USB: ehci: qh_completions cleanup and bugfix

Simplify processing of completed qtds, and correct handling of short
reads, by removing two state variables:

 - "qtd_status" wasn't needed.  The current URB's status is either
   OK (-EINPROGRESS) or some fault status.  Once a fault appears,
   the queue halts and any later QTDs are immediately removed, so
   no temporary status is needed.  (Or for typical short reads,
   it's not treated as a fault, so no queue halt is needed.)

 - "do_status" was erroneous.  Because of how the queue is set up,
   short control reads can (and should!) be treated like full size
   reads, and cleaned up the usual way.  The status stage will be
   executed transparently, and usbcore handles the choice of whether
   to report this status as unexected.
 
The "do_status" problem caused a rather perplexing timing-dependent
problem with usbtest case 10.  Sometimes it would make the controller
skip a dozen transactions while (wrongly) trying to clean up after a
short transfer.  Fortunately, removing a dcache contention issue made
this become trivial to reproduce (on one test rig), so enough clues
finally presented themselves ... I think this has been around for a
very long time, but was worsened by recent urb->status changes.
Signed-off-by: NDavid Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/usb/host/ehci-q.c

@@ -242,7 +242,8 @@ __acquires(ehci->lock)
 	if (unlikely(urb->unlinked)) {
 		COUNT(ehci->stats.unlink);
 	} else {
-		if (likely(status == -EINPROGRESS))
+		/* report non-error and short read status as zero */
+		if (status == -EINPROGRESS || status == -EREMOTEIO)
 			status = 0;
 		COUNT(ehci->stats.complete);
 	}
@@ -283,7 +284,6 @@ qh_completions (struct ehci_hcd *ehci, struct ehci_qh *qh)
 	int			last_status = -EINPROGRESS;
 	int			stopped;
 	unsigned		count = 0;
-	int			do_status = 0;
 	u8			state;
 	u32			halt = HALT_BIT(ehci);
 
@@ -309,7 +309,6 @@ qh_completions (struct ehci_hcd *ehci, struct ehci_qh *qh)
 		struct ehci_qtd	*qtd;
 		struct urb	*urb;
 		u32		token = 0;
-		int		qtd_status;
 
 		qtd = list_entry (entry, struct ehci_qtd, qtd_list);
 		urb = qtd->urb;
@@ -377,13 +376,6 @@ qh_completions (struct ehci_hcd *ehci, struct ehci_qh *qh)
 			else if (last_status == -EINPROGRESS && !urb->unlinked)
 				continue;
 
-			/* issue status after short control reads */
-			if (unlikely (do_status != 0)
-					&& QTD_PID (token) == 0 /* OUT */) {
-				do_status = 0;
-				continue;
-			}
-
 			/* qh unlinked; token in overlay may be most current */
 			if (state == QH_STATE_IDLE
 					&& cpu_to_hc32(ehci, qtd->qtd_dma)
@@ -401,15 +393,21 @@ qh_completions (struct ehci_hcd *ehci, struct ehci_qh *qh)
 			}
 		}
 
-		/* remove it from the queue */
-		qtd_status = qtd_copy_status(ehci, urb, qtd->length, token);
-		if (unlikely(qtd_status == -EREMOTEIO)) {
-			do_status = (!urb->unlinked &&
-					usb_pipecontrol(urb->pipe));
-			qtd_status = 0;
+		/* unless we already know the urb's status, collect qtd status
+		 * and update count of bytes transferred.  in common short read
+		 * cases with only one data qtd (including control transfers),
+		 * queue processing won't halt.  but with two or more qtds (for
+		 * example, with a 32 KB transfer), when the first qtd gets a
+		 * short read the second must be removed by hand.
+		 */
+		if (last_status == -EINPROGRESS) {
+			last_status = qtd_copy_status(ehci, urb,
+					qtd->length, token);
+			if (last_status == -EREMOTEIO
+					&& (qtd->hw_alt_next
+						& EHCI_LIST_END(ehci)))
+				last_status = -EINPROGRESS;
 		}
-		if (likely(last_status == -EINPROGRESS))
-			last_status = qtd_status;
 
 		/* if we're removing something not at the queue head,
 		 * patch the hardware queue pointer.