diff --git a/drivers/staging/comedi/drivers/ni_65xx.c b/drivers/staging/comedi/drivers/ni_65xx.c
index aba6fbbe340a..0f9185ebda66 100644
--- a/drivers/staging/comedi/drivers/ni_65xx.c
+++ b/drivers/staging/comedi/drivers/ni_65xx.c
@@ -296,16 +296,18 @@ struct ni_65xx_private {
 	void __iomem *mmio;
 };
 
-static void ni_65xx_disable_input_filters(struct comedi_device *dev)
+static unsigned int ni_65xx_num_ports(struct comedi_device *dev)
 {
 	const struct ni_65xx_board *board = comedi_board(dev);
-	struct ni_65xx_private *devpriv = dev->private;
-	unsigned num_ports;
-	int i;
 
-	num_ports = board->num_dio_ports +
-		    board->num_di_ports +
-		    board->num_do_ports;
+	return board->num_dio_ports + board->num_di_ports + board->num_do_ports;
+}
+
+static void ni_65xx_disable_input_filters(struct comedi_device *dev)
+{
+	struct ni_65xx_private *devpriv = dev->private;
+	unsigned int num_ports = ni_65xx_num_ports(dev);
+	int i;
 
 	/* disable input filtering on all ports */
 	for (i = 0; i < num_ports; ++i)