USB: EHCI: use hrtimer for unlinking empty async QHs

This patch (as1583) changes ehci-hcd to use an hrtimer event for
unlinking empty (unused) async QHs instead of using a kernel timer.

The check for empty QHs is moved to a new routine, where it doesn't
require going through an entire scan of both the async and periodic
schedules.  And it can unlink multiple QHs at once, unlike the current
code.

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

drivers/usb/host/ehci.h

@@ -84,6 +84,7 @@ enum ehci_hrtimer_event {
 	EHCI_HRTIMER_POLL_DEAD,		/* Wait for dead controller to stop */
 	EHCI_HRTIMER_UNLINK_INTR,	/* Wait for interrupt QH unlink */
 	EHCI_HRTIMER_FREE_ITDS,		/* Wait for unused iTDs and siTDs */
+	EHCI_HRTIMER_ASYNC_UNLINKS,	/* Unlink empty async QHs */
 	EHCI_HRTIMER_IAA_WATCHDOG,	/* Handle lost IAA interrupts */
 	EHCI_HRTIMER_DISABLE_PERIODIC,	/* Wait to disable periodic sched */
 	EHCI_HRTIMER_DISABLE_ASYNC,	/* Wait to disable async sched */
@@ -123,6 +124,7 @@ struct ehci_hcd {			/* one per controller */
 	struct ehci_qh		*async_unlink_last;
 	struct ehci_qh		*async_iaa;
 	struct ehci_qh		*qh_scan_next;
+	unsigned		async_unlink_cycle;
 	unsigned		async_count;	/* async activity count */
 
 	/* periodic schedule support */
@@ -232,7 +234,6 @@ static inline struct usb_hcd *ehci_to_hcd (struct ehci_hcd *ehci)
 
 enum ehci_timer_action {
 	TIMER_IO_WATCHDOG,
-	TIMER_ASYNC_SHRINK,
 };
 
 static inline void
@@ -382,7 +383,6 @@ struct ehci_qh {
 	struct ehci_qtd		*dummy;
 	struct ehci_qh		*unlink_next;	/* next on unlink list */
 
-	unsigned long		unlink_time;
 	unsigned		unlink_cycle;
 	unsigned		stamp;