USB: visor driver adapted to new tty buffering

the new tty buffering code allows usb drivers to stop private buffering.
In fact we must do so to allow flushing to work correctly. This does so
for the visor driver.
Signed-off-by: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/serial/visor.c

@@ -273,7 +273,8 @@ struct visor_private {
 	int bytes_in;
 	int bytes_out;
 	int outstanding_urbs;
-	int throttled;
+	unsigned char throttled;
+	unsigned char actually_throttled;
 };
 
 /* number of outstanding urbs to prevent userspace DoS from happening */
@@ -509,9 +510,8 @@ static void visor_read_bulk_callback (struct urb *urb)
 	struct visor_private *priv = usb_get_serial_port_data(port);
 	unsigned char *data = urb->transfer_buffer;
 	struct tty_struct *tty;
-	unsigned long flags;
-	int throttled;
 	int result;
+	int available_room;
 
 	dbg("%s - port %d", __FUNCTION__, port->number);
 
@@ -524,17 +524,20 @@ static void visor_read_bulk_callback (struct urb *urb)
 
 	tty = port->tty;
 	if (tty && urb->actual_length) {
-		tty_buffer_request_room(tty, urb->actual_length);
-		tty_insert_flip_string(tty, data, urb->actual_length);
+		available_room = tty_buffer_request_room(tty, urb->actual_length);
+		if (available_room) {
+			tty_insert_flip_string(tty, data, available_room);
 			tty_flip_buffer_push(tty);
 		}
-	spin_lock_irqsave(&priv->lock, flags);
-	priv->bytes_in += urb->actual_length;
-	throttled = priv->throttled;
-	spin_unlock_irqrestore(&priv->lock, flags);
+		spin_lock(&priv->lock);
+		priv->bytes_in += available_room;
+
+	} else {
+		spin_lock(&priv->lock);
+	}
 
 	/* Continue trying to always read if we should */
-	if (!throttled) {
+	if (!priv->throttled) {
 		usb_fill_bulk_urb (port->read_urb, port->serial->dev,
 				   usb_rcvbulkpipe(port->serial->dev,
 						   port->bulk_in_endpointAddress),
@@ -544,8 +547,10 @@ static void visor_read_bulk_callback (struct urb *urb)
 		result = usb_submit_urb(port->read_urb, GFP_ATOMIC);
 		if (result)
 			dev_err(&port->dev, "%s - failed resubmitting read urb, error %d\n", __FUNCTION__, result);
+	} else {
+		priv->actually_throttled = 1;
 	}
-	return;
+	spin_unlock(&priv->lock);
 }
 
 static void visor_read_int_callback (struct urb *urb)
@@ -608,6 +613,7 @@ static void visor_unthrottle (struct usb_serial_port *port)
 	dbg("%s - port %d", __FUNCTION__, port->number);
 	spin_lock_irqsave(&priv->lock, flags);
 	priv->throttled = 0;
+	priv->actually_throttled = 0;
 	spin_unlock_irqrestore(&priv->lock, flags);
 
 	port->read_urb->dev = port->serial->dev;