[PATCH v2] iio: commom: st_sensors: ensure proper DMA alignment

[PATCH v2] iio: commom: st_sensors: ensure proper DMA alignment

[Nuno Sa]

Aligning the buffer to the L1 cache is not sufficient in some platforms
as they might have larger cacheline sizes for caches after L1 and thus,
we can't guarantee DMA safety.

That was the whole reason to introduce IIO_DMA_MINALIGN in [1]. Do the same
for st_sensors common buffer.

While at it, moved the odr_lock before buffer_data as we definitely
don't want any other data to share a cacheline with the buffer.

[1]: https://lore.kernel.org/linux-iio/20220508175712.647246-2-jic23@kernel.org/

Fixes: e031d5f558f1 ("iio:st_sensors: remove buffer allocation at each buffer enable")
Signed-off-by: Nuno Sa <nuno.sa@analog.com>
---
Changes in v2:
 * moved struct odr_lock before buffer_data.
---
 include/linux/iio/common/st_sensors.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/iio/common/st_sensors.h b/include/linux/iio/common/st_sensors.h
index 607c3a89a647..f9ae5cdd884f 100644
--- a/include/linux/iio/common/st_sensors.h
+++ b/include/linux/iio/common/st_sensors.h
@@ -258,9 +258,9 @@ struct st_sensor_data {
 	bool hw_irq_trigger;
 	s64 hw_timestamp;
 
-	char buffer_data[ST_SENSORS_MAX_BUFFER_SIZE] ____cacheline_aligned;
-
 	struct mutex odr_lock;
+
+	char buffer_data[ST_SENSORS_MAX_BUFFER_SIZE] __aligned(IIO_DMA_MINALIGN);
 };
 
 #ifdef CONFIG_IIO_BUFFER

---
base-commit: 1380d453434e276355458e712c743dd071ca1fa7
change-id: 20240131-dev_dma_safety_stm-7c09782d87ed
--

Thanks!
- Nuno Sá

Re: [PATCH v2] iio: commom: st_sensors: ensure proper DMA alignment

[Jonathan Cameron]

On Wed, 31 Jan 2024 10:16:47 +0100
Nuno Sa <nuno.sa@analog.com> wrote:

> Aligning the buffer to the L1 cache is not sufficient in some platforms
> as they might have larger cacheline sizes for caches after L1 and thus,
> we can't guarantee DMA safety.
> 
> That was the whole reason to introduce IIO_DMA_MINALIGN in [1]. Do the same
> for st_sensors common buffer.
> 
> While at it, moved the odr_lock before buffer_data as we definitely
> don't want any other data to share a cacheline with the buffer.
> 
> [1]: https://lore.kernel.org/linux-iio/20220508175712.647246-2-jic23@kernel.org/
> 
> Fixes: e031d5f558f1 ("iio:st_sensors: remove buffer allocation at each buffer enable")
> Signed-off-by: Nuno Sa <nuno.sa@analog.com>
Applied to the fixes-togreg branch of iio.git and marked for stable. Thanks!

Jonathan

> ---
> Changes in v2:
>  * moved struct odr_lock before buffer_data.
> ---
>  include/linux/iio/common/st_sensors.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/iio/common/st_sensors.h b/include/linux/iio/common/st_sensors.h
> index 607c3a89a647..f9ae5cdd884f 100644
> --- a/include/linux/iio/common/st_sensors.h
> +++ b/include/linux/iio/common/st_sensors.h
> @@ -258,9 +258,9 @@ struct st_sensor_data {
>  	bool hw_irq_trigger;
>  	s64 hw_timestamp;
>  
> -	char buffer_data[ST_SENSORS_MAX_BUFFER_SIZE] ____cacheline_aligned;
> -
>  	struct mutex odr_lock;
> +
> +	char buffer_data[ST_SENSORS_MAX_BUFFER_SIZE] __aligned(IIO_DMA_MINALIGN);
>  };
>  
>  #ifdef CONFIG_IIO_BUFFER
> 
> ---
> base-commit: 1380d453434e276355458e712c743dd071ca1fa7
> change-id: 20240131-dev_dma_safety_stm-7c09782d87ed
> --
> 
> Thanks!
> - Nuno Sá
>