Re: [PATCH v7 3/3] staging: iio: adc: ad7816: Fix DMA safety issues in SPI transfers

[Jonathan Cameron]

On Tue, 15 Sep 2026 10:59:39 +0300
Abdelnasser Hussein <abdelnasserhussein11@xxxxxxxxx> wrote:

> The SPI operations in this driver are not DMA safe:
> 1. spi_read() uses a stack-allocated buffer.
> 2. spi_write() in ad7816_spi_read() uses a struct member that shares a
>    cacheline with other variables.
> 3. spi_write() in ad7816_spi_write() passes a stack parameter by
>    reference.
> 
> Fix these violations by replacing all spi_read() and spi_write() calls
> with spi_write_then_read(). This safely handles DMA by internally
> allocating a bounce buffer for the transfers, avoiding cacheline
> sharing issues without needing dedicated aligned buffers.
> This implicitly corrects the size argument in read to sizeof(buf).
> 
> Fixes: 7024425db64a ("staging: iio: adc: new driver for AD7816 devices")
I tried to apply but having missed many of these in the path
have a git hook that checks fixes tags.

That commit doesn't exist.  Seems it is the fairly similar ID.

7924425db04a  which is downright odd as two digits are different.
Copy typing maybe?  Anyhow, fixed up and series applied.

Jonathan


> Signed-off-by: Abdelnasser Hussein <abdelnasserhussein11@xxxxxxxxx>
> ---
>  drivers/staging/iio/adc/ad7816.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/staging/iio/adc/ad7816.c b/drivers/staging/iio/adc/ad7816.c
> index c18093ca8a82..f76f0215119a 100644
> --- a/drivers/staging/iio/adc/ad7816.c
> +++ b/drivers/staging/iio/adc/ad7816.c
> @@ -74,7 +74,7 @@ static int ad7816_spi_read(struct ad7816_chip_info *chip, u16 *data)
>  
>  	gpiod_set_value(chip->rdwr_pin, 1);
>  	gpiod_set_value(chip->rdwr_pin, 0);
> -	ret = spi_write(spi_dev, &chip->channel_id, sizeof(chip->channel_id));
> +	ret = spi_write_then_read(spi_dev, &chip->channel_id, sizeof(chip->channel_id), NULL, 0);
>  	if (ret < 0) {
>  		dev_err(&spi_dev->dev, "SPI channel setting error\n");
>  		return ret;
> @@ -96,7 +96,7 @@ 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_write_then_read(spi_dev, NULL, 0, &buf, sizeof(buf));
>  	if (ret < 0) {
>  		dev_err(&spi_dev->dev, "SPI data read error\n");
>  		return ret;
> @@ -116,7 +116,7 @@ static int ad7816_spi_write(struct ad7816_chip_info *chip, u8 data)
>  
>  	gpiod_set_value(chip->rdwr_pin, 1);
>  	gpiod_set_value(chip->rdwr_pin, 0);
> -	ret = spi_write(spi_dev, &data, sizeof(data));
> +	ret = spi_write_then_read(spi_dev, &data, sizeof(data), NULL, 0);
>  	if (ret < 0)
>  		dev_err(&spi_dev->dev, "SPI oti data write error\n");
>