staging:iio:adc:ad7298 use iio_sw_buffer_preenable to avoid code repitition.

Here some addition elements are needed, but this generic function cuts
down on the amount of 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/adc/ad7298.h

@@ -38,7 +38,6 @@ struct ad7298_platform_data {
 struct ad7298_state {
 	struct spi_device		*spi;
 	struct regulator		*reg;
-	size_t				d_size;
 	u16				int_vref_mv;
 	unsigned			ext_ref;
 	struct spi_transfer		ring_xfer[10];

drivers/staging/iio/adc/ad7298_ring.c

@@ -28,25 +28,17 @@
 static int ad7298_ring_preenable(struct iio_dev *indio_dev)
 {
 	struct ad7298_state *st = iio_priv(indio_dev);
-	struct iio_buffer *ring = indio_dev->buffer;
-	size_t d_size;
 	int i, m;
 	unsigned short command;
-	int scan_count = bitmap_weight(indio_dev->active_scan_mask,
-				       indio_dev->masklength);
-	d_size = scan_count * (AD7298_STORAGE_BITS / 8);
-
-	if (ring->scan_timestamp) {
-		d_size += sizeof(s64);
-
-		if (d_size % sizeof(s64))
-			d_size += sizeof(s64) - (d_size % sizeof(s64));
-	}
+	int scan_count, ret;
 
-	if (ring->access->set_bytes_per_datum)
-		ring->access->set_bytes_per_datum(ring, d_size);
+	ret = iio_sw_buffer_preenable(indio_dev);
+	if (ret < 0)
+		return ret;
 
-	st->d_size = d_size;
+	/* Now compute overall size */
+	scan_count = bitmap_weight(indio_dev->active_scan_mask,
+				   indio_dev->masklength);
 
 	command = AD7298_WRITE | st->ext_ref;
 
@@ -102,7 +94,7 @@ static irqreturn_t ad7298_trigger_handler(int irq, void *p)
 
 	if (ring->scan_timestamp) {
 		time_ns = iio_get_time_ns();
-		memcpy((u8 *)buf + st->d_size - sizeof(s64),
+		memcpy((u8 *)buf + indio_dev->scan_bytes - sizeof(s64),
 			&time_ns, sizeof(time_ns));
 	}