[PATCH v3 0/6] iio: introduce IIO_DECLARE_BUFFER_WITH_TS

David Lechner
2025-04-25T21:14:22Z

Creating a buffer of the proper size and correct alignment for use with
iio_push_to_buffers_with_ts() is commonly used and not easy to get
right (as seen by a number of recent fixes on the mailing list).

In general, we prefer to use this pattern for creating such buffers:

struct {
u16 data[2];
aligned_s64 timestamp;
} buffer;

However, there are many cases where a driver may have a large number of
channels that can be optionally enabled or disabled in a scan or the
driver might support a range of chips that have different numbers of
channels or different storage sizes for the data. In these cases, the
timestamp may not always be at the same place relative to the data. To
handle these, we allocate a buffer large enough for the largest possible
case and don't care exactly where the timestamp ends up in the buffer.

For these cases, we propose to introduce new macros to make it easier
it easier for both the authors to get it right and for readers of the
code to not have to do all of the math to verify that it is correct.

I have just included a few examples of drivers that can make use of this
new macro, but there are dozens more.

---
Changes in v3:
- Fixed a few mistakes, style issues and incorporate other feedback (see
individual commit message changelogs for details).
- Link to v2: https://lore.kernel.org/r/20250422-iio-introduce-iio_declare_buffer_with_ts-v2-0-3fd36475c706@baylibre.com

Changes in v2:
- Add 2nd macro for case where we need DMA alignment.
- Add new patch for ad4695 to convert buffer from u8 to u16 before
making use of the new macro.
- Drop the bmp280 patch since it was determined to have a better
alternative not using these macros.
- Add a few more examples to show the non-DMA case, both in a struct and
stack allocated.
- Link to v1: https://lore.kernel.org/r/20250418-iio-introduce-iio_declare_buffer_with_ts-v1-0-ee0c62a33a0f@baylibre.com

---
David Lechner (6):
iio: introduce IIO_DECLARE_BUFFER_WITH_TS macros
iio: adc: ad4695: use u16 for buffer elements
iio: adc: ad4695: use IIO_DECLARE_DMA_BUFFER_WITH_TS
iio: adc: ad7380: use IIO_DECLARE_DMA_BUFFER_WITH_TS
iio: accel: sca3300: use IIO_DECLARE_BUFFER_WITH_TS
iio: adc: at91-sama5d2: use IIO_DECLARE_BUFFER_WITH_TS

drivers/iio/accel/sca3300.c | 18 ++----------------
drivers/iio/adc/ad4695.c | 8 ++------
drivers/iio/adc/ad7380.c | 3 +--
drivers/iio/adc/at91-sama5d2_adc.c | 13 ++-----------
include/linux/iio/iio.h | 38 ++++++++++++++++++++++++++++++++++++++
5 files changed, 45 insertions(+), 35 deletions(-)
---
base-commit: aff301f37e220970c2f301b5c65a8bfedf52058e
change-id: 20250418-iio-introduce-iio_declare_buffer_with_ts-2f8773f7dad6

Best regards,
--
David Lechner <dlechner@baylibre.com>