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authorGregor Boirie <gregor.boirie@parrot.com>2016-04-20 20:23:43 +0300
committerJonathan Cameron <jic23@kernel.org>2016-04-24 00:13:05 +0300
commitdfc57732ad38f93ae6232a3b4e64fd077383a0f1 (patch)
tree180c004346687cc3d6204239a25bc630c30ea569 /Documentation/ABI/testing/sysfs-bus-iio
parentdc2c57153ec5119eae7770042197eff627184d74 (diff)
downloadlinux-dfc57732ad38f93ae6232a3b4e64fd077383a0f1.tar.xz
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 <gregor.boirie@parrot.com> Signed-off-by: Jonathan Cameron <jic23@kernel.org>
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diff --git a/Documentation/ABI/testing/sysfs-bus-iio b/Documentation/ABI/testing/sysfs-bus-iio
index f155eff910f9..ba8df69d40b0 100644
--- a/Documentation/ABI/testing/sysfs-bus-iio
+++ b/Documentation/ABI/testing/sysfs-bus-iio
@@ -1512,3 +1512,54 @@ Contact: linux-iio@vger.kernel.org
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: linux-iio@vger.kernel.org
+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.