iio:core: mounting matrix support
Expose a rotation matrix to indicate userspace the chip placement with
respect to the overall hardware system. This is needed to adjust
coordinates sampled from a sensor chip when its position deviates from the
main hardware system.
Final coordinates computation is delegated to userspace since:
* computation may involve floating point arithmetics ;
* it allows an application to combine adjustments with arbitrary
transformations.
This 3 dimentional space rotation matrix is expressed as 3x3 array of
strings to support floating point numbers. It may be retrieved from a
"[<dir>_][<type>_]mount_matrix" sysfs attribute file. It is declared into a
device / driver specific DTS property or platform data.
Signed-off-by: Gregor Boirie <[email protected]>
Signed-off-by: Jonathan Cameron <[email protected]>
diff --git a/Documentation/ABI/testing/sysfs-bus-iio b/Documentation/ABI/testing/sysfs-bus-iio
index f155eff..ba8df69 100644
--- a/Documentation/ABI/testing/sysfs-bus-iio
+++ b/Documentation/ABI/testing/sysfs-bus-iio
@@ -1512,3 +1512,54 @@
Description:
Raw (unscaled no offset etc.) pH reading of a substance as a negative
base-10 logarithm of hydrodium ions in a litre of water.
+
+What: /sys/bus/iio/devices/iio:deviceX/mount_matrix
+What: /sys/bus/iio/devices/iio:deviceX/in_mount_matrix
+What: /sys/bus/iio/devices/iio:deviceX/out_mount_matrix
+KernelVersion: 4.6
+Contact: [email protected]
+Description:
+ Mounting matrix for IIO sensors. This is a rotation matrix which
+ informs userspace about sensor chip's placement relative to the
+ main hardware it is mounted on.
+ Main hardware placement is defined according to the local
+ reference frame related to the physical quantity the sensor
+ measures.
+ Given that the rotation matrix is defined in a board specific
+ way (platform data and / or device-tree), the main hardware
+ reference frame definition is left to the implementor's choice
+ (see below for a magnetometer example).
+ Applications should apply this rotation matrix to samples so
+ that when main hardware reference frame is aligned onto local
+ reference frame, then sensor chip reference frame is also
+ perfectly aligned with it.
+ Matrix is a 3x3 unitary matrix and typically looks like
+ [0, 1, 0; 1, 0, 0; 0, 0, -1]. Identity matrix
+ [1, 0, 0; 0, 1, 0; 0, 0, 1] means sensor chip and main hardware
+ are perfectly aligned with each other.
+
+ For example, a mounting matrix for a magnetometer sensor informs
+ userspace about sensor chip's ORIENTATION relative to the main
+ hardware.
+ More specifically, main hardware orientation is defined with
+ respect to the LOCAL EARTH GEOMAGNETIC REFERENCE FRAME where :
+ * Y is in the ground plane and positive towards magnetic North ;
+ * X is in the ground plane, perpendicular to the North axis and
+ positive towards the East ;
+ * Z is perpendicular to the ground plane and positive upwards.
+
+ An implementor might consider that for a hand-held device, a
+ 'natural' orientation would be 'front facing camera at the top'.
+ The main hardware reference frame could then be described as :
+ * Y is in the plane of the screen and is positive towards the
+ top of the screen ;
+ * X is in the plane of the screen, perpendicular to Y axis, and
+ positive towards the right hand side of the screen ;
+ * Z is perpendicular to the screen plane and positive out of the
+ screen.
+ Another example for a quadrotor UAV might be :
+ * Y is in the plane of the propellers and positive towards the
+ front-view camera;
+ * X is in the plane of the propellers, perpendicular to Y axis,
+ and positive towards the starboard side of the UAV ;
+ * Z is perpendicular to propellers plane and positive upwards.
