[PATCH V2] iio: ad_sigma_delta: Don't put SPI transfer buffer on the stack

[Alexandru Ardelean <alexandru.ardelean@analog.com>]

From: Lars-Peter Clausen <lars@metafoo.de>

Use a heap allocated memory for the SPI transfer buffer. Using stack memory
will not work on some architectures when using DMA.

This also avoids potential stack corruption, as it makes sure that the
buffer is in it's own cacheline and (obviously) not on the stack.

Fixes: af3008485ea03 ("iio:adc: Add common code for ADI Sigma Delta devices")
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
---
Changelog v1 -> v2:
* added ____cacheline_aligned to `buf_data`
* extended comment about cacheline
* added fixes tag

 drivers/iio/adc/ad_sigma_delta.c       | 22 +++++++++++-----------
 include/linux/iio/adc/ad_sigma_delta.h |  3 ++-
 2 files changed, 13 insertions(+), 12 deletions(-)

diff --git a/drivers/iio/adc/ad_sigma_delta.c b/drivers/iio/adc/ad_sigma_delta.c
index af6cbc683214..02d9049b9218 100644
--- a/drivers/iio/adc/ad_sigma_delta.c
+++ b/drivers/iio/adc/ad_sigma_delta.c
@@ -58,7 +58,7 @@ EXPORT_SYMBOL_GPL(ad_sd_set_comm);
 int ad_sd_write_reg(struct ad_sigma_delta *sigma_delta, unsigned int reg,
 	unsigned int size, unsigned int val)
 {
-	uint8_t *data = sigma_delta->data;
+	uint8_t *data = sigma_delta->reg_data;
 	struct spi_transfer t = {
 		.tx_buf		= data,
 		.len		= size + 1,
@@ -102,7 +102,7 @@ EXPORT_SYMBOL_GPL(ad_sd_write_reg);
 static int ad_sd_read_reg_raw(struct ad_sigma_delta *sigma_delta,
 	unsigned int reg, unsigned int size, uint8_t *val)
 {
-	uint8_t *data = sigma_delta->data;
+	uint8_t *data = sigma_delta->reg_data;
 	int ret;
 	struct spi_transfer t[] = {
 		{
@@ -148,24 +148,24 @@ int ad_sd_read_reg(struct ad_sigma_delta *sigma_delta,
 {
 	int ret;
 
-	ret = ad_sd_read_reg_raw(sigma_delta, reg, size, sigma_delta->data);
+	ret = ad_sd_read_reg_raw(sigma_delta, reg, size, sigma_delta->reg_data);
 	if (ret < 0)
 		goto out;
 
 	switch (size) {
 	case 4:
-		*val = get_unaligned_be32(sigma_delta->data);
+		*val = get_unaligned_be32(sigma_delta->reg_data);
 		break;
 	case 3:
-		*val = (sigma_delta->data[0] << 16) |
-			(sigma_delta->data[1] << 8) |
-			sigma_delta->data[2];
+		*val = (sigma_delta->reg_data[0] << 16) |
+			(sigma_delta->reg_data[1] << 8) |
+			sigma_delta->reg_data[2];
 		break;
 	case 2:
-		*val = get_unaligned_be16(sigma_delta->data);
+		*val = get_unaligned_be16(sigma_delta->reg_data);
 		break;
 	case 1:
-		*val = sigma_delta->data[0];
+		*val = sigma_delta->reg_data[0];
 		break;
 	default:
 		ret = -EINVAL;
@@ -403,12 +403,12 @@ static irqreturn_t ad_sd_trigger_handler(int irq, void *p)
 	struct iio_poll_func *pf = p;
 	struct iio_dev *indio_dev = pf->indio_dev;
 	struct ad_sigma_delta *sigma_delta = iio_device_get_drvdata(indio_dev);
+	uint8_t *data = sigma_delta->buf_data;
 	unsigned int reg_size;
 	unsigned int data_reg;
-	uint8_t data[16];
 	int ret;
 
-	memset(data, 0x00, 16);
+	memset(sigma_delta->buf_data, 0x00, sizeof(sigma_delta->buf_data));
 
 	reg_size = indio_dev->channels[0].scan_type.realbits +
 			indio_dev->channels[0].scan_type.shift;
diff --git a/include/linux/iio/adc/ad_sigma_delta.h b/include/linux/iio/adc/ad_sigma_delta.h
index 6e9fb1932dde..d95216ce8a94 100644
--- a/include/linux/iio/adc/ad_sigma_delta.h
+++ b/include/linux/iio/adc/ad_sigma_delta.h
@@ -79,7 +79,8 @@ struct ad_sigma_delta {
 	 * DMA (thus cache coherency maintenance) requires the
 	 * transfer buffers to live in their own cache lines.
 	 */
-	uint8_t				data[4] ____cacheline_aligned;
+	uint8_t				reg_data[4] ____cacheline_aligned;
+	uint8_t				buf_data[16] ____cacheline_aligned;
 };
 
 static inline int ad_sigma_delta_set_channel(struct ad_sigma_delta *sd,
-- 
2.17.1