USB: EHCI: fix regression during bus resume

This patch (as1663) fixes a regression caused by commit
6e0c3339a6f19d748f16091d0a05adeb1e1f822b (USB: EHCI: unlink one async
QH at a time).  In order to avoid keeping multiple QHs in an unusable
intermediate state, that commit changed unlink_empty_async() so that
it unlinks only one empty QH at a time.

However, when the EHCI root hub is suspended, _all_ async QHs need to
be unlinked.  ehci_bus_suspend() used to do this by calling
unlink_empty_async(), but now this only unlinks one of the QHs, not
all of them.

The symptom is that when the root hub is resumed, USB communications
don't work for some period of time.  This is because ehci-hcd doesn't
realize it needs to restart the async schedule; it assumes that
because some QHs are already on the schedule, the schedule must be
running.

The easiest way to fix the problem is add a new function that unlinks
all the async QHs when the root hub is suspended.

This patch should be applied to all kernels that have the 6e0c3339a6f1
commit.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-and-tested-by: Adrian Bassett <adrian.bassett@hotmail.co.uk>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/ehci-hcd.c

@@ -302,6 +302,7 @@ static void ehci_quiesce (struct ehci_hcd *ehci)
 
 static void end_unlink_async(struct ehci_hcd *ehci);
 static void unlink_empty_async(struct ehci_hcd *ehci);
+static void unlink_empty_async_suspended(struct ehci_hcd *ehci);
 static void ehci_work(struct ehci_hcd *ehci);
 static void start_unlink_intr(struct ehci_hcd *ehci, struct ehci_qh *qh);
 static void end_unlink_intr(struct ehci_hcd *ehci, struct ehci_qh *qh);

drivers/usb/host/ehci-hub.c

@@ -328,7 +328,7 @@ static int ehci_bus_suspend (struct usb_hcd *hcd)
 	ehci->rh_state = EHCI_RH_SUSPENDED;
 
 	end_unlink_async(ehci);
-	unlink_empty_async(ehci);
+	unlink_empty_async_suspended(ehci);
 	ehci_handle_intr_unlinks(ehci);
 	end_free_itds(ehci);
 

drivers/usb/host/ehci-q.c

@@ -1316,6 +1316,19 @@ static void unlink_empty_async(struct ehci_hcd *ehci)
 	}
 }
 
+/* The root hub is suspended; unlink all the async QHs */
+static void unlink_empty_async_suspended(struct ehci_hcd *ehci)
+{
+	struct ehci_qh		*qh;
+
+	while (ehci->async->qh_next.qh) {
+		qh = ehci->async->qh_next.qh;
+		WARN_ON(!list_empty(&qh->qtd_list));
+		single_unlink_async(ehci, qh);
+	}
+	start_iaa_cycle(ehci, false);
+}
+
 /* makes sure the async qh will become idle */
 /* caller must own ehci->lock */