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@xxxxxxxxxx>
---
Documentation/ABI/testing/sysfs-bus-iio | 51 ++++++++++++++++++++
drivers/iio/industrialio-core.c | 82 +++++++++++++++++++++++++++++++++
include/linux/iio/iio.h | 31 +++++++++++++
3 files changed, 164 insertions(+)
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 @@ Contact: linux-iio@xxxxxxxxxxxxxxx
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@xxxxxxxxxxxxxxx
+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.
diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
index 190a593..e6319a9 100644
--- a/drivers/iio/industrialio-core.c
+++ b/drivers/iio/industrialio-core.c
@@ -412,6 +412,88 @@ ssize_t iio_enum_write(struct iio_dev *indio_dev,
}
EXPORT_SYMBOL_GPL(iio_enum_write);
+static const struct iio_mount_matrix iio_mount_idmatrix = {
+ .rotation = {
+ "1", "0", "0",
+ "0", "1", "0",
+ "0", "0", "1"
+ }
+};
+
+static int iio_setup_mount_idmatrix(const struct device *dev,
+ struct iio_mount_matrix *matrix)
+{
+ *matrix = iio_mount_idmatrix;
+ dev_info(dev, "mounting matrix not found: using identity...\n");
+ return 0;
+}
+
+ssize_t iio_show_mount_matrix(struct iio_dev *indio_dev, uintptr_t priv,
+ const struct iio_chan_spec *chan, char *buf)
+{
+ const struct iio_mount_matrix *mtx = ((iio_get_mount_matrix_t *)
+ priv)(indio_dev, chan);
+
+ if (IS_ERR(mtx))
+ return PTR_ERR(mtx);
+
+ if (!mtx)
+ mtx = &iio_mount_idmatrix;
+
+ return snprintf(buf, PAGE_SIZE, "%s, %s, %s; %s, %s, %s; %s, %s, %s\n",
+ mtx->rotation[0], mtx->rotation[1], mtx->rotation[2],
+ mtx->rotation[3], mtx->rotation[4], mtx->rotation[5],
+ mtx->rotation[6], mtx->rotation[7], mtx->rotation[8]);
+}
+EXPORT_SYMBOL_GPL(iio_show_mount_matrix);
+
+/**
+ * of_iio_read_mount_matrix() - retrieve iio device mounting matrix from
+ * device-tree "mount-matrix" property
+ * @dev: device the mounting matrix property is assigned to
+ * @propname: device specific mounting matrix property name
+ * @matrix: where to store retrieved matrix
+ *
+ * If device is assigned no mounting matrix property, a default 3x3 identity
+ * matrix will be filled in.
+ *
+ * Return: 0 if success, or a negative error code on failure.
+ */
+#ifdef CONFIG_OF
+int of_iio_read_mount_matrix(const struct device *dev,
+ const char *propname,
+ struct iio_mount_matrix *matrix)
+{
+ if (dev->of_node) {
+ int err = of_property_read_string_array(dev->of_node,
+ propname, matrix->rotation,
+ ARRAY_SIZE(iio_mount_idmatrix.rotation));
+
+ if (err == ARRAY_SIZE(iio_mount_idmatrix.rotation))
+ return 0;
+
+ if (err >= 0)
+ /* Invalid number of matrix entries. */
+ return -EINVAL;
+
+ if (err != -EINVAL)
+ /* Invalid matrix declaration format. */
+ return err;
+ }
+
+ /* Matrix was not declared at all: fallback to identity. */
+ return iio_setup_mount_idmatrix(dev, matrix);
+}
+#else
+int of_iio_read_mount_matrix(const struct device *dev,
+ const char *propname,
+ struct iio_mount_matrix *matrix)
+{
+ return iio_setup_mount_idmatrix(dev, matrix);
+}
+#endif
+EXPORT_SYMBOL(of_iio_read_mount_matrix);
+
/**
* iio_format_value() - Formats a IIO value into its string representation
* @buf: The buffer to which the formatted value gets written
diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
index 0b2773a..7c29cb0 100644
--- a/include/linux/iio/iio.h
+++ b/include/linux/iio/iio.h
@@ -148,6 +148,37 @@ ssize_t iio_enum_write(struct iio_dev *indio_dev,
}
/**
+ * struct iio_mount_matrix - iio mounting matrix
+ * @rotation: 3 dimensional space rotation matrix defining sensor alignment with
+ * main hardware
+ */
+struct iio_mount_matrix {
+ const char *rotation[9];
+};
+
+ssize_t iio_show_mount_matrix(struct iio_dev *indio_dev, uintptr_t priv,
+ const struct iio_chan_spec *chan, char *buf);
+int of_iio_read_mount_matrix(const struct device *dev, const char *propname,
+ struct iio_mount_matrix *matrix);
+
+typedef const struct iio_mount_matrix *
+ (iio_get_mount_matrix_t)(const struct iio_dev *indio_dev,
+ const struct iio_chan_spec *chan);
+
+/**
+ * IIO_MOUNT_MATRIX() - Initialize mount matrix extended channel attribute
+ * @_shared: Whether the attribute is shared between all channels
+ * @_get: Pointer to an iio_get_mount_matrix_t accessor
+ */
+#define IIO_MOUNT_MATRIX(_shared, _get) \
+{ \
+ .name = "mount_matrix", \
+ .shared = (_shared), \
+ .read = iio_show_mount_matrix, \
+ .private = (uintptr_t)(_get), \
+}
+
+/**
* struct iio_event_spec - specification for a channel event
* @type: Type of the event
* @dir: Direction of the event
--
2.1.4
--
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