xhci: always handle "Command Ring Stopped" events

BugLink: http://bugs.launchpad.net/bugs/1621113

commit 33be1265 upstream.

Fix "Command completion event does not match command" errors by always
handling the command ring stopped events.

The command ring stopped event is generated as a result of aborting
or stopping the command ring with a register write. It is not caused
by a command in the command queue, and thus won't have a matching command
in the comman list.

Solve it by handling the command ring stopped event before checking for a
matching command.

In most command time out cases we abort the command ring, and get
a command ring stopped event. The events command pointer will point at
the current command ring dequeue, which in most cases matches the timed
out command in the command list, and no error messages are seen.

If we instead get a command aborted event before the command ring stopped
event, the abort event will increse the command ring dequeue pointer, and
the following command ring stopped events command pointer will point at the
next, not yet queued command. This case triggered the error message
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>

drivers/usb/host/xhci-ring.c

@@ -1331,12 +1331,6 @@ static void handle_cmd_completion(struct xhci_hcd *xhci,
 
 	cmd = list_entry(xhci->cmd_list.next, struct xhci_command, cmd_list);
 
-	if (cmd->command_trb != xhci->cmd_ring->dequeue) {
-		xhci_err(xhci,
-			 "Command completion event does not match command\n");
-		return;
-	}
-
 	del_timer(&xhci->cmd_timer);
 
 	trace_xhci_cmd_completion(cmd_trb, (struct xhci_generic_trb *) event);
@@ -1348,6 +1342,13 @@ static void handle_cmd_completion(struct xhci_hcd *xhci,
 		xhci_handle_stopped_cmd_ring(xhci, cmd);
 		return;
 	}
+
+	if (cmd->command_trb != xhci->cmd_ring->dequeue) {
+		xhci_err(xhci,
+			 "Command completion event does not match command\n");
+		return;
+	}
+
 	/*
 	 * Host aborted the command ring, check if the current command was
 	 * supposed to be aborted, otherwise continue normally.