Message-Id: <20260109181528.154127-4-flavra@baylibre.com>
Date: Fri,  9 Jan 2026 19:15:28 +0100
From: Francesco Lavra <flavra@...libre.com>
To: Lorenzo Bianconi <lorenzo@...nel.org>,
	Jonathan Cameron <jic23@...nel.org>,
	David Lechner <dlechner@...libre.com>,
	Nuno Sá <nuno.sa@...log.com>,
	Andy Shevchenko <andy@...nel.org>,
	linux-iio@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 3/3] iio: imu: st_lsm6dsx: add support for rotation sensor

Some IMU chips in the LSM6DSX family have sensor fusion features that
combine data from the accelerometer and gyroscope. One of these features
generates rotation vector data and makes it available in the hardware
FIFO as a quaternion (more specifically, the X, Y and Z components of the
quaternion vector, expressed as 16-bit half-precision floating-point
numbers).

Add support for a new sensor instance that allows receiving sensor fusion
data, by defining a new struct st_lsm6dsx_sf_settings (which contains
chip-specific details for the sensor fusion functionality), and adding this
struct as a new field in struct st_lsm6dsx_settings. In st_lsm6dsx_core.c,
populate this new struct for the LSM6DSV and LSM6DSV16X chips, and add the
logic to initialize an additional IIO device if this struct is populated
for the hardware type being probed.
Note: a new IIO device is being defined (as opposed to adding channels to
an existing device) because each of the existing devices handles data
coming from a single sensor, while sensor fusion data comes from multiple
sensors.

Tested on LSMDSV16X.

Signed-off-by: Francesco Lavra <flavra@...libre.com>
---
 drivers/iio/imu/st_lsm6dsx/Makefile           |   2 +-
 drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h       |  26 +-
 .../iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c    |  16 +-
 drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c  |  58 +++++
 .../iio/imu/st_lsm6dsx/st_lsm6dsx_fusion.c    | 224 ++++++++++++++++++
 5 files changed, 319 insertions(+), 7 deletions(-)
 create mode 100644 drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_fusion.c

diff --git a/drivers/iio/imu/st_lsm6dsx/Makefile b/drivers/iio/imu/st_lsm6dsx/Makefile
index 57cbcd67d64f..19a488254de3 100644
--- a/drivers/iio/imu/st_lsm6dsx/Makefile
+++ b/drivers/iio/imu/st_lsm6dsx/Makefile
@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0-only
 st_lsm6dsx-y := st_lsm6dsx_core.o st_lsm6dsx_buffer.o \
-		st_lsm6dsx_shub.o
+		st_lsm6dsx_shub.o st_lsm6dsx_fusion.o
 
 obj-$(CONFIG_IIO_ST_LSM6DSX) += st_lsm6dsx.o
 obj-$(CONFIG_IIO_ST_LSM6DSX_I2C) += st_lsm6dsx_i2c.o
diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h
index 07b1773c87bd..4173f670f7af 100644
--- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h
+++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h
@@ -294,6 +294,7 @@ enum st_lsm6dsx_sensor_id {
 	ST_LSM6DSX_ID_EXT0,
 	ST_LSM6DSX_ID_EXT1,
 	ST_LSM6DSX_ID_EXT2,
+	ST_LSM6DSX_ID_SF,
 	ST_LSM6DSX_ID_MAX,
 };
 
@@ -301,6 +302,15 @@ enum st_lsm6dsx_ext_sensor_id {
 	ST_LSM6DSX_ID_MAGN,
 };
 
+struct st_lsm6dsx_sf_settings {
+	const struct iio_chan_spec *chan;
+	int chan_len;
+	struct st_lsm6dsx_odr_table_entry odr_table;
+	struct st_lsm6dsx_reg fifo_enable;
+	struct st_lsm6dsx_reg page_mux;
+	struct st_lsm6dsx_reg enable;
+};
+
 /**
  * struct st_lsm6dsx_ext_dev_settings - i2c controller slave settings
  * @i2c_addr: I2c slave address list.
@@ -388,6 +398,7 @@ struct st_lsm6dsx_settings {
 	struct st_lsm6dsx_hw_ts_settings ts_settings;
 	struct st_lsm6dsx_shub_settings shub_settings;
 	struct st_lsm6dsx_event_settings event_settings;
+	struct st_lsm6dsx_sf_settings sf_settings;
 };
 
 enum st_lsm6dsx_sensor_id {
@@ -510,6 +521,9 @@ int st_lsm6dsx_check_odr(struct st_lsm6dsx_sensor *sensor, u32 odr, u8 *val);
 int st_lsm6dsx_shub_probe(struct st_lsm6dsx_hw *hw, const char *name);
 int st_lsm6dsx_shub_set_enable(struct st_lsm6dsx_sensor *sensor, bool enable);
 int st_lsm6dsx_shub_read_output(struct st_lsm6dsx_hw *hw, u8 *data, int len);
+int st_lsm6dsx_sf_probe(struct st_lsm6dsx_hw *hw, const char *name);
+int st_lsm6dsx_sf_set_enable(struct st_lsm6dsx_sensor *sensor, bool enable);
+int st_lsm6dsx_sf_set_odr(struct st_lsm6dsx_sensor *sensor, bool enable);
 int st_lsm6dsx_set_page(struct st_lsm6dsx_hw *hw, bool enable);
 
 static inline int
@@ -564,12 +578,14 @@ st_lsm6dsx_get_mount_matrix(const struct iio_dev *iio_dev,
 static inline int
 st_lsm6dsx_device_set_enable(struct st_lsm6dsx_sensor *sensor, bool enable)
 {
-	if (sensor->id == ST_LSM6DSX_ID_EXT0 ||
-	    sensor->id == ST_LSM6DSX_ID_EXT1 ||
-	    sensor->id == ST_LSM6DSX_ID_EXT2)
+	switch (sensor->id) {
+	case ST_LSM6DSX_ID_EXT0 ... ST_LSM6DSX_ID_EXT2:
 		return st_lsm6dsx_shub_set_enable(sensor, enable);
-
-	return st_lsm6dsx_sensor_set_enable(sensor, enable);
+	case ST_LSM6DSX_ID_SF:
+		return st_lsm6dsx_sf_set_enable(sensor, enable);
+	default:
+		return st_lsm6dsx_sensor_set_enable(sensor, enable);
+	}
 }
 
 static const
diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
index 9db48e835d4f..a689c081c186 100644
--- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
+++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
@@ -88,6 +88,7 @@ enum st_lsm6dsx_fifo_tag {
 	ST_LSM6DSX_EXT0_TAG = 0x0f,
 	ST_LSM6DSX_EXT1_TAG = 0x10,
 	ST_LSM6DSX_EXT2_TAG = 0x11,
+	ST_LSM6DSX_ROT_TAG = 0x13,
 };
 
 static const
@@ -226,8 +227,11 @@ static int st_lsm6dsx_set_fifo_odr(struct st_lsm6dsx_sensor *sensor,
 	u8 data;
 
 	/* Only accel and gyro have batch registers. */
-	if (sensor->id >= ARRAY_SIZE(hw->settings->batch))
+	if (sensor->id >= ARRAY_SIZE(hw->settings->batch)) {
+		if (sensor->id == ST_LSM6DSX_ID_SF)
+			return st_lsm6dsx_sf_set_odr(sensor, enable);
 		return 0;
+	}
 	batch_reg = &hw->settings->batch[sensor->id];
 	if (batch_reg->addr) {
 		int val;
@@ -579,6 +583,16 @@ st_lsm6dsx_push_tagged_data(struct st_lsm6dsx_hw *hw, u8 tag,
 	case ST_LSM6DSX_EXT2_TAG:
 		iio_dev = hw->iio_devs[ST_LSM6DSX_ID_EXT2];
 		break;
+	case ST_LSM6DSX_ROT_TAG:
+		/**
+		 * The sensor reports only the {X, Y, Z} elements of the
+		 * quaternion vector; set the W value to 0 (it can be derived
+		 * from the {X, Y, Z} values due to the property that the vector
+		 * is normalized).
+		 */
+		*(u16 *)(data + ST_LSM6DSX_SAMPLE_SIZE) = 0;
+		iio_dev = hw->iio_devs[ST_LSM6DSX_ID_SF];
+		break;
 	default:
 		return -EINVAL;
 	}
diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
index dc0ae0e488ce..c21163a06a71 100644
--- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
+++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
@@ -94,6 +94,24 @@
 
 #define ST_LSM6DSX_REG_WHOAMI_ADDR		0x0f
 
+/* Raw values from the IMU are 16-bit half-precision floating-point numbers. */
+#define ST_LSM6DSX_CHANNEL_ROT						\
+{									\
+	.type = IIO_ROT,						\
+	.modified = 1,							\
+	.channel2 = IIO_MOD_QUATERNION,					\
+	.info_mask_shared_by_all = BIT(IIO_CHAN_INFO_SAMP_FREQ),	\
+	.scan_index = 0,						\
+	.scan_type = {							\
+		.sign = 'u',						\
+		.realbits = 16,						\
+		.storagebits = 16,					\
+		.endianness = IIO_LE,					\
+		.repeat = 4,						\
+	},								\
+	.ext_info = st_lsm6dsx_ext_info,				\
+}
+
 #define ST_LSM6DSX_TS_SENSITIVITY		25000UL /* 25us */
 
 static const struct iio_chan_spec st_lsm6dsx_acc_channels[] = {
@@ -153,6 +171,11 @@ static const struct iio_chan_spec st_lsm6ds0_gyro_channels[] = {
 	IIO_CHAN_SOFT_TIMESTAMP(3),
 };
 
+static const struct iio_chan_spec st_lsm6dsx_sf_channels[] = {
+	ST_LSM6DSX_CHANNEL_ROT,
+	IIO_CHAN_SOFT_TIMESTAMP(1),
+};
+
 static const struct st_lsm6dsx_settings st_lsm6dsx_sensor_settings[] = {
 	{
 		.reset = {
@@ -1492,6 +1515,35 @@ static const struct st_lsm6dsx_settings st_lsm6dsx_sensor_settings[] = {
 			.wakeup_src_y_mask = BIT(1),
 			.wakeup_src_x_mask = BIT(2),
 		},
+		.sf_settings = {
+			.chan = st_lsm6dsx_sf_channels,
+			.chan_len = ARRAY_SIZE(st_lsm6dsx_sf_channels),
+			.odr_table = {
+				.reg = {
+					.addr = 0x5e,
+					.mask = GENMASK(5, 3),
+				},
+				.odr_avl[0] = {  15000, 0x00 },
+				.odr_avl[1] = {  30000, 0x01 },
+				.odr_avl[2] = {  60000, 0x02 },
+				.odr_avl[3] = { 120000, 0x03 },
+				.odr_avl[4] = { 240000, 0x04 },
+				.odr_avl[5] = { 480000, 0x05 },
+				.odr_len = 6,
+			},
+			.fifo_enable = {
+				.addr = 0x44,
+				.mask = BIT(1),
+			},
+			.page_mux = {
+				.addr = 0x01,
+				.mask = BIT(7),
+			},
+			.enable = {
+				.addr = 0x04,
+				.mask = BIT(1),
+			},
+		},
 	},
 	{
 		.reset = {
@@ -2899,6 +2951,12 @@ int st_lsm6dsx_probe(struct device *dev, int irq, int hw_id,
 			return err;
 	}
 
+	if (hw->settings->sf_settings.chan) {
+		err = st_lsm6dsx_sf_probe(hw, name);
+		if (err)
+			return err;
+	}
+
 	if (hw->irq > 0) {
 		err = st_lsm6dsx_irq_setup(hw);
 		if (err < 0)
diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_fusion.c b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_fusion.c
new file mode 100644
index 000000000000..7c78f14cbb91
--- /dev/null
+++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_fusion.c
@@ -0,0 +1,224 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * STMicroelectronics st_lsm6dsx IMU sensor fusion
+ */
+
+#include <linux/iio/iio.h>
+#include <linux/iio/sysfs.h>
+#include <linux/mutex.h>
+#include <linux/regmap.h>
+#include <linux/sprintf.h>
+#include <linux/types.h>
+#include <linux/units.h>
+
+#include "st_lsm6dsx.h"
+
+static int
+st_lsm6dsx_sf_get_odr_val(const struct st_lsm6dsx_sf_settings *settings,
+			  u32 odr, u8 *val)
+{
+	int i;
+
+	for (i = 0; i < settings->odr_table.odr_len; i++) {
+		if (settings->odr_table.odr_avl[i].milli_hz == odr)
+			break;
+	}
+	if (i == settings->odr_table.odr_len)
+		return -EINVAL;
+
+	*val = settings->odr_table.odr_avl[i].val;
+	return 0;
+}
+
+/**
+ * st_lsm6dsx_sf_set_page - Enable or disable access to sensor fusion
+ * configuration registers.
+ * @hw: Sensor hardware instance.
+ * @enable: True to enable access, false to disable access.
+ *
+ * The register page lock is acquired when enabling access, and released when
+ * disabling access. Therefore, a function call with @enable set to true must be
+ * followed by a call with @enable set to false (unless the first call returns
+ * an error value).
+ *
+ * Return: 0 on success, negative value on error.
+ */
+static int st_lsm6dsx_sf_set_page(struct st_lsm6dsx_hw *hw, bool enable)
+{
+	const struct st_lsm6dsx_reg *mux;
+	int err;
+
+	mux = &hw->settings->sf_settings.page_mux;
+	if (enable)
+		mutex_lock(&hw->page_lock);
+	err = regmap_assign_bits(hw->regmap, mux->addr, mux->mask, enable);
+	if (!enable || err < 0)
+		mutex_unlock(&hw->page_lock);
+
+	return err;
+}
+
+int st_lsm6dsx_sf_set_enable(struct st_lsm6dsx_sensor *sensor, bool enable)
+{
+	struct st_lsm6dsx_hw *hw = sensor->hw;
+	const struct st_lsm6dsx_reg *enable_reg;
+	int err;
+
+	enable_reg = &hw->settings->sf_settings.enable;
+	err = st_lsm6dsx_sf_set_page(hw, true);
+	if (err < 0)
+		return err;
+
+	err = regmap_assign_bits(hw->regmap, enable_reg->addr, enable_reg->mask,
+				 enable);
+	st_lsm6dsx_sf_set_page(hw, false);
+
+	return err;
+}
+
+int st_lsm6dsx_sf_set_odr(struct st_lsm6dsx_sensor *sensor, bool enable)
+{
+	struct st_lsm6dsx_hw *hw = sensor->hw;
+	const struct st_lsm6dsx_sf_settings *settings;
+	u8 data;
+	int err;
+
+	err = st_lsm6dsx_sf_set_page(hw, true);
+	if (err < 0)
+		return err;
+
+	settings = &hw->settings->sf_settings;
+	if (enable) {
+		u8 odr_val;
+		const struct st_lsm6dsx_reg *reg = &settings->odr_table.reg;
+
+		st_lsm6dsx_sf_get_odr_val(settings, sensor->hwfifo_odr_mHz,
+					  &odr_val);
+		data = ST_LSM6DSX_SHIFT_VAL(odr_val, reg->mask);
+		err = regmap_update_bits(hw->regmap, reg->addr, reg->mask,
+					 data);
+		if (err < 0)
+			goto out;
+	}
+	err = regmap_assign_bits(hw->regmap, settings->fifo_enable.addr,
+				 settings->fifo_enable.mask, enable);
+
+out:
+	st_lsm6dsx_sf_set_page(hw, false);
+
+	return err;
+}
+
+static int st_lsm6dsx_sf_read_raw(struct iio_dev *iio_dev,
+				  struct iio_chan_spec const *ch,
+				  int *val, int *val2, long mask)
+{
+	struct st_lsm6dsx_sensor *sensor = iio_priv(iio_dev);
+
+	switch (mask) {
+	case IIO_CHAN_INFO_SAMP_FREQ:
+		*val = sensor->hwfifo_odr_mHz / MILLI;
+		*val2 = (sensor->hwfifo_odr_mHz % MILLI) * MILLI;
+		return IIO_VAL_INT_PLUS_MICRO;
+	default:
+		return -EINVAL;
+	}
+}
+
+static int st_lsm6dsx_sf_write_raw(struct iio_dev *iio_dev,
+				   struct iio_chan_spec const *chan,
+				   int val, int val2, long mask)
+{
+	struct st_lsm6dsx_sensor *sensor = iio_priv(iio_dev);
+	const struct st_lsm6dsx_sf_settings *settings;
+	int err;
+
+	settings = &sensor->hw->settings->sf_settings;
+	switch (mask) {
+	case IIO_CHAN_INFO_SAMP_FREQ: {
+		u32 odr_mHz;
+		u8 odr_val;
+
+		odr_mHz = val * MILLI + val2 / MILLI;
+		err = st_lsm6dsx_sf_get_odr_val(settings, odr_mHz, &odr_val);
+		if (err)
+			return err;
+
+		sensor->hwfifo_odr_mHz = odr_mHz;
+		break;
+	}
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static ssize_t st_lsm6dsx_sf_sampling_freq_avail(struct device *dev,
+						 struct device_attribute *attr,
+						 char *buf)
+{
+	struct st_lsm6dsx_sensor *sensor = iio_priv(dev_to_iio_dev(dev));
+	const struct st_lsm6dsx_sf_settings *settings;
+	int i, len = 0;
+
+	settings = &sensor->hw->settings->sf_settings;
+	for (i = 0; i < settings->odr_table.odr_len; i++) {
+		u32 val = settings->odr_table.odr_avl[i].milli_hz;
+
+		len += scnprintf(buf + len, PAGE_SIZE - len, "%lu.%03lu ",
+				 val / MILLI, val % MILLI);
+	}
+	buf[len - 1] = '\n';
+
+	return len;
+}
+
+static IIO_DEV_ATTR_SAMP_FREQ_AVAIL(st_lsm6dsx_sf_sampling_freq_avail);
+static struct attribute *st_lsm6dsx_sf_attributes[] = {
+	&iio_dev_attr_sampling_frequency_available.dev_attr.attr,
+	NULL,
+};
+
+static const struct attribute_group st_lsm6dsx_sf_attribute_group = {
+	.attrs = st_lsm6dsx_sf_attributes,
+};
+
+static const struct iio_info st_lsm6dsx_sf_info = {
+	.attrs = &st_lsm6dsx_sf_attribute_group,
+	.read_raw = st_lsm6dsx_sf_read_raw,
+	.write_raw = st_lsm6dsx_sf_write_raw,
+	.hwfifo_set_watermark = st_lsm6dsx_set_watermark,
+};
+
+int st_lsm6dsx_sf_probe(struct st_lsm6dsx_hw *hw, const char *name)
+{
+	const struct st_lsm6dsx_sf_settings *settings;
+	struct st_lsm6dsx_sensor *sensor;
+	struct iio_dev *iio_dev;
+
+	iio_dev = devm_iio_device_alloc(hw->dev, sizeof(*sensor));
+	if (!iio_dev)
+		return -ENOMEM;
+
+	settings = &hw->settings->sf_settings;
+	sensor = iio_priv(iio_dev);
+	sensor->id = ST_LSM6DSX_ID_SF;
+	sensor->hw = hw;
+	sensor->hwfifo_odr_mHz = settings->odr_table.odr_avl[0].milli_hz;
+	sensor->watermark = 1;
+	iio_dev->modes = INDIO_DIRECT_MODE;
+	iio_dev->info = &st_lsm6dsx_sf_info;
+	iio_dev->channels = settings->chan;
+	iio_dev->num_channels = settings->chan_len;
+	scnprintf(sensor->name, sizeof(sensor->name), "%s_sf", name);
+	iio_dev->name = sensor->name;
+
+	/**
+	 *  Put the IIO device pointer in the iio_devs array so that the caller
+	 *  can set up a buffer and register this IIO device.
+	 */
+	hw->iio_devs[ST_LSM6DSX_ID_SF] = iio_dev;
+
+	return 0;
+}
-- 
2.39.5

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