Partially revert "staging:iio:gyro:adxrs450 make more use of spi_read and spi_write."

This partially reverts commit cb4496876f03631eff913b3c608c964d48d61eb9. There is
no apparent reason why we should split a transaction which consists out of
multiple transfers into multiple transactions each having one transfer. While
this works it introduces a bunch of unnecessary context switch and additional
setup costs.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/staging/iio/gyro/adxrs450_core.c

@@ -34,8 +34,21 @@ static int adxrs450_spi_read_reg_16(struct iio_dev *indio_dev,
 				    u8 reg_address,
 				    u16 *val)
 {
+	struct spi_message msg;
 	struct adxrs450_state *st = iio_priv(indio_dev);
 	int ret;
+	struct spi_transfer xfers[] = {
+		{
+			.tx_buf = st->tx,
+			.bits_per_word = 8,
+			.len = 4,
+			.cs_change = 1,
+		}, {
+			.rx_buf = st->rx,
+			.bits_per_word = 8,
+			.len = 4,
+		},
+	};
 
 	mutex_lock(&st->buf_lock);
 	st->tx[0] = ADXRS450_READ_DATA | (reg_address >> 7);
@@ -46,13 +59,10 @@ static int adxrs450_spi_read_reg_16(struct iio_dev *indio_dev,
 	if (!(hweight32(be32_to_cpu(*(u32 *)st->tx)) & 1))
 		st->tx[3]  |= ADXRS450_P;
 
-	ret = spi_write(st->us, st->tx, 4);
-	if (ret) {
-		dev_err(&st->us->dev, "problem while reading 16 bit register 0x%02x\n",
-			reg_address);
-		goto error_ret;
-	}
-	ret = spi_read(st->us, st->rx, 4);
+	spi_message_init(&msg);
+	spi_message_add_tail(&xfers[0], &msg);
+	spi_message_add_tail(&xfers[1], &msg);
+	ret = spi_sync(st->us, &msg);
 	if (ret) {
 		dev_err(&st->us->dev, "problem while reading 16 bit register 0x%02x\n",
 				reg_address);
@@ -105,8 +115,21 @@ static int adxrs450_spi_write_reg_16(struct iio_dev *indio_dev,
  **/
 static int adxrs450_spi_sensor_data(struct iio_dev *indio_dev, s16 *val)
 {
+	struct spi_message msg;
 	struct adxrs450_state *st = iio_priv(indio_dev);
 	int ret;
+	struct spi_transfer xfers[] = {
+		{
+			.tx_buf = st->tx,
+			.bits_per_word = 8,
+			.len = 4,
+			.cs_change = 1,
+		}, {
+			.rx_buf = st->rx,
+			.bits_per_word = 8,
+			.len = 4,
+		},
+	};
 
 	mutex_lock(&st->buf_lock);
 	st->tx[0] = ADXRS450_SENSOR_DATA;
@@ -114,13 +137,10 @@ static int adxrs450_spi_sensor_data(struct iio_dev *indio_dev, s16 *val)
 	st->tx[2] = 0;
 	st->tx[3] = 0;
 
-	ret = spi_write(st->us, st->tx, 4);
-	if (ret) {
-		dev_err(&st->us->dev, "Problem while reading sensor data\n");
-		goto error_ret;
-	}
-
-	ret = spi_read(st->us, st->rx, 4);
+	spi_message_init(&msg);
+	spi_message_add_tail(&xfers[0], &msg);
+	spi_message_add_tail(&xfers[1], &msg);
+	ret = spi_sync(st->us, &msg);
 	if (ret) {
 		dev_err(&st->us->dev, "Problem while reading sensor data\n");
 		goto error_ret;