staging: comedi: usbduxfast: tidy up usbduxfast_ai_insn_read()

Remove the sanity check of devpriv, this function can only be called
by the comedi core if the private data is allocated.

Get the 'chan', 'range' and 'rngmask' from the function parameters
when the local variables are declared.

For aesthetic reasons, rename the local variable 'err' to 'ret'
since that name is more standard.

(*insn_read) functions are supposed to return the number of values
read or an error code. Change the final return to 'insn->n' to make
it clearer.
Signed-off-by: NH Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/usbduxfast.c

@@ -868,36 +868,28 @@ static int usbduxfast_ai_cmd(struct comedi_device *dev,
  */
 static int usbduxfast_ai_insn_read(struct comedi_device *dev,
 				   struct comedi_subdevice *s,
-				   struct comedi_insn *insn, unsigned int *data)
+				   struct comedi_insn *insn,
+				   unsigned int *data)
 {
 	struct usb_interface *intf = comedi_to_usb_interface(dev);
 	struct usb_device *usb = interface_to_usbdev(intf);
 	struct usbduxfast_private *devpriv = dev->private;
+	unsigned int chan = CR_CHAN(insn->chanspec);
+	unsigned int range = CR_RANGE(insn->chanspec);
+	uint8_t rngmask = range ? (0xff - 0x04) : 0xff;
 	int i, j, n, actual_length;
-	int chan, range, rngmask;
-	int err;
-
-	if (!devpriv) {
-		dev_err(dev->class_dev, "no usb dev\n");
-		return -ENODEV;
-	}
+	int ret;
 
 	down(&devpriv->sem);
+
 	if (devpriv->ai_cmd_running) {
 		dev_err(dev->class_dev,
 			"ai_insn_read not possible, async cmd is running\n");
 		up(&devpriv->sem);
 		return -EBUSY;
 	}
-	/* sample one channel */
-	chan = CR_CHAN(insn->chanspec);
-	range = CR_RANGE(insn->chanspec);
-	/* set command for the first channel */
 
-	if (range > 0)
-		rngmask = 0xff - 0x04;
-	else
-		rngmask = 0xff;
+	/* set command for the first channel */
 
 	/* commit data to the FIFO */
 	/* data */
@@ -913,32 +905,31 @@ static int usbduxfast_ai_insn_read(struct comedi_device *dev,
 	usbduxfast_cmd_data(dev, 5, 0x0c, 0x00, rngmask, 0x00);
 	usbduxfast_cmd_data(dev, 6, 0x01, 0x00, rngmask, 0x00);
 
-	/* 0 means that the AD commands are sent */
-	err = usbduxfast_send_cmd(dev, SENDADCOMMANDS);
-	if (err < 0) {
+	ret = usbduxfast_send_cmd(dev, SENDADCOMMANDS);
+	if (ret < 0) {
 		up(&devpriv->sem);
-		return err;
+		return ret;
 	}
 
 	for (i = 0; i < PACKETS_TO_IGNORE; i++) {
-		err = usb_bulk_msg(usb, usb_rcvbulkpipe(usb, BULKINEP),
+		ret = usb_bulk_msg(usb, usb_rcvbulkpipe(usb, BULKINEP),
 				   devpriv->inbuf, SIZEINBUF,
 				   &actual_length, 10000);
-		if (err < 0) {
+		if (ret < 0) {
 			dev_err(dev->class_dev, "insn timeout, no data\n");
 			up(&devpriv->sem);
-			return err;
+			return ret;
 		}
 	}
-	/* data points */
+
 	for (i = 0; i < insn->n;) {
-		err = usb_bulk_msg(usb, usb_rcvbulkpipe(usb, BULKINEP),
+		ret = usb_bulk_msg(usb, usb_rcvbulkpipe(usb, BULKINEP),
 				   devpriv->inbuf, SIZEINBUF,
 				   &actual_length, 10000);
-		if (err < 0) {
-			dev_err(dev->class_dev, "insn data error: %d\n", err);
+		if (ret < 0) {
+			dev_err(dev->class_dev, "insn data error: %d\n", ret);
 			up(&devpriv->sem);
-			return err;
+			return ret;
 		}
 		n = actual_length / sizeof(uint16_t);
 		if ((n % 16) != 0) {
@@ -951,8 +942,10 @@ static int usbduxfast_ai_insn_read(struct comedi_device *dev,
 			i++;
 		}
 	}
+
 	up(&devpriv->sem);
-	return i;
+
+	return insn->n;
 }
 
 static int usbduxfast_attach_common(struct comedi_device *dev)