USB: serial: continue to read on errors

Make sure to try to resubmit the read urb on errors.

Currently a recoverable error would lead to reduced throughput as only
one urb will be used until the port is closed and reopened (or
resumed or unthrottled).

Also upgrade error messages from debug to error log level.
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>

drivers/usb/serial/generic.c

@@ -359,16 +359,29 @@ void usb_serial_generic_read_bulk_callback(struct urb *urb)
 
 	dev_dbg(&port->dev, "%s - urb %d, len %d\n", __func__, i,
 							urb->actual_length);
-
-	if (urb->status) {
-		dev_dbg(&port->dev, "%s - non-zero urb status: %d\n",
-			__func__, urb->status);
+	switch (urb->status) {
+	case 0:
+		break;
+	case -ENOENT:
+	case -ECONNRESET:
+	case -ESHUTDOWN:
+		dev_dbg(&port->dev, "%s - urb stopped: %d\n",
+							__func__, urb->status);
+		return;
+	case -EPIPE:
+		dev_err(&port->dev, "%s - urb stopped: %d\n",
+							__func__, urb->status);
 		return;
+	default:
+		dev_err(&port->dev, "%s - nonzero urb status: %d\n",
+							__func__, urb->status);
+		goto resubmit;
 	}
 
 	usb_serial_debug_data(&port->dev, __func__, urb->actual_length, data);
 	port->serial->type->process_read_urb(urb);
 
+resubmit:
 	/* Throttle the device if requested by tty */
 	spin_lock_irqsave(&port->lock, flags);
 	port->throttled = port->throttle_req;