iio: accel: kxcjk1013: Support orientation matrix

Hardware could be physically mounted in any possible direction and
userpspace needs to be aware of the mounting orientation in order to
process sensor's data correctly. In particular this helps iio-sensor-proxy
to report display's orientation properly on a phone/tablet devices.

Signed-off-by: Dmitry Osipenko <[e-mail]>
Acked-by: Srinivas Pandruvada <[e-mail]>
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/iio/accel/kxcjk-1013.c

···
 	struct i2c_client *client;
 	struct iio_trigger *dready_trig;
 	struct iio_trigger *motion_trig;
+	struct iio_mount_matrix orientation;
 	struct mutex mutex;
 	s16 buffer[8];
 	u8 odr_bits;
···
 				 BIT(IIO_EV_INFO_PERIOD)
 };
 
+static const struct iio_mount_matrix *
+kxcjk1013_get_mount_matrix(const struct iio_dev *indio_dev,
+			   const struct iio_chan_spec *chan)
+{
+	struct kxcjk1013_data *data = iio_priv(indio_dev);
+
+	return &data->orientation;
+}
+
+static const struct iio_chan_spec_ext_info kxcjk1013_ext_info[] = {
+	IIO_MOUNT_MATRIX(IIO_SHARED_BY_TYPE, kxcjk1013_get_mount_matrix),
+	{ }
+};
+
 #define KXCJK1013_CHANNEL(_axis) {					\
 	.type = IIO_ACCEL,						\
 	.modified = 1,							\
···
 		.endianness = IIO_LE,					\
 	},								\
 	.event_spec = &kxcjk1013_event,				\
+	.ext_info = kxcjk1013_ext_info,					\
 	.num_event_specs = 1						\
 }
 
···
 	data->client = client;
 
 	pdata = dev_get_platdata(&client->dev);
-	if (pdata)
+	if (pdata) {
 		data->active_high_intr = pdata->active_high_intr;
-	else
+		data->orientation = pdata->orientation;
+	} else {
 		data->active_high_intr = true; /* default polarity */
+
+		ret = iio_read_mount_matrix(&client->dev, "mount-matrix",
+					    &data->orientation);
+		if (ret)
+			return ret;
+	}
 
 	if (id) {
 		data->chipset = (enum kx_chipset)(id->driver_data);

include/linux/iio/accel/kxcjk_1013.h

···
 #ifndef __IIO_KXCJK_1013_H__
 #define __IIO_KXCJK_1013_H__
 
+#include <linux/iio/iio.h>
+
 struct kxcjk_1013_platform_data {
 	bool active_high_intr;
+	struct iio_mount_matrix orientation;
 };
 
 #endif