iio: imu: st_lsm6dsx: add mount matrix support

Allow to read the mount-matrix device tree property and provide the
mount_matrix file for userspace to read.

Signed-off-by: Martin Kepplinger <[e-mail]>
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h

···
 		.endianness = IIO_LE,					\
 	},								\
 	.event_spec = &st_lsm6dsx_event,				\
+	.ext_info = st_lsm6dsx_accel_ext_info,				\
 	.num_event_specs = 1,						\
 }
 
···
  * @enable_event: enabled event bitmask.
  * @iio_devs: Pointers to acc/gyro iio_dev instances.
  * @settings: Pointer to the specific sensor settings in use.
+ * @orientation: sensor chip orientation relative to main hardware.
  */
 struct st_lsm6dsx_hw {
 	struct device *dev;
···
 	struct iio_dev *iio_devs[ST_LSM6DSX_ID_MAX];
 
 	const struct st_lsm6dsx_settings *settings;
+
+	struct iio_mount_matrix orientation;
 };
 
 static __maybe_unused const struct iio_event_spec st_lsm6dsx_event = {
···
 
 	return err;
 }
+
+static const inline struct iio_mount_matrix *
+st_lsm6dsx_get_mount_matrix(const struct iio_dev *iio_dev,
+			    const struct iio_chan_spec *chan)
+{
+	struct st_lsm6dsx_sensor *sensor = iio_priv(iio_dev);
+	struct st_lsm6dsx_hw *hw = sensor->hw;
+
+	return &hw->orientation;
+}
+
+static const struct iio_chan_spec_ext_info st_lsm6dsx_accel_ext_info[] = {
+	IIO_MOUNT_MATRIX(IIO_SHARED_BY_ALL, st_lsm6dsx_get_mount_matrix),
+	{ }
+};
 
 #endif /* ST_LSM6DSX_H */

drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c

···
 			return err;
 	}
 
+	err = iio_read_mount_matrix(hw->dev, "mount-matrix", &hw->orientation);
+	if (err)
+		return err;
+
 	for (i = 0; i < ST_LSM6DSX_ID_MAX; i++) {
 		if (!hw->iio_devs[i])
 			continue;