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

[David Lechner <dlechner@baylibre.com>]

Add a new IIO_DECLARE_QUATERNION() macro that is used to declare the
field in an IIO buffer struct that contains a quaternion vector.

Quaternions are currently the only IIO data type that uses the .repeat
feature of struct iio_scan_type. This has an implicit rule that the
element in the buffer must be aligned to the entire size of the repeated
element. This macro will make that requirement explicit. Since this is
the only user, we just call the macro IIO_DECLARE_QUATERNION() instead
of something more generic.

Signed-off-by: David Lechner <dlechner@baylibre.com>
---
 include/linux/iio/iio.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
index a9ecff191bd9..2c91b7659ce9 100644
--- a/include/linux/iio/iio.h
+++ b/include/linux/iio/iio.h
@@ -931,6 +931,18 @@ static inline void *iio_device_get_drvdata(const struct iio_dev *indio_dev)
 #define IIO_DECLARE_DMA_BUFFER_WITH_TS(type, name, count) \
 	__IIO_DECLARE_BUFFER_WITH_TS(type, name, count) __aligned(IIO_DMA_MINALIGN)
 
+/**
+ * IIO_DECLARE_QUATERNION() - Declare a quaternion element
+ * @type: element type of the individual vectors
+ * @name: identifier name
+ *
+ * Quaternions are a vector composed of 4 elements (W, X, Y, Z). Use this macro
+ * to declare a quaternion element in a struct to ensure proper alignment in
+ * an IIO buffer.
+ */
+#define IIO_DECLARE_QUATERNION(type, name) \
+	type name[4] __aligned(sizeof(type) * 4)
+
 struct iio_dev *iio_device_alloc(struct device *parent, int sizeof_priv);
 
 /* The information at the returned address is guaranteed to be cacheline aligned */

-- 
2.43.0