[PATCH v2 0/5] iio: buffer: fix timestamp alignment (in rare case)

[David Lechner <dlechner@baylibre.com>]

In [1], it was pointed out that the iio_push_to_buffers_with_timestamp()
function is not putting the timestamp at the correct offset in the scan
buffer in rare cases where the largest scan element size is larger than
sizeof(int64_t).

[1]: https://lore.kernel.org/linux-iio/20260215162351.79f40b32@jic23-huawei/

This only affected one driver, namely hid-sensor-rotation since it is
the only driver that meets the condition. To fix things up, first we
fix the hid-sensor-rotation driver in a way that preserves compatibility
with the broken timestamp alignment. Then we are free to fix the core
IIO code without affecting any users.

The first patch depends on [2] which is now in iio/fixes-togreg. It
should be OK to apply the first patch there and let the rest of the
patches go through iio/togreg (the later patches are just preventing
future bugs).

[2]: https://lore.kernel.org/linux-iio/20260228-iio-fix-repeat-alignment-v2-0-d58bfaa2920d@baylibre.com/

Signed-off-by: David Lechner <dlechner@baylibre.com>
---
Changes in v2:
- Don't say "HACK" in comments.
- Cache timestamp offset instead of largest scan element size.
- New patch to ensure size/alignment is always power of 2 bytes.
- Link to v1: https://lore.kernel.org/r/20260301-iio-fix-timestamp-alignment-v1-0-1a54980bfb90@baylibre.com

---
David Lechner (5):
      iio: orientation: hid-sensor-rotation: add timestamp hack to not break userspace
      iio: buffer: check return value of iio_compute_scan_bytes()
      iio: buffer: cache timestamp offset in scan buffer
      iio: buffer: ensure repeat alignment is a power of two
      iio: buffer: fix timestamp alignment when quaternion in scan

 drivers/iio/industrialio-buffer.c             | 46 ++++++++++++++++++++-------
 drivers/iio/orientation/hid-sensor-rotation.c | 22 +++++++++++--
 include/linux/iio/buffer.h                    | 12 +++++--
 include/linux/iio/iio.h                       |  3 ++
 4 files changed, 66 insertions(+), 17 deletions(-)
---
base-commit: 6f25a6105c41a7d6b12986dbe80ded396a5667f8
change-id: 20260228-iio-fix-timestamp-alignment-89ade1af458b
prerequisite-message-id: <20260228-iio-fix-repeat-alignment-v2-0-d58bfaa2920d@baylibre.com>
prerequisite-patch-id: e155a526d57c5759a2fcfbfca7f544cb419addfd
prerequisite-patch-id: 6c69eaad0dd2ae69bd2745e7d387f739fc1a9ba0

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