iio: magnetometer: bmc150: add mount matrix support

This patch allows to read a mount-matrix device tree
property and report to user-space or in-kernel iio
clients.
Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/magnetometer/bmc150_magn.c

@@ -143,6 +143,7 @@ struct bmc150_magn_data {
 	 */
 	struct mutex mutex;
 	struct regmap *regmap;
+	struct iio_mount_matrix orientation;
 	/* 4 x 32 bits for x, y z, 4 bytes align, 64 bits timestamp */
 	s32 buffer[6];
 	struct iio_trigger *dready_trig;
@@ -612,6 +613,20 @@ static ssize_t bmc150_magn_show_samp_freq_avail(struct device *dev,
 	return len;
 }
 
+static const struct iio_mount_matrix *
+bmc150_magn_get_mount_matrix(const struct iio_dev *indio_dev,
+			      const struct iio_chan_spec *chan)
+{
+	struct bmc150_magn_data *data = iio_priv(indio_dev);
+
+	return &data->orientation;
+}
+
+static const struct iio_chan_spec_ext_info bmc150_magn_ext_info[] = {
+	IIO_MOUNT_MATRIX(IIO_SHARED_BY_DIR, bmc150_magn_get_mount_matrix),
+	{ }
+};
+
 static IIO_DEV_ATTR_SAMP_FREQ_AVAIL(bmc150_magn_show_samp_freq_avail);
 
 static struct attribute *bmc150_magn_attributes[] = {
@@ -638,6 +653,7 @@ static const struct attribute_group bmc150_magn_attrs_group = {
 		.storagebits = 32,					\
 		.endianness = IIO_LE					\
 	},								\
+	.ext_info = bmc150_magn_ext_info,				\
 }
 
 static const struct iio_chan_spec bmc150_magn_channels[] = {
@@ -861,6 +877,11 @@ int bmc150_magn_probe(struct device *dev, struct regmap *regmap,
 	data->irq = irq;
 	data->dev = dev;
 
+	ret = iio_read_mount_matrix(dev, "mount-matrix",
+				&data->orientation);
+	if (ret)
+		return ret;
+
 	if (!name && ACPI_HANDLE(dev))
 		name = bmc150_magn_match_acpi_device(dev);