diff --git a/drivers/staging/comedi/drivers/ni_65xx.c b/drivers/staging/comedi/drivers/ni_65xx.c
index 3ba4c5712dffe5c9277bab3a0a59933e2b5a7c59..853f62b2b1a982c70ba229f94b4697c9d1e869d3 100644
--- a/drivers/staging/comedi/drivers/ni_65xx.c
+++ b/drivers/staging/comedi/drivers/ni_65xx.c
@@ -369,28 +369,23 @@ static int ni_65xx_dio_insn_bits(struct comedi_device *dev,
 {
 	const struct ni_65xx_board *board = comedi_board(dev);
 	struct ni_65xx_private *devpriv = dev->private;
-	unsigned base_bitfield_channel;
-	const unsigned max_ports_per_bitfield = 5;
+	int base_bitfield_channel;
 	unsigned read_bits = 0;
-	unsigned j;
+	int last_port_offset = ni_65xx_port_by_channel(s->n_chan - 1);
+	int port_offset;
 
 	base_bitfield_channel = CR_CHAN(insn->chanspec);
-	for (j = 0; j < max_ports_per_bitfield; ++j) {
-		const unsigned port_offset =
-			ni_65xx_port_by_channel(base_bitfield_channel) + j;
-		const unsigned port =
-			sprivate(s)->base_port + port_offset;
-		unsigned base_port_channel;
+	for (port_offset = ni_65xx_port_by_channel(base_bitfield_channel);
+	     port_offset <= last_port_offset; port_offset++) {
+		unsigned port = sprivate(s)->base_port + port_offset;
+		int base_port_channel = port_offset * ni_65xx_channels_per_port;
 		unsigned port_mask, port_data, port_read_bits;
-		int bitshift;
-		if (port >= ni_65xx_total_num_ports(board))
+		int bitshift = base_port_channel - base_bitfield_channel;
+
+		if (bitshift >= 32)
 			break;
-		base_port_channel = port_offset * ni_65xx_channels_per_port;
 		port_mask = data[0];
 		port_data = data[1];
-		bitshift = base_port_channel - base_bitfield_channel;
-		if (bitshift >= 32 || bitshift <= -32)
-			break;
 		if (bitshift > 0) {
 			port_mask >>= bitshift;
 			port_data >>= bitshift;