Re: [PATCH v2 06/20] iio: dummy: Use a fixed structure to build up scan to push to buffers.

["Nuno Sá" <noname.nuno@gmail.com>]

On Sun, 2025-04-06 at 18:19 +0100, Jonathan Cameron wrote:
> From: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> 
> It has long been discouraged for drivers to make use of iio_dev->scan_bytes
> directly as that is an implementation detail of the core. As such our
> example driver should definitely not be doing so.
> 
> A simple anonymous structure definition suffices here as even though
> we have a mixture of signed and unsigned channels only the signed ones
> use the full storage so the unsigned channels can used signed types as
> well.
> 
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> ---
> v2: Add a comment about stack buffers not being DMA safe.
> ---

Reviewed-by: Nuno Sá <nuno.sa@analog.com>

>  drivers/iio/dummy/iio_simple_dummy_buffer.c | 20 ++++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/iio/dummy/iio_simple_dummy_buffer.c
> b/drivers/iio/dummy/iio_simple_dummy_buffer.c
> index 288880346707..eca5f0652d23 100644
> --- a/drivers/iio/dummy/iio_simple_dummy_buffer.c
> +++ b/drivers/iio/dummy/iio_simple_dummy_buffer.c
> @@ -46,11 +46,14 @@ static irqreturn_t iio_simple_dummy_trigger_h(int irq,
> void *p)
>  	struct iio_poll_func *pf = p;
>  	struct iio_dev *indio_dev = pf->indio_dev;
>  	int i = 0, j;
> -	u16 *data;
> -
> -	data = kzalloc(indio_dev->scan_bytes, GFP_KERNEL);
> -	if (!data)
> -		goto done;
> +	/*
> +	 * Note that some buses such as SPI require DMA safe buffers which
> +	 * cannot be on the stack.
> +	 */
> +	struct {
> +		s16 data[ARRAY_SIZE(fakedata)];
> +		aligned_s64 timestamp;
> +	} scan;
>  
>  	/*
>  	 * Three common options here:
> @@ -69,14 +72,11 @@ static irqreturn_t iio_simple_dummy_trigger_h(int irq,
> void *p)
>  	 * constant table fakedata.
>  	 */
>  	iio_for_each_active_channel(indio_dev, j)
> -		data[i++] = fakedata[j];
> +		scan.data[i++] = fakedata[j];
>  
> -	iio_push_to_buffers_with_timestamp(indio_dev, data,
> +	iio_push_to_buffers_with_timestamp(indio_dev, &scan,
>  					   iio_get_time_ns(indio_dev));
>  
> -	kfree(data);
> -
> -done:
>  	/*
>  	 * Tell the core we are done with this trigger and ready for the
>  	 * next one.