Re: [PATCH v2 1/2] iio: add IIO_DECLARE_QUATERNION() macro

[Francesco Lavra <flavra@baylibre.com>]

On Mon, 2026-03-16 at 14:56 -0500, David Lechner wrote:
...
> > As for the alignment, according to your patch at [1], when the repeat
> > number is not a power of two, it is (will be) rounded up to the next
> > power
> > of two (and this is consistent with what the lsm6dsx driver expects),
> > so
> > the alignment will be 8 bytes.
> 
> I think you are referring to the 8-byte alignment for the timestamp?
> 
> Patch [1] should make a difference when the timestamp is not enabled
> in a buffered read though.
> 
> When the timestamp is enabled, the buffer is going to be 16 bytes per
> sample no matter what because of the 8-byte alignment of the timestamp.
> 
> But if the timestamp is not enabled, then for 16-bit storagebits and
> repeat of 3, before the patch, the buffer would only be 6 bytes per
> sample, but after the patch would be 8 bytes per sample. This doesn't
> make a difference in the driver itself, but does make a difference to
> userspace that is reading the buffer.

I was referring to alignment in general, regardless of the timestamp being
enabled. From my understanding, the computed storage size is also used for
alignment. Anyway, yes, after [1] the storage size for the quaternion scan
element will be 8 bytes, with the last 2 bytes of each sample zeroed out.

> 
> > [1]
> > https://lore.kernel.org/linux-iio/20260307-iio-fix-timestamp-alignment-v2-4-d1d48fbadbbf@baylibre.com/