[PATCH v2] staging: iio: frequency: ad9832: Fix alignment for DMA safety

[PATCH v2] staging: iio: frequency: ad9832: Fix alignment for DMA safety

[Jonathan Cameron]

From: Jonathan Cameron <Jonathan.Cameron@huawei.com>

____cacheline_aligned is an insufficient guarantee for non-coherent DMA
on platforms with 128 byte cachelines above L1.  Switch to the updated
IIO_DMA_MINALIGN definition.  Whilst here, move the marking to cover
the whole union. That has not functional affect, but makes it slightly
easier to see what is going on.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

---
v2: Move the alignment marking to the union rather than an element in the
    union. (Andy Shevchenko)
 drivers/staging/iio/frequency/ad9832.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/iio/frequency/ad9832.c b/drivers/staging/iio/frequency/ad9832.c
index f43464db618a..6f9eebd6c7ee 100644
--- a/drivers/staging/iio/frequency/ad9832.c
+++ b/drivers/staging/iio/frequency/ad9832.c
@@ -112,10 +112,10 @@ struct ad9832_state {
 	 * transfer buffers to live in their own cache lines.
 	 */
 	union {
-		__be16			freq_data[4]____cacheline_aligned;
+		__be16			freq_data[4];
 		__be16			phase_data[2];
 		__be16			data;
-	};
+	} __aligned(IIO_DMA_MINALIGN);
 };
 
 static unsigned long ad9832_calc_freqreg(unsigned long mclk, unsigned long fout)
-- 
2.37.1

Re: [PATCH v2] staging: iio: frequency: ad9832: Fix alignment for DMA safety

[Andy Shevchenko]

On Sat, Aug 13, 2022 at 6:55 PM Jonathan Cameron <jic23@kernel.org> wrote:
>
> From: Jonathan Cameron <Jonathan.Cameron@huawei.com>
>
> ____cacheline_aligned is an insufficient guarantee for non-coherent DMA
> on platforms with 128 byte cachelines above L1.  Switch to the updated
> IIO_DMA_MINALIGN definition.  Whilst here, move the marking to cover
> the whole union. That has not functional affect, but makes it slightly

not --> no ?

> easier to see what is going on.

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>

> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
>
> ---
> v2: Move the alignment marking to the union rather than an element in the
>     union. (Andy Shevchenko)
>  drivers/staging/iio/frequency/ad9832.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/staging/iio/frequency/ad9832.c b/drivers/staging/iio/frequency/ad9832.c
> index f43464db618a..6f9eebd6c7ee 100644
> --- a/drivers/staging/iio/frequency/ad9832.c
> +++ b/drivers/staging/iio/frequency/ad9832.c
> @@ -112,10 +112,10 @@ struct ad9832_state {
>          * transfer buffers to live in their own cache lines.
>          */
>         union {
> -               __be16                  freq_data[4]____cacheline_aligned;
> +               __be16                  freq_data[4];
>                 __be16                  phase_data[2];
>                 __be16                  data;
> -       };
> +       } __aligned(IIO_DMA_MINALIGN);
>  };
>
>  static unsigned long ad9832_calc_freqreg(unsigned long mclk, unsigned long fout)
> --
> 2.37.1
>


-- 
With Best Regards,
Andy Shevchenko