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>

1 files changed, 31 insertions, 0 deletions

diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
index 0b2773ada0ba..7c29cb0124ae 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