[PATCH] staging: iio: ad7816: avoid DMA from stack in spi_read

[Abdelnasser Hussein]

The SPI core may use DMA for transfers. Using a stack-allocated
buffer for DMA is unsafe and can trigger faults when VMAP_STACK is
enabled, since the stack is not guaranteed to be DMA-accessible.

Move the transfer buffer from the stack into the ad7816_chip_info
structure so it has a stable lifetime suitable for DMA transfers.
Mark the buffer with ____cacheline_aligned to ensure proper alignment
for DMA operations.

Signed-off-by: Abdelnasser Hussein <abdelnasserhussein11@xxxxxxxxx>
---
 drivers/staging/iio/adc/ad7816.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/staging/iio/adc/ad7816.c b/drivers/staging/iio/adc/ad7816.c
index 0e32a2295990..fcaadebff0f4 100644
--- a/drivers/staging/iio/adc/ad7816.c
+++ b/drivers/staging/iio/adc/ad7816.c
@@ -50,6 +50,7 @@ struct ad7816_chip_info {
 	u8  oti_data[AD7816_CS_MAX + 1];
 	u8  channel_id;	/* 0 always be temperature */
 	u8  mode;
+	__be16 rx_buf ____cacheline_aligned;
 };
 
 enum ad7816_type {
@@ -65,7 +66,6 @@ static int ad7816_spi_read(struct ad7816_chip_info *chip, u16 *data)
 {
 	struct spi_device *spi_dev = chip->spi_dev;
 	int ret;
-	__be16 buf;
 
 	gpiod_set_value(chip->rdwr_pin, 1);
 	gpiod_set_value(chip->rdwr_pin, 0);
@@ -91,14 +91,12 @@ static int ad7816_spi_read(struct ad7816_chip_info *chip, u16 *data)
 
 	gpiod_set_value(chip->rdwr_pin, 0);
 	gpiod_set_value(chip->rdwr_pin, 1);
-	ret = spi_read(spi_dev, &buf, sizeof(*data));
+	ret = spi_read(spi_dev, &chip->rx_buf, sizeof(chip->rx_buf));
 	if (ret < 0) {
 		dev_err(&spi_dev->dev, "SPI data read error\n");
 		return ret;
 	}
-
-	*data = be16_to_cpu(buf);
-
+	*data = be16_to_cpu(chip->rx_buf);
 	return ret;
 }
 
-- 
2.54.0