staging: comedi: usbdux: fix usbdux_counter_read()

Comedi (*insn_read) operations are supposed to read and return insn->n
values. Fix this function to work like the core expects.

Rename the local variable used for the private data pointer to the
comedi "norm".

Remove the unnecessary sanity check of the private data pointer. This
function can only be called is the private data was allocated during
the attach.

Tidy up the exit path using goto to ensure that the semaphore is
released.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/usbdux.c

@@ -1338,34 +1338,33 @@ static int usbdux_dio_insn_bits(struct comedi_device *dev,
 	return ret ? ret : insn->n;
 }
 
-/* reads the 4 counters, only two are used just now */
 static int usbdux_counter_read(struct comedi_device *dev,
 			       struct comedi_subdevice *s,
-			       struct comedi_insn *insn, unsigned int *data)
+			       struct comedi_insn *insn,
+			       unsigned int *data)
 {
-	struct usbdux_private *this_usbduxsub = dev->private;
-	int chan = insn->chanspec;
-	int err;
+	struct usbdux_private *devpriv = dev->private;
+	unsigned int chan = CR_CHAN(insn->chanspec);
+	int ret = 0;
+	int i;
 
-	if (!this_usbduxsub)
-		return -EFAULT;
+	down(&devpriv->sem);
 
-	down(&this_usbduxsub->sem);
-	err = send_dux_commands(dev, READCOUNTERCOMMAND);
-	if (err < 0) {
-		up(&this_usbduxsub->sem);
-		return err;
-	}
+	for (i = 0; i < insn->n; i++) {
+		ret = send_dux_commands(dev, READCOUNTERCOMMAND);
+		if (ret < 0)
+			goto counter_read_exit;
+		ret = receive_dux_commands(dev, READCOUNTERCOMMAND);
+		if (ret < 0)
+			goto counter_read_exit;
 
-	err = receive_dux_commands(dev, READCOUNTERCOMMAND);
-	if (err < 0) {
-		up(&this_usbduxsub->sem);
-		return err;
+		data[i] = le16_to_cpu(devpriv->insn_buffer[chan + 1]);
 	}
 
-	data[0] = le16_to_cpu(this_usbduxsub->insn_buffer[chan + 1]);
-	up(&this_usbduxsub->sem);
-	return 1;
+counter_read_exit:
+	up(&devpriv->sem);
+
+	return ret ? ret : insn->n;
 }
 
 static int usbdux_counter_write(struct comedi_device *dev,