staging:iio:ad7280a: Do not store transfer buffer on the stack

Some I2C 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/staging/iio/adc/ad7280a.c

@@ -134,6 +134,8 @@ struct ad7280_state {
 	unsigned char			aux_threshhigh;
 	unsigned char			aux_threshlow;
 	unsigned char			cb_mask[AD7280A_MAX_CHAIN];
+
+	__be32				buf[2] ____cacheline_aligned;
 };
 
 static void ad7280_crc8_build_table(unsigned char *crc_tab)
@@ -189,22 +191,22 @@ static void ad7280_delay(struct ad7280_state *st)
 		msleep(1);
 }
 
-static int __ad7280_read32(struct spi_device *spi, unsigned *val)
+static int __ad7280_read32(struct ad7280_state *st, unsigned *val)
 {
-	__be32 rx_buf, tx_buf = cpu_to_be32(AD7280A_READ_TXVAL);
 	int ret;
-
 	struct spi_transfer t = {
-		.tx_buf	= &tx_buf,
-		.rx_buf = &rx_buf,
+		.tx_buf	= &st->buf[0],
+		.rx_buf = &st->buf[1],
 		.len = 4,
 	};
 
-	ret = spi_sync_transfer(spi, &t, 1);
+	st->buf[0] = cpu_to_be32(AD7280A_READ_TXVAL);
+
+	ret = spi_sync_transfer(st->spi, &t, 1);
 	if (ret)
 		return ret;
 
-	*val = be32_to_cpu(rx_buf);
+	*val = be32_to_cpu(st->buf[1]);
 
 	return 0;
 }
@@ -214,12 +216,11 @@ static int ad7280_write(struct ad7280_state *st, unsigned devaddr,
 {
 	unsigned reg = (devaddr << 27 | addr << 21 |
 			(val & 0xFF) << 13 | all << 12);
-	__be32 tx_buf;
 
 	reg |= ad7280_calc_crc8(st->crc_tab, reg >> 11) << 3 | 0x2;
-	tx_buf = cpu_to_be32(reg);
+	st->buf[0] = cpu_to_be32(reg);
 
-	return spi_write(st->spi, &tx_buf, 4);
+	return spi_write(st->spi, &st->buf[0], 4);
 }
 
 static int ad7280_read(struct ad7280_state *st, unsigned devaddr,
@@ -249,7 +250,7 @@ static int ad7280_read(struct ad7280_state *st, unsigned devaddr,
 	if (ret)
 		return ret;
 
-	__ad7280_read32(st->spi, &tmp);
+	__ad7280_read32(st, &tmp);
 
 	if (ad7280_check_crc(st, tmp))
 		return -EIO;
@@ -287,7 +288,7 @@ static int ad7280_read_channel(struct ad7280_state *st, unsigned devaddr,
 
 	ad7280_delay(st);
 
-	__ad7280_read32(st->spi, &tmp);
+	__ad7280_read32(st, &tmp);
 
 	if (ad7280_check_crc(st, tmp))
 		return -EIO;
@@ -320,7 +321,7 @@ static int ad7280_read_all_channels(struct ad7280_state *st, unsigned cnt,
 	ad7280_delay(st);
 
 	for (i = 0; i < cnt; i++) {
-		__ad7280_read32(st->spi, &tmp);
+		__ad7280_read32(st, &tmp);
 
 		if (ad7280_check_crc(st, tmp))
 			return -EIO;
@@ -363,7 +364,7 @@ static int ad7280_chain_setup(struct ad7280_state *st)
 		return ret;
 
 	for (n = 0; n <= AD7280A_MAX_CHAIN; n++) {
-		__ad7280_read32(st->spi, &val);
+		__ad7280_read32(st, &val);
 		if (val == 0)
 			return n - 1;