[PATCH v9 5/6] iio: ABI: Add quaternion axis modifier

[Francesco Lavra <flavra@baylibre.com>]

This modifier applies to the IIO_ROT channel type, and indicates a data
representation that specifies the {x, y, z} components of the normalized
quaternion vector.

Signed-off-by: Francesco Lavra <flavra@baylibre.com>
Reviewed-by: David Lechner <dlechner@baylibre.com>
---
The use of this modifier depends on [1] to get the correct sizing of the
buffer in userspace.

[1]: https://lore.kernel.org/linux-iio/20260307-iio-fix-timestamp-alignment-v2-4-d1d48fbadbbf@baylibre.com/
---
 Documentation/ABI/testing/sysfs-bus-iio | 15 +++++++++++++++
 drivers/iio/industrialio-core.c         |  1 +
 include/uapi/linux/iio/types.h          |  1 +
 tools/iio/iio_event_monitor.c           |  1 +
 4 files changed, 18 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-bus-iio b/Documentation/ABI/testing/sysfs-bus-iio
index bd6c3305dd2b..46fef26e5376 100644
--- a/Documentation/ABI/testing/sysfs-bus-iio
+++ b/Documentation/ABI/testing/sysfs-bus-iio
@@ -1755,6 +1755,21 @@ Description:
 		measurement from channel Y. Units after application of scale and
 		offset are milliamps.
 
+What:		/sys/bus/iio/devices/iio:deviceX/in_rot_quaternionaxis_raw
+KernelVersion:	7.1
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Raw value of {x, y, z} components of the quaternion vector. These
+		components represent the axis about which a rotation occurs, and are
+		subject to the following constraints:
+
+		- the quaternion vector is normalized, i.e. w^2 + x^2 + y^2 + z^2 = 1
+		- the rotation angle is within the [-pi, pi] range, i.e. the w
+		  component (which represents the amount of rotation) is non-negative
+
+		These constraints allow the w value to be calculated from the other
+		components: w = sqrt(1 - (x^2 + y^2 + z^2)).
+
 What:		/sys/.../iio:deviceX/in_energy_en
 What:		/sys/.../iio:deviceX/in_distance_en
 What:		/sys/.../iio:deviceX/in_velocity_sqrt(x^2+y^2+z^2)_en
diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
index 22eefd048ba9..bd6f4f9f4533 100644
--- a/drivers/iio/industrialio-core.c
+++ b/drivers/iio/industrialio-core.c
@@ -157,6 +157,7 @@ static const char * const iio_modifier_names[] = {
 	[IIO_MOD_ACTIVE] = "active",
 	[IIO_MOD_REACTIVE] = "reactive",
 	[IIO_MOD_APPARENT] = "apparent",
+	[IIO_MOD_QUATERNION_AXIS] = "quaternionaxis",
 };
 
 /* relies on pairs of these shared then separate */
diff --git a/include/uapi/linux/iio/types.h b/include/uapi/linux/iio/types.h
index 6d269b844271..d7c2bb223651 100644
--- a/include/uapi/linux/iio/types.h
+++ b/include/uapi/linux/iio/types.h
@@ -113,6 +113,7 @@ enum iio_modifier {
 	IIO_MOD_ACTIVE,
 	IIO_MOD_REACTIVE,
 	IIO_MOD_APPARENT,
+	IIO_MOD_QUATERNION_AXIS,
 };
 
 enum iio_event_type {
diff --git a/tools/iio/iio_event_monitor.c b/tools/iio/iio_event_monitor.c
index 03ca33869ce8..df6c43d7738d 100644
--- a/tools/iio/iio_event_monitor.c
+++ b/tools/iio/iio_event_monitor.c
@@ -145,6 +145,7 @@ static const char * const iio_modifier_names[] = {
 	[IIO_MOD_ACTIVE] = "active",
 	[IIO_MOD_REACTIVE] = "reactive",
 	[IIO_MOD_APPARENT] = "apparent",
+	[IIO_MOD_QUATERNION_AXIS] = "quaternionaxis",
 };
 
 static bool event_is_known(struct iio_event_data *event)
-- 
2.39.5