
 	int string_langid;		/* language ID for strings */