-----Ursprüngliche Nachricht-----
> Von: Lars Möllendorf <lars.moellendorf@xxxxxxxxxx>
> Gesendet: Freitag 13 Dezember 2019 14:58
> An: Jonathan Cameron <jic23@xxxxxxxxxx>; Hartmut Knaack <knaack.h@xxxxxx>; Lars-Peter Clausen <lars@xxxxxxxxxx>; Peter Meerwald-Stadler <pmeerw@xxxxxxxxxx>; linux-iio@xxxxxxxxxxxxxxx
> CC: Lars Möllendorf <lars.moellendorf@xxxxxxxxxx>
> Betreff: [PATCH v3] iio: buffer: align the size of scan bytes to size of the largest element
>
> Previous versions of `iio_compute_scan_bytes` only aligned each element
> to its own length (i.e. its own natural alignment). Because multiple
> consecutive sets of scan elements are buffered this does not work in
> case the computed scan bytes do not align with the natural alignment of
> the first scan element in the set.
>
> This commit fixes this by aligning the scan bytes to the natural
> alignment of the largest scan element in the set.
After re-reading my commit message, I come to the conclusion that it really is sufficient to align the scan bytes to the natural alignment of the *first* element. This would save us the `max()` comparisons for each bit. At the moment I am not at my workstation, but I could submit a v4 next Friday.
> Fixes: 959d2952d124 ("staging:iio: make iio_sw_buffer_preenable much more
> general.")
> Signed-off-by: Lars Möllendorf <lars.moellendorf@xxxxxxxxxx>
> ---
> v3:
> - Fix the problem description in the commit message
> - Add "Fixes" tag
>
> v2:
> - Fix subject of patch which marked it the first in a set of three.
> - Add a description of the problem in the commit message
>
> ---
> drivers/iio/industrialio-buffer.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
> index 5d05c38c4ba9..2f037cd59d53 100644
> --- a/drivers/iio/industrialio-buffer.c
> +++ b/drivers/iio/industrialio-buffer.c
> @@ -546,7 +546,7 @@ static int iio_compute_scan_bytes(struct iio_dev *indio_dev,
> const unsigned long *mask, bool timestamp)
> {
> unsigned bytes = 0;
> - int length, i;
> + int length, i, largest = 0;
>
> /* How much space will the demuxed element take? */
> for_each_set_bit(i, mask,
> @@ -554,13 +554,17 @@ static int iio_compute_scan_bytes(struct iio_dev *indio_dev,
> length = iio_storage_bytes_for_si(indio_dev, i);
> bytes = ALIGN(bytes, length);
> bytes += length;
> + largest = max(largest, length);
> }
>
> if (timestamp) {
> length = iio_storage_bytes_for_timestamp(indio_dev);
> bytes = ALIGN(bytes, length);
> bytes += length;
> + largest = max(largest, length);
> }
> +
> + bytes = ALIGN(bytes, largest);
> return bytes;
> }
>
> --
> 2.23.0
>
