USB: EHCI: add software retry for transaction errors

This patch (as1204) adds a software retry mechanism to ehci-hcd.  It
gets invoked when the driver encounters transaction errors on an
asynchronous endpoint.  On many systems, hardware deficiencies cause
such errors to occur if one device is unplugged while the host is
communicating with another device.  With the patch, the failed
transactions are retried and generally succeed the second or third
time through.

This is based on code originally written by Koichiro Saito.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Tested by: Koichiro Saito <Saito.Koichiro@adniss.jp>
CC: David Brownell <david-b@pacbell.net>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/host/ehci.h

@@ -342,6 +342,9 @@ struct ehci_qh {
 #define	QH_STATE_UNLINK_WAIT	4		/* LINKED and on reclaim q */
 #define	QH_STATE_COMPLETING	5		/* don't touch token.HALT */
 
+	u8			xacterrs;	/* XactErr retry counter */
+#define	QH_XACTERR_MAX		32		/* XactErr retry limit */
+
 	/* periodic schedule info */
 	u8			usecs;		/* intr bandwidth */
 	u8			gap_uf;		/* uframes split/csplit gap */