staging:iio:buffer: pull computation of scan length into a utility function.

Principal reason is to make later patches more coherent and easier to review
but this set in itself separates a logical entity out nicely wihin the code.
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
Acked-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/iio/industrialio-buffer.c

@@ -508,29 +508,41 @@ static const unsigned long *iio_scan_mask_match(const unsigned long *av_masks,
 	return NULL;
 }
 
-int iio_sw_buffer_preenable(struct iio_dev *indio_dev)
+static int iio_compute_scan_bytes(struct iio_dev *indio_dev, const long *mask,
+				  bool timestamp)
 {
-	struct iio_buffer *buffer = indio_dev->buffer;
 	const struct iio_chan_spec *ch;
 	unsigned bytes = 0;
 	int length, i;
-	dev_dbg(&indio_dev->dev, "%s\n", __func__);
 
 	/* How much space will the demuxed element take? */
-	for_each_set_bit(i, buffer->scan_mask,
+	for_each_set_bit(i, mask,
 			 indio_dev->masklength) {
 		ch = iio_find_channel_from_si(indio_dev, i);
-		length = ch->scan_type.storagebits/8;
+		length = ch->scan_type.storagebits / 8;
 		bytes = ALIGN(bytes, length);
 		bytes += length;
 	}
-	if (buffer->scan_timestamp) {
+	if (timestamp) {
 		ch = iio_find_channel_from_si(indio_dev,
-					      buffer->scan_index_timestamp);
-		length = ch->scan_type.storagebits/8;
+					      indio_dev
+					      ->buffer->scan_index_timestamp);
+		length = ch->scan_type.storagebits / 8;
 		bytes = ALIGN(bytes, length);
 		bytes += length;
 	}
+	return bytes;
+}
+
+int iio_sw_buffer_preenable(struct iio_dev *indio_dev)
+{
+	struct iio_buffer *buffer = indio_dev->buffer;
+	unsigned bytes;
+	dev_dbg(&indio_dev->dev, "%s\n", __func__);
+
+	/* How much space will the demuxed element take? */
+	bytes = iio_compute_scan_bytes(indio_dev, buffer->scan_mask,
+				       buffer->scan_timestamp);
 	buffer->access->set_bytes_per_datum(buffer, bytes);
 
 	/* What scan mask do we actually have ?*/