iio:ad5504: Do not store transfer buffers on the stack

Some SPI controllers may not be able to handle transfer buffers that are placed
on the stack.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/dac/ad5504.c

@@ -47,14 +47,16 @@
  * @vref_mv:		actual reference voltage used
  * @pwr_down_mask	power down mask
  * @pwr_down_mode	current power down mode
+ * @data:		transfer buffer
  */
-
 struct ad5504_state {
 	struct spi_device		*spi;
 	struct regulator		*reg;
 	unsigned short			vref_mv;
 	unsigned			pwr_down_mask;
 	unsigned			pwr_down_mode;
+
+	__be16				data[2] ____cacheline_aligned;
 };
 
 /**
@@ -66,31 +68,29 @@ enum ad5504_supported_device_ids {
 	ID_AD5501,
 };
 
-static int ad5504_spi_write(struct spi_device *spi, u8 addr, u16 val)
+static int ad5504_spi_write(struct ad5504_state *st, u8 addr, u16 val)
 {
-	__be16 tmp = cpu_to_be16(AD5504_CMD_WRITE |
-			      AD5504_ADDR(addr) |
+	st->data[0] = cpu_to_be16(AD5504_CMD_WRITE | AD5504_ADDR(addr) |
 			      (val & AD5504_RES_MASK));
 
-	return spi_write(spi, (u8 *)&tmp, 2);
+	return spi_write(st->spi, &st->data[0], 2);
 }
 
-static int ad5504_spi_read(struct spi_device *spi, u8 addr)
+static int ad5504_spi_read(struct ad5504_state *st, u8 addr)
 {
-	__be16 tmp = cpu_to_be16(AD5504_CMD_READ | AD5504_ADDR(addr));
-	__be16 val;
 	int ret;
-	struct spi_transfer	t = {
-			.tx_buf		= &tmp,
-			.rx_buf		= &val,
-			.len		= 2,
-		};
-	ret = spi_sync_transfer(spi, &t, 1);
-
+	struct spi_transfer t = {
+	    .tx_buf = &st->data[0],
+	    .rx_buf = &st->data[1],
+	    .len = 2,
+	};
+
+	st->data[0] = cpu_to_be16(AD5504_CMD_READ | AD5504_ADDR(addr));
+	ret = spi_sync_transfer(st->spi, &t, 1);
 	if (ret < 0)
 		return ret;
 
-	return be16_to_cpu(val) & AD5504_RES_MASK;
+	return be16_to_cpu(st->data[1]) & AD5504_RES_MASK;
 }
 
 static int ad5504_read_raw(struct iio_dev *indio_dev,
@@ -104,7 +104,7 @@ static int ad5504_read_raw(struct iio_dev *indio_dev,
 
 	switch (m) {
 	case IIO_CHAN_INFO_RAW:
-		ret = ad5504_spi_read(st->spi, chan->address);
+		ret = ad5504_spi_read(st, chan->address);
 		if (ret < 0)
 			return ret;
 
@@ -133,7 +133,7 @@ static int ad5504_write_raw(struct iio_dev *indio_dev,
 		if (val >= (1 << chan->scan_type.realbits) || val < 0)
 			return -EINVAL;
 
-		return ad5504_spi_write(st->spi, chan->address, val);
+		return ad5504_spi_write(st, chan->address, val);
 	default:
 		ret = -EINVAL;
 	}
@@ -197,12 +197,12 @@ static ssize_t ad5504_write_dac_powerdown(struct iio_dev *indio_dev,
 	else
 		st->pwr_down_mask &= ~(1 << chan->channel);
 
-	ret = ad5504_spi_write(st->spi, AD5504_ADDR_CTRL,
+	ret = ad5504_spi_write(st, AD5504_ADDR_CTRL,
 				AD5504_DAC_PWRDWN_MODE(st->pwr_down_mode) |
 				AD5504_DAC_PWR(st->pwr_down_mask));
 
 	/* writes to the CTRL register must be followed by a NOOP */
-	ad5504_spi_write(st->spi, AD5504_ADDR_NOOP, 0);
+	ad5504_spi_write(st, AD5504_ADDR_NOOP, 0);
 
 	return ret ? ret : len;
 }