[PATCH v2 4/5] iio: buffer: ensure repeat alignment is a power of two

[David Lechner]

Use roundup_pow_of_two() in the calculation of iio_storage_bytes_for_si()
when scan_type->repeat > 1 to ensure that the size is a power of two.
storagebits is always going to be a power of two bytes, so we only need
to apply this to the repeat factor. The storage size is also used for
alignment, and we want to ensure that all alignments are a power of two.

The only repeat in use in the kernel currently is for quaternions, which
have a repeat of 4, so this does not change the result for existing
users.

Signed-off-by: David Lechner <dlechner@xxxxxxxxxxxx>
---

v2 changes: new patch

In v1, Nuno made the point that if the size isn't a power of two, then
the alignment won't be a power of two either. And this could cause
unexpected problems regarding alignment in general.

This will affect the work Francesco is doing with IIO_MOD_QUATERNION_AXIS
which will have a repeat of 3, so this is a good time to think about this.
---
 drivers/iio/industrialio-buffer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
index ecfe0c9740e2..c38da24561c0 100644
--- a/drivers/iio/industrialio-buffer.c
+++ b/drivers/iio/industrialio-buffer.c
@@ -748,7 +748,7 @@ static int iio_storage_bytes_for_si(struct iio_dev *indio_dev,
 	bytes = scan_type->storagebits / 8;
 
 	if (scan_type->repeat > 1)
-		bytes *= scan_type->repeat;
+		bytes *= roundup_pow_of_two(scan_type->repeat);
 
 	return bytes;
 }

-- 
2.43.0