USB: OHCI: make URB completions single-threaded

URBs for a particular endpoint should complete sequentially.  That is,
we shouldn't call the completion handler for one URB until the handler
for the previous URB has returned.

When the OHCI watchdog routine is added, there will be two paths for
completing URBs: interrupt handler and watchdog routine.  Their
activities have to be synchronized so that completions don't occur in
multiple threads concurrently.

For that purpose, this patch creates an ohci_work() routine which will
be responsible for calling process_done_list() and finish_unlinks(),
the two routines that detect when an URB is complete.  Everything will
funnel through ohci_work(), and it will be careful not to run in more
than one thread at a time.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/ohci-hcd.c

@@ -316,7 +316,7 @@ static int ohci_urb_dequeue(struct usb_hcd *hcd, struct urb *urb, int status)
 
 		if (ohci->rh_state != OHCI_RH_RUNNING) {
 			/* With HC dead, we can clean up right away */
-			finish_unlinks(ohci, 0);
+			ohci_work(ohci);
 		}
 	}
 	spin_unlock_irqrestore (&ohci->lock, flags);
@@ -349,7 +349,7 @@ ohci_endpoint_disable (struct usb_hcd *hcd, struct usb_host_endpoint *ep)
 	if (ohci->rh_state != OHCI_RH_RUNNING) {
 sanitize:
 		ed->state = ED_IDLE;
-		finish_unlinks (ohci, 0);
+		ohci_work(ohci);
 	}
 
 	switch (ed->state) {
@@ -789,9 +789,7 @@ static irqreturn_t ohci_irq (struct usb_hcd *hcd)
 	/* handle any pending URB/ED unlinks, leaving INTR_SF enabled
 	 * when there's still unlinking to be done (next frame).
 	 */
-	process_done_list(ohci);
-	if (ohci->ed_rm_list)
-		finish_unlinks (ohci, ohci_frame_no(ohci));
+	ohci_work(ohci);
 	if ((ints & OHCI_INTR_SF) != 0 && !ohci->ed_rm_list
 			&& ohci->rh_state == OHCI_RH_RUNNING)
 		ohci_writel (ohci, OHCI_INTR_SF, &regs->intrdisable);
@@ -879,7 +877,7 @@ int ohci_restart(struct ohci_hcd *ohci)
 		if (!urb->unlinked)
 			urb->unlinked = -ESHUTDOWN;
 	}
-	finish_unlinks (ohci, 0);
+	ohci_work(ohci);
 	spin_unlock_irq(&ohci->lock);
 
 	/* paranoia, in case that didn't work: */

drivers/usb/host/ohci-hub.c

@@ -40,8 +40,7 @@
 	(OHCI_CTRL_CLE|OHCI_CTRL_BLE|OHCI_CTRL_PLE|OHCI_CTRL_IE)
 
 static void update_done_list(struct ohci_hcd *);
-static void process_done_list(struct ohci_hcd *);
-static void finish_unlinks (struct ohci_hcd *, u16);
+static void ohci_work(struct ohci_hcd *);
 
 #ifdef	CONFIG_PM
 static int ohci_rh_suspend (struct ohci_hcd *ohci, int autostop)
@@ -89,8 +88,7 @@ __acquires(ohci->lock)
 		spin_lock_irq (&ohci->lock);
 	}
 	update_done_list(ohci);
-	process_done_list(ohci);
-	finish_unlinks (ohci, ohci_frame_no(ohci));
+	ohci_work(ohci);
 
 	/*
 	 * Some controllers don't handle "global" suspend properly if

drivers/usb/host/ohci-q.c

@@ -964,9 +964,9 @@ static void update_done_list(struct ohci_hcd *ohci)
 /*-------------------------------------------------------------------------*/
 
 /* there are some urbs/eds to unlink; called in_irq(), with HCD locked */
-static void
-finish_unlinks (struct ohci_hcd *ohci, u16 tick)
+static void finish_unlinks(struct ohci_hcd *ohci)
 {
+	unsigned	tick = ohci_frame_no(ohci);
 	struct ed	*ed, **last;
 
 rescan_all:
@@ -1202,3 +1202,27 @@ static void process_done_list(struct ohci_hcd *ohci)
 		takeback_td(ohci, td);
 	}
 }
+
+/*
+ * TD takeback and URB giveback must be single-threaded.
+ * This routine takes care of it all.
+ */
+static void ohci_work(struct ohci_hcd *ohci)
+{
+	if (ohci->working) {
+		ohci->restart_work = 1;
+		return;
+	}
+	ohci->working = 1;
+
+ restart:
+	process_done_list(ohci);
+	if (ohci->ed_rm_list)
+		finish_unlinks(ohci);
+
+	if (ohci->restart_work) {
+		ohci->restart_work = 0;
+		goto restart;
+	}
+	ohci->working = 0;
+}

drivers/usb/host/ohci.h

@@ -393,6 +393,8 @@ struct ohci_hcd {
 	unsigned long		next_statechange;	/* suspend/resume */
 	u32			fminterval;		/* saved register */
 	unsigned		autostop:1;	/* rh auto stopping/stopped */
+	unsigned		working:1;
+	unsigned		restart_work:1;
 
 	unsigned long		flags;		/* for HC bugs */
 #define	OHCI_QUIRK_AMD756	0x01			/* erratum #4 */