[PATCH] 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
can corrupt stack memory when using DMA on some systems.

This change adds 4 bytes at the end of the current DMA buffer, which will
be used by the trigger handler.
This is required because the first 4 bytes are reserved for register data.

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>
---
 drivers/iio/adc/ad_sigma_delta.c       | 4 ++--
 include/linux/iio/adc/ad_sigma_delta.h | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/iio/adc/ad_sigma_delta.c b/drivers/iio/adc/ad_sigma_delta.c
index 86039e9ecaca..33297f26508a 100644
--- a/drivers/iio/adc/ad_sigma_delta.c
+++ b/drivers/iio/adc/ad_sigma_delta.c
@@ -395,11 +395,11 @@ 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->data[4];
 	unsigned int reg_size;
 	unsigned int data_reg;
-	uint8_t data[16];
 
-	memset(data, 0x00, 16);
+	memset(data, 0x00, 4);
 
 	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 a3a838dcf8e4..ac4ac4752c62 100644
--- a/include/linux/iio/adc/ad_sigma_delta.h
+++ b/include/linux/iio/adc/ad_sigma_delta.h
@@ -80,7 +80,7 @@ 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				data[8] ____cacheline_aligned;
 };
 
 static inline int ad_sigma_delta_set_channel(struct ad_sigma_delta *sd,
-- 
2.17.1