[PATCH v3 0/3] imu: st_lsm6dsx: Add support for rotation sensor

[PATCH v3 0/3] imu: st_lsm6dsx: Add support for rotation sensor

[Francesco Lavra]

This series adds support for the rotation sensor functionality present in
some chips from the ST LSM6DSX IMU family.
The second commit is a fix to a previous commit of mine [*] which made it
to 6.19-rcX; the fix technically changes userspace, but this should be OK
as long as it goes in during this release cycle.
Tested on LSM6DSV16X.

Changes from v2 [2]:
- amended description of patch 2 to point out that there are no supported
  gyro events (Jonathan)
- removed superfluous parentheses in st_lsm6dsx_fifo_setup (Lorenzo)
- added Lorenzo's acked-by tag to patch 3
- added missing checks of st_lsm6dsx_sf_set_page() return value (Jonathan)
- added comment in st_lsm6dsx_sf_write_raw (Jonathan)

Changes from v1 [1]:
- swapped patches 1 and 2 (Jonathan)
- miscellaneous stylistic changes (Andy)
- fixed usage of MICRO and MILLI constants in st_lsm6dsx_sf_read_raw and
  st_lsm6dsx_sf_write_raw (Andy)
- replaced scnprintf() with sysfs_emit_at() in
  st_lsm6dsx_sf_sampling_freq_avail (Andy)
- replaced scnprintf() with snprintf() in st_lsm6dsx_sf_probe (Andy)
- clarified in a comment in st_lsm6dsx_set_fifo_odr() that only internal
  sensors have a FIFO ODR configuration register (Jonathan)
- modified patch 3 description to explain justification for the extra IIO
  device (Jonathan)
- moved page lock from st_lsm6dsx_sf_set_page() to the callers (Jonathan)
- s/magnetometer/gyroscope/ in patch 2 description

[*] https://lore.kernel.org/linux-iio/20251017164255.1251060-3-flavra@baylibre.com/
[1] https://lore.kernel.org/linux-iio/20260109181528.154127-1-flavra@baylibre.com/T/
[2] https://lore.kernel.org/linux-iio/20260115122431.1014630-1-flavra@baylibre.com/T/

Francesco Lavra (3):
  iio: imu: st_lsm6dsx: set FIFO ODR for accelerometer and gyroscope
    only
  iio: imu: st_lsm6dsx: set buffer sampling frequency for accelerometer
    only
  iio: imu: st_lsm6dsx: add support for rotation sensor

 drivers/iio/imu/st_lsm6dsx/Makefile           |   2 +-
 drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h       |  26 ++-
 .../iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c    |  29 ++-
 drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c  |  58 +++++
 .../iio/imu/st_lsm6dsx/st_lsm6dsx_fusion.c    | 220 ++++++++++++++++++
 5 files changed, 328 insertions(+), 7 deletions(-)
 create mode 100644 drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_fusion.c

-- 
2.39.5

[PATCH v3 1/3] iio: imu: st_lsm6dsx: set FIFO ODR for accelerometer and gyroscope only

[Francesco Lavra]

The st_lsm6dsx_set_fifo_odr() function, which is called when enabling and
disabling the hardware FIFO, checks the contents of the hw->settings->batch
array at index sensor->id, and then sets the current ODR value in sensor
registers that depend on whether the register address is set in the above
array element. This logic is valid for internal sensors only, i.e. the
accelerometer and gyroscope; however, since commit c91c1c844ebd ("iio: imu:
st_lsm6dsx: add i2c embedded controller support"), this function is called
also when configuring the hardware FIFO for external sensors (i.e. sensors
accessed through the sensor hub functionality), which can result in
unrelated device registers being written.

Add a check to the beginning of st_lsm6dsx_set_fifo_odr() so that it does
not touch any registers unless it is called for internal sensors.

Fixes: c91c1c844ebd ("iio: imu: st_lsm6dsx: add i2c embedded controller support")
Signed-off-by: Francesco Lavra <flavra@baylibre.com>
---
 drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
index 55d877745575..1ee2fc5f5f1f 100644
--- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
+++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
@@ -225,6 +225,10 @@ static int st_lsm6dsx_set_fifo_odr(struct st_lsm6dsx_sensor *sensor,
 	const struct st_lsm6dsx_reg *batch_reg;
 	u8 data;
 
+	/* Only internal sensors have a FIFO ODR configuration register. */
+	if (sensor->id >= ARRAY_SIZE(hw->settings->batch))
+		return 0;
+
 	batch_reg = &hw->settings->batch[sensor->id];
 	if (batch_reg->addr) {
 		int val;
-- 
2.39.5

[PATCH v3 2/3] iio: imu: st_lsm6dsx: set buffer sampling frequency for accelerometer only

[Francesco Lavra]

The st_lsm6dsx_hwfifo_odr_store() function, which is called when userspace
writes the buffer sampling frequency sysfs attribute, calls
st_lsm6dsx_check_odr(), which accesses the odr_table array at index
`sensor->id`; since this array is only 2 entries long, an access for any
sensor type other than accelerometer or gyroscope is an out-of-bounds
access.

The motivation for being able to set a buffer frequency different from the
sensor sampling frequency is to support use cases that need accurate event
detection (which requires a high sampling frequency) while retrieving
sensor data at low frequency. Since all the supported event types are
generated from acceleration data only, do not create the buffer sampling
frequency attribute for sensor types other than the accelerometer.

Fixes: 6b648a36c200 ("iio: imu: st_lsm6dsx: Decouple sensor ODR from FIFO batch data rate")
Signed-off-by: Francesco Lavra <flavra@baylibre.com>
---
 drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
index 1ee2fc5f5f1f..5b28a3ffcc3d 100644
--- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
+++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
@@ -862,12 +862,21 @@ int st_lsm6dsx_fifo_setup(struct st_lsm6dsx_hw *hw)
 	int i, ret;
 
 	for (i = 0; i < ST_LSM6DSX_ID_MAX; i++) {
+		const struct iio_dev_attr **attrs;
+
 		if (!hw->iio_devs[i])
 			continue;
 
+		/*
+		 * For the accelerometer, allow setting FIFO sampling frequency
+		 * values different from the sensor sampling frequency, which
+		 * may be needed to keep FIFO data rate low while sampling
+		 * acceleration data at high rates for accurate event detection.
+		 */
+		attrs = i == ST_LSM6DSX_ID_ACC ? st_lsm6dsx_buffer_attrs : NULL;
 		ret = devm_iio_kfifo_buffer_setup_ext(hw->dev, hw->iio_devs[i],
 						      &st_lsm6dsx_buffer_ops,
-						      st_lsm6dsx_buffer_attrs);
+						      attrs);
 		if (ret)
 			return ret;
 	}
-- 
2.39.5

[PATCH v3 3/3] iio: imu: st_lsm6dsx: add support for rotation sensor

[Francesco Lavra]

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 the rate at which sensor fusion data is
generated may not match the data rate from any of the existing devices.

Tested on LSMDSV16X.

Signed-off-by: Francesco Lavra <flavra@baylibre.com>
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
---
 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    | 220 ++++++++++++++++++
 5 files changed, 315 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_fifo_mode {
@@ -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 5b28a3ffcc3d..9a259e04755f 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 internal sensors have a FIFO ODR configuration register. */
-	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) {
@@ -580,6 +584,16 @@ 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,				\
+}
+
 static const struct iio_event_spec st_lsm6dsx_ev_motion[] = {
 	{
 		.type = IIO_EV_TYPE_THRESH,
@@ -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[] = {
 				},
 			},
 		},
+		.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..11ab246ef9d6
--- /dev/null
+++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_fusion.c
@@ -0,0 +1,220 @@
+// 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.
+ *
+ * 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 = &hw->settings->sf_settings.page_mux;
+
+	return regmap_assign_bits(hw->regmap, mux->addr, mux->mask, enable);
+}
+
+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 *en_reg;
+	int err;
+
+	guard(mutex)(&hw->page_lock);
+
+	en_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, en_reg->addr, en_reg->mask, enable);
+	if (err < 0) {
+		st_lsm6dsx_sf_set_page(hw, false);
+		return err;
+	}
+
+	return st_lsm6dsx_sf_set_page(hw, false);
+}
+
+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;
+
+	guard(mutex)(&hw->page_lock);
+
+	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);
+	if (err < 0)
+		goto out;
+
+	return st_lsm6dsx_sf_set_page(hw, false);
+
+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) * (MICRO / 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 = val * MILLI + val2 * MILLI / MICRO;
+		u8 odr_val;
+
+		/* check that the requested frequency is supported */
+		err = st_lsm6dsx_sf_get_odr_val(settings, odr_mHz, &odr_val);
+		if (err)
+			return err;
+
+		sensor->hwfifo_odr_mHz = odr_mHz;
+		return 0;
+	}
+	default:
+		return -EINVAL;
+	}
+}
+
+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 len = 0;
+
+	settings = &sensor->hw->settings->sf_settings;
+	for (unsigned int i = 0; i < settings->odr_table.odr_len; i++) {
+		u32 val = settings->odr_table.odr_avl[i].milli_hz;
+
+		len += sysfs_emit_at(buf, 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;
+	snprintf(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

Re: [PATCH v3 3/3] iio: imu: st_lsm6dsx: add support for rotation sensor

[Andy Shevchenko]

On Mon, Jan 19, 2026 at 11:04:49AM +0100, Francesco Lavra wrote:
> 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 the rate at which sensor fusion data is
> generated may not match the data rate from any of the existing devices.
> 
> Tested on LSMDSV16X.

...

> 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;

This looks confusing taking into account

	s16 val = le16_to_cpu(*(__le16 *)data);

(which actually should use le16_to_cpup() instead of the direct conversion).

> +		iio_dev = hw->iio_devs[ST_LSM6DSX_ID_SF];
> +		break;
>  	default:
>  		return -EINVAL;
>  	}

...

> +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 *en_reg;
> +	int err;
> +
> +	guard(mutex)(&hw->page_lock);
> +
> +	en_reg = &hw->settings->sf_settings.enable;
> +	err = st_lsm6dsx_sf_set_page(hw, true);
> +	if (err < 0)

Do you need ' < 0' here? Why isn't it required at the end of the function?

> +		return err;
> +
> +	err = regmap_assign_bits(hw->regmap, en_reg->addr, en_reg->mask, enable);
> +	if (err < 0) {

' < 0' is not needed.

> +		st_lsm6dsx_sf_set_page(hw, false);
> +		return err;
> +	}
> +
> +	return st_lsm6dsx_sf_set_page(hw, false);
> +}

And IIRC I replied that these _sf_set_page() seems to be used only with
the explicit boolean value, which means a good hint that it needs to be
split just to two functions doing for true and false. It will increase
the readability of the code in both places (in the caller and callee).

...

> +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;
> +
> +	guard(mutex)(&hw->page_lock);
> +
> +	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;

Can we use reversed xmas tree ordering?

> +		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);
> +	if (err < 0)
> +		goto out;
> +
> +	return st_lsm6dsx_sf_set_page(hw, false);
> +
> +out:
> +	st_lsm6dsx_sf_set_page(hw, false);
> +
> +	return err;
> +}

...

> +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 = val * MILLI + val2 * MILLI / MICRO;

Probably "(MILLI / MICRO)" (with parentheses) to avoid potential overflows,

> +		u8 odr_val;
> +
> +		/* check that the requested frequency is supported */
> +		err = st_lsm6dsx_sf_get_odr_val(settings, odr_mHz, &odr_val);
> +		if (err)
> +			return err;
> +
> +		sensor->hwfifo_odr_mHz = odr_mHz;
> +		return 0;
> +	}
> +	default:
> +		return -EINVAL;
> +	}
> +}

...

> +	snprintf(sensor->name, sizeof(sensor->name), "%s_sf", name);

Does GCC complain on this (`make W=1` build)?
Since this can cut the string and we don't check the return value, the Q is:
is this okay to have a reduced string?

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v3 3/3] iio: imu: st_lsm6dsx: add support for rotation sensor

[Dan Carpenter]

Hi Francesco,

kernel test robot noticed the following build warnings:

https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Francesco-Lavra/iio-imu-st_lsm6dsx-set-FIFO-ODR-for-accelerometer-and-gyroscope-only/20260119-181615
base:   https://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio.git togreg
patch link:    https://lore.kernel.org/r/20260119100449.1559624-4-flavra%40baylibre.com
patch subject: [PATCH v3 3/3] iio: imu: st_lsm6dsx: add support for rotation sensor
config: sparc-randconfig-r071-20260119 (https://download.01.org/0day-ci/archive/20260120/202601200451.4BeA8JAe-lkp@intel.com/config)
compiler: sparc-linux-gcc (GCC) 15.2.0
smatch version: v0.5.0-8985-g2614ff1a

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
| Closes: https://lore.kernel.org/r/202601200451.4BeA8JAe-lkp@intel.com/

smatch warnings:
drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_fusion.c:90 st_lsm6dsx_sf_set_odr() error: uninitialized symbol 'odr_val'.

vim +/odr_val +90 drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_fusion.c

aa03865dcb5ed7 Francesco Lavra 2026-01-19   70  int st_lsm6dsx_sf_set_odr(struct st_lsm6dsx_sensor *sensor, bool enable)
aa03865dcb5ed7 Francesco Lavra 2026-01-19   71  {
aa03865dcb5ed7 Francesco Lavra 2026-01-19   72  	struct st_lsm6dsx_hw *hw = sensor->hw;
aa03865dcb5ed7 Francesco Lavra 2026-01-19   73  	const struct st_lsm6dsx_sf_settings *settings;
aa03865dcb5ed7 Francesco Lavra 2026-01-19   74  	u8 data;
aa03865dcb5ed7 Francesco Lavra 2026-01-19   75  	int err;
aa03865dcb5ed7 Francesco Lavra 2026-01-19   76  
aa03865dcb5ed7 Francesco Lavra 2026-01-19   77  	guard(mutex)(&hw->page_lock);
aa03865dcb5ed7 Francesco Lavra 2026-01-19   78  
aa03865dcb5ed7 Francesco Lavra 2026-01-19   79  	err = st_lsm6dsx_sf_set_page(hw, true);
aa03865dcb5ed7 Francesco Lavra 2026-01-19   80  	if (err < 0)
aa03865dcb5ed7 Francesco Lavra 2026-01-19   81  		return err;
aa03865dcb5ed7 Francesco Lavra 2026-01-19   82  
aa03865dcb5ed7 Francesco Lavra 2026-01-19   83  	settings = &hw->settings->sf_settings;
aa03865dcb5ed7 Francesco Lavra 2026-01-19   84  	if (enable) {
aa03865dcb5ed7 Francesco Lavra 2026-01-19   85  		u8 odr_val;
aa03865dcb5ed7 Francesco Lavra 2026-01-19   86  		const struct st_lsm6dsx_reg *reg = &settings->odr_table.reg;
aa03865dcb5ed7 Francesco Lavra 2026-01-19   87  
aa03865dcb5ed7 Francesco Lavra 2026-01-19   88  		st_lsm6dsx_sf_get_odr_val(settings, sensor->hwfifo_odr_mHz,
aa03865dcb5ed7 Francesco Lavra 2026-01-19   89  					  &odr_val);

No error checking on st_lsm6dsx_sf_get_odr_val().  Probably this is
deliberate?

aa03865dcb5ed7 Francesco Lavra 2026-01-19  @90  		data = ST_LSM6DSX_SHIFT_VAL(odr_val, reg->mask);
aa03865dcb5ed7 Francesco Lavra 2026-01-19   91  		err = regmap_update_bits(hw->regmap, reg->addr, reg->mask,
aa03865dcb5ed7 Francesco Lavra 2026-01-19   92  					 data);
aa03865dcb5ed7 Francesco Lavra 2026-01-19   93  		if (err < 0)
aa03865dcb5ed7 Francesco Lavra 2026-01-19   94  			goto out;
aa03865dcb5ed7 Francesco Lavra 2026-01-19   95  	}
aa03865dcb5ed7 Francesco Lavra 2026-01-19   96  
aa03865dcb5ed7 Francesco Lavra 2026-01-19   97  	err = regmap_assign_bits(hw->regmap, settings->fifo_enable.addr,
aa03865dcb5ed7 Francesco Lavra 2026-01-19   98  				 settings->fifo_enable.mask, enable);
aa03865dcb5ed7 Francesco Lavra 2026-01-19   99  	if (err < 0)
aa03865dcb5ed7 Francesco Lavra 2026-01-19  100  		goto out;
aa03865dcb5ed7 Francesco Lavra 2026-01-19  101  
aa03865dcb5ed7 Francesco Lavra 2026-01-19  102  	return st_lsm6dsx_sf_set_page(hw, false);
aa03865dcb5ed7 Francesco Lavra 2026-01-19  103  
aa03865dcb5ed7 Francesco Lavra 2026-01-19  104  out:
aa03865dcb5ed7 Francesco Lavra 2026-01-19  105  	st_lsm6dsx_sf_set_page(hw, false);
aa03865dcb5ed7 Francesco Lavra 2026-01-19  106  
aa03865dcb5ed7 Francesco Lavra 2026-01-19  107  	return err;
aa03865dcb5ed7 Francesco Lavra 2026-01-19  108  }

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH v3 3/3] iio: imu: st_lsm6dsx: add support for rotation sensor

[Francesco Lavra]

[-- Attachment #1: Type: text/plain, Size: 4732 bytes --]

On Mon, 2026-01-19 at 12:33 +0200, Andy Shevchenko wrote:
> On Mon, Jan 19, 2026 at 11:04:49AM +0100, Francesco Lavra wrote:
> > 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 the rate at which sensor fusion data is
> > generated may not match the data rate from any of the existing devices.
> > 
> > Tested on LSMDSV16X.
> 
> ...
> 
> > 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;
> 
> This looks confusing taking into account
> 
>         s16 val = le16_to_cpu(*(__le16 *)data);
> 
> (which actually should use le16_to_cpup() instead of the direct
> conversion).

The above val variable is used to do a (val >= ST_LSM6DSX_INVALID_SAMPLE)
check, which actually should be done only if (tag == ST_LSM6DSX_ACC_TAG ||
tag == ST_LSM6DSX_GYRO_TAG).
I will add a patch to fix this (it will fix commit 960506ed2c69 "iio: imu:
st_lsm6dsx: enable drdy-mask if available")

> > +               iio_dev = hw->iio_devs[ST_LSM6DSX_ID_SF];
> > +               break;
> >         default:
> >                 return -EINVAL;
> >         }
> 
> ...
> 
> > +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 *en_reg;
> > +       int err;
> > +
> > +       guard(mutex)(&hw->page_lock);
> > +
> > +       en_reg = &hw->settings->sf_settings.enable;
> > +       err = st_lsm6dsx_sf_set_page(hw, true);
> > +       if (err < 0)
> 
> Do you need ' < 0' here? Why isn't it required at the end of the
> function?

Will drop ' < 0'

> > +               return err;
> > +
> > +       err = regmap_assign_bits(hw->regmap, en_reg->addr, en_reg-
> > >mask, enable);
> > +       if (err < 0) {
> 
>  is not needed.
> 
> > +               st_lsm6dsx_sf_set_page(hw, false);
> > +               return err;
> > +       }
> > +
> > +       return st_lsm6dsx_sf_set_page(hw, false);
> > +}
> 
> And IIRC I replied that these _sf_set_page() seems to be used only with
> the explicit boolean value, which means a good hint that it needs to be
> split just to two functions doing for true and false. It will increase
> the readability of the code in both places (in the caller and callee).

OK

> ...
> 
> > +       snprintf(sensor->name, sizeof(sensor->name), "%s_sf", name);
> 
> Does GCC complain on this (`make W=1` build)?
> Since this can cut the string and we don't check the return value, the Q
> is:
> is this okay to have a reduced string?

gcc does not complain with W=1. sensor->name is appropriately sized to
accommodate the longest possible name; if it wasn't, the string would be
cut in the accel and gyro IIO devices too (which use a longer suffix than
"_sf").


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Re: [PATCH v3 3/3] iio: imu: st_lsm6dsx: add support for rotation sensor

[Andy Shevchenko]

On Tue, Jan 20, 2026 at 10:28:15AM +0100, Francesco Lavra wrote:
> On Mon, 2026-01-19 at 12:33 +0200, Andy Shevchenko wrote:
> > On Mon, Jan 19, 2026 at 11:04:49AM +0100, Francesco Lavra wrote:

...

> > > +       snprintf(sensor->name, sizeof(sensor->name), "%s_sf", name);
> > 
> > Does GCC complain on this (`make W=1` build)?
> > Since this can cut the string and we don't check the return value, the Q
> > is:
> > is this okay to have a reduced string?
> 
> gcc does not complain with W=1. sensor->name is appropriately sized to
> accommodate the longest possible name; if it wasn't, the string would be
> cut in the accel and gyro IIO devices too (which use a longer suffix than
> "_sf").

Right, the question is if compiler can prove that or not.

We have several patches in input subsystem to hide the warning by switching
to scnprintf(), which I consider not the best approach, but still it depends
if we care about cut or not. If we do, we should check for overflow.

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v3 3/3] iio: imu: st_lsm6dsx: add support for rotation sensor

[Francesco Lavra]

[-- Attachment #1: Type: text/plain, Size: 1395 bytes --]

On Tue, 2026-01-20 at 11:36 +0200, Andy Shevchenko wrote:
> On Tue, Jan 20, 2026 at 10:28:15AM +0100, Francesco Lavra wrote:
> > On Mon, 2026-01-19 at 12:33 +0200, Andy Shevchenko wrote:
> > > On Mon, Jan 19, 2026 at 11:04:49AM +0100, Francesco Lavra wrote:
> 
> ...
> 
> > > > +       snprintf(sensor->name, sizeof(sensor->name), "%s_sf",
> > > > name);
> > > 
> > > Does GCC complain on this (`make W=1` build)?
> > > Since this can cut the string and we don't check the return value,
> > > the Q
> > > is:
> > > is this okay to have a reduced string?
> > 
> > gcc does not complain with W=1. sensor->name is appropriately sized to
> > accommodate the longest possible name; if it wasn't, the string would
> > be
> > cut in the accel and gyro IIO devices too (which use a longer suffix
> > than
> > "_sf").
> 
> Right, the question is if compiler can prove that or not.
> 
> We have several patches in input subsystem to hide the warning by
> switching
> to scnprintf(), which I consider not the best approach, but still it
> depends
> if we care about cut or not. If we do, we should check for overflow.

A truncated string would result in a corrupted value in
/sys/bus/iio/devices/iio:deviceX/name, so I would say we do care if it's
truncated. But I think the most appropriate check we could add in the code
is a BUG_ON(); would that be acceptable?

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Re: [PATCH v3 3/3] iio: imu: st_lsm6dsx: add support for rotation sensor

[Andy Shevchenko]

On Tue, Jan 20, 2026 at 12:03 PM Francesco Lavra <flavra@baylibre.com> wrote:
> On Tue, 2026-01-20 at 11:36 +0200, Andy Shevchenko wrote:
> > On Tue, Jan 20, 2026 at 10:28:15AM +0100, Francesco Lavra wrote:
> > > On Mon, 2026-01-19 at 12:33 +0200, Andy Shevchenko wrote:
> > > > On Mon, Jan 19, 2026 at 11:04:49AM +0100, Francesco Lavra wrote:

...

> > > > > +       snprintf(sensor->name, sizeof(sensor->name), "%s_sf",
> > > > > name);
> > > >
> > > > Does GCC complain on this (`make W=1` build)?
> > > > Since this can cut the string and we don't check the return value,
> > > > the Q
> > > > is:
> > > > is this okay to have a reduced string?
> > >
> > > gcc does not complain with W=1. sensor->name is appropriately sized to
> > > accommodate the longest possible name; if it wasn't, the string would
> > > be
> > > cut in the accel and gyro IIO devices too (which use a longer suffix
> > > than
> > > "_sf").
> >
> > Right, the question is if compiler can prove that or not.
> >
> > We have several patches in input subsystem to hide the warning by
> > switching
> > to scnprintf(), which I consider not the best approach, but still it
> > depends
> > if we care about cut or not. If we do, we should check for overflow.
>
> A truncated string would result in a corrupted value in
> /sys/bus/iio/devices/iio:deviceX/name, so I would say we do care if it's
> truncated. But I think the most appropriate check we could add in the code
> is a BUG_ON(); would that be acceptable?

No. BUG_ON() == panic == reboot (with "reboot_on_panic" or so). Mere
drivers like this one should (almost) never use BUG() nor WARN(). Just
add an appropriate check.

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v3 3/3] iio: imu: st_lsm6dsx: add support for rotation sensor

[Francesco Lavra]

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On Tue, 2026-01-20 at 12:25 +0200, Andy Shevchenko wrote:
> On Tue, Jan 20, 2026 at 12:03 PM Francesco Lavra <flavra@baylibre.com>
> wrote:
> > On Tue, 2026-01-20 at 11:36 +0200, Andy Shevchenko wrote:
> > > On Tue, Jan 20, 2026 at 10:28:15AM +0100, Francesco Lavra wrote:
> > > > On Mon, 2026-01-19 at 12:33 +0200, Andy Shevchenko wrote:
> > > > > On Mon, Jan 19, 2026 at 11:04:49AM +0100, Francesco Lavra wrote:
> 
> ...
> 
> > > > > > +       snprintf(sensor->name, sizeof(sensor->name), "%s_sf",
> > > > > > name);
> > > > > 
> > > > > Does GCC complain on this (`make W=1` build)?
> > > > > Since this can cut the string and we don't check the return
> > > > > value,
> > > > > the Q
> > > > > is:
> > > > > is this okay to have a reduced string?
> > > > 
> > > > gcc does not complain with W=1. sensor->name is appropriately sized
> > > > to
> > > > accommodate the longest possible name; if it wasn't, the string
> > > > would
> > > > be
> > > > cut in the accel and gyro IIO devices too (which use a longer
> > > > suffix
> > > > than
> > > > "_sf").
> > > 
> > > Right, the question is if compiler can prove that or not.
> > > 
> > > We have several patches in input subsystem to hide the warning by
> > > switching
> > > to scnprintf(), which I consider not the best approach, but still it
> > > depends
> > > if we care about cut or not. If we do, we should check for overflow.
> > 
> > A truncated string would result in a corrupted value in
> > /sys/bus/iio/devices/iio:deviceX/name, so I would say we do care if
> > it's
> > truncated. But I think the most appropriate check we could add in the
> > code
> > is a BUG_ON(); would that be acceptable?
> 
> No. BUG_ON() == panic == reboot (with "reboot_on_panic" or so). Mere
> drivers like this one should (almost) never use BUG() nor WARN(). Just
> add an appropriate check.

I'm struggling to find a suitable error code to be returned in case of
failure. What do you suggest? -ENOSPC? -EOVERFLOW?

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Re: [PATCH v3 3/3] iio: imu: st_lsm6dsx: add support for rotation sensor

[Andy Shevchenko]

On Tue, Jan 20, 2026 at 2:23 PM Francesco Lavra <flavra@baylibre.com> wrote:
> On Tue, 2026-01-20 at 12:25 +0200, Andy Shevchenko wrote:
> > On Tue, Jan 20, 2026 at 12:03 PM Francesco Lavra <flavra@baylibre.com>
> > wrote:
> > > On Tue, 2026-01-20 at 11:36 +0200, Andy Shevchenko wrote:
> > > > On Tue, Jan 20, 2026 at 10:28:15AM +0100, Francesco Lavra wrote:
> > > > > On Mon, 2026-01-19 at 12:33 +0200, Andy Shevchenko wrote:
> > > > > > On Mon, Jan 19, 2026 at 11:04:49AM +0100, Francesco Lavra wrote:

...

> > > > > > > +       snprintf(sensor->name, sizeof(sensor->name), "%s_sf",
> > > > > > > name);
> > > > > >
> > > > > > Does GCC complain on this (`make W=1` build)?
> > > > > > Since this can cut the string and we don't check the return
> > > > > > value,
> > > > > > the Q
> > > > > > is:
> > > > > > is this okay to have a reduced string?
> > > > >
> > > > > gcc does not complain with W=1. sensor->name is appropriately sized
> > > > > to
> > > > > accommodate the longest possible name; if it wasn't, the string
> > > > > would
> > > > > be
> > > > > cut in the accel and gyro IIO devices too (which use a longer
> > > > > suffix
> > > > > than
> > > > > "_sf").
> > > >
> > > > Right, the question is if compiler can prove that or not.
> > > >
> > > > We have several patches in input subsystem to hide the warning by
> > > > switching
> > > > to scnprintf(), which I consider not the best approach, but still it
> > > > depends
> > > > if we care about cut or not. If we do, we should check for overflow.
> > >
> > > A truncated string would result in a corrupted value in
> > > /sys/bus/iio/devices/iio:deviceX/name, so I would say we do care if
> > > it's
> > > truncated. But I think the most appropriate check we could add in the
> > > code
> > > is a BUG_ON(); would that be acceptable?
> >
> > No. BUG_ON() == panic == reboot (with "reboot_on_panic" or so). Mere
> > drivers like this one should (almost) never use BUG() nor WARN(). Just
> > add an appropriate check.
>
> I'm struggling to find a suitable error code to be returned in case of
> failure. What do you suggest? -ENOSPC? -EOVERFLOW?

Same as strscpy() returns, IIRC -E2BIG.

-- 
With Best Regards,
Andy Shevchenko