[PATCH v3 0/2] iio: imu: st_lsm6dsx: Decouple sensor ODR from FIFO batch data rate

[PATCH v3 0/2] iio: imu: st_lsm6dsx: Decouple sensor ODR from FIFO batch data rate

[Francesco Lavra]

The rate at which accelerometer or gyroscope sensor samples are fed
to the hardware FIFO (batch data rate, or BDR) does not have to
coincide with the sensor sampling frequency (output data rate, or
ODR); the only requirement is for the BDR to not be greater than
the ODR. Having a BDR lower than the ODR is useful in cases where
an application requires a high sampling rate for accurate detection
of motion events (e.g. wakeup events), but wants to read sensor
sample values from the device buffer at a lower data rate (e.g. to
minimize the amount of I2C or SPI traffic and the rate of periodic
interrupts).
This change set amends the st_lsm6dsx IIO driver to support the above
use case. The first commit is a trivial fix to the source code comment
that indicates what measurement unit is used for the `odr` field of
struct st_lsm6ds_sensor, while the second commit introduces a new
`hwfifo_odr_mHz` field in the same struct to implement the new functionality.

Changes from v2 [2]:
 - fixed Fixes tag in patch 1/2
 - removed local variable from st_lsm6dsx_hwfifo_odr_show() (Lorenzo)
 - replaced multi-assignments with on assignment per line (Lorenzo)
 - added Acked-by tags to patches 1/2 and 2/2 (Lorenzo)

Changes from v1 [1]:
 - added Fixes tag to patch 1/2 (Lorenzo)
 - in sysfs store handler, moved iio_device_claim_direct() call to beginning
   of function (Lorenzo)
 - changed new struct st_lsm6dsx_sensor field name from `bdr` to
   `hwfifo_odr_mHz` (Lorenzo, David)
 - replaced min_t() and max_t() calls with min() and max() (Andy)
 - added setting of buffer frequency equal to main frequency whenever the
   latter is updated via sysfs (Jonathan)
 - miscellaneous stylistic modifications (Lorenzo, Andy, Jonathan)

[1] https://lore.kernel.org/linux-iio/20251009173609.992452-1-flavra@baylibre.com/T/#u
[2] https://lore.kernel.org/linux-iio/20251016172122.1220332-1-flavra@baylibre.com/T/#u

Francesco Lavra (2):
  iio: imu: st_lsm6dsx: Fix measurement unit for odr struct member
  iio: imu: st_lsm6dsx: Decouple sensor ODR from FIFO batch data rate

 drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h       |  4 +-
 .../iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c    | 71 ++++++++++++++++---
 drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c  |  7 +-
 drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_shub.c  |  2 +
 4 files changed, 73 insertions(+), 11 deletions(-)

-- 
2.39.5

[PATCH v3 1/2] iio: imu: st_lsm6dsx: Fix measurement unit for odr struct member

[Francesco Lavra]

The `odr` field in struct st_lsm6dsx_sensor contains a data rate
value expressed in mHz, not in Hz.

Fixes: f8710f0357bc3 ("iio: imu: st_lsm6dsx: express odr in mHZ")
Signed-off-by: Francesco Lavra <flavra@baylibre.com>
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
---
 drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h
index c225b246c8a5..bd366c6e282a 100644
--- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h
+++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h
@@ -365,7 +365,7 @@ enum st_lsm6dsx_fifo_mode {
  * @id: Sensor identifier.
  * @hw: Pointer to instance of struct st_lsm6dsx_hw.
  * @gain: Configured sensor sensitivity.
- * @odr: Output data rate of the sensor [Hz].
+ * @odr: Output data rate of the sensor [mHz].
  * @samples_to_discard: Number of samples to discard for filters settling time.
  * @watermark: Sensor watermark level.
  * @decimator: Sensor decimation factor.
-- 
2.39.5

[PATCH v3 2/2] iio: imu: st_lsm6dsx: Decouple sensor ODR from FIFO batch data rate

[Francesco Lavra]

The rate at which accelerometer or gyroscope sensor samples are fed
to the hardware FIFO (batch data rate, or BDR) does not have to
coincide with the sensor sampling frequency (output data rate, or
ODR); the only requirement is for the BDR to not be greater than
the ODR. Having a BDR lower than the ODR is useful in cases where
an application requires a high sampling rate for accurate detection
of motion events (e.g. wakeup events), but wants to read sensor
sample values from the hardware FIFO at a lower data rate (e.g. to
minimize the amount of I2C or SPI traffic and the rate of periodic
interrupts).
To support the above use case, add a sampling_frequency sysfs
attribute to the buffer directory of st_lsm6dsx IIO devices, which
controls the BDR for a given sensor independently from the "main"
sampling_frequency attribute (which controls the ODR); introduce a
new `hwfifo_odr_mHz` field in struct st_lsm6dsx_sensor to keep
track of the current BDR value, and use this field instead of the
`odr` field in the code that deals with the FIFO data rate. In the
sensor hub driver, make the hwfifo_odr_mHz value always mirror the
odr value, since there is no separate configuration setting to
control the BDR for data produced by the sensor hub functionality.
For backwards compatibility, set the buffer frequency equal to the
main frequency whenever the latter is updated via sysfs; if
userspace wants a different buffer frequency, it has to write to
the relevant sysfs attribute after any writes to the main frequency
attribute.

Signed-off-by: Francesco Lavra <flavra@baylibre.com>
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
---
 drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h       |  2 +
 .../iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c    | 71 ++++++++++++++++---
 drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c  |  7 +-
 drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_shub.c  |  2 +
 4 files changed, 72 insertions(+), 10 deletions(-)

diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h
index bd366c6e282a..3cd520bdec46 100644
--- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h
+++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h
@@ -366,6 +366,7 @@ enum st_lsm6dsx_fifo_mode {
  * @hw: Pointer to instance of struct st_lsm6dsx_hw.
  * @gain: Configured sensor sensitivity.
  * @odr: Output data rate of the sensor [mHz].
+ * hwfifo_odr_mHz: Batch data rate for hardware FIFO [mHz]
  * @samples_to_discard: Number of samples to discard for filters settling time.
  * @watermark: Sensor watermark level.
  * @decimator: Sensor decimation factor.
@@ -380,6 +381,7 @@ struct st_lsm6dsx_sensor {
 
 	u32 gain;
 	u32 odr;
+	u32 hwfifo_odr_mHz;
 
 	u16 samples_to_discard;
 	u16 watermark;
diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
index 8a9d2593576a..55d877745575 100644
--- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
+++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
@@ -56,6 +56,7 @@
 #include <linux/iio/kfifo_buf.h>
 #include <linux/iio/iio.h>
 #include <linux/iio/buffer.h>
+#include <linux/iio/sysfs.h>
 #include <linux/regmap.h>
 #include <linux/bitfield.h>
 
@@ -105,7 +106,7 @@ static int
 st_lsm6dsx_get_decimator_val(struct st_lsm6dsx_sensor *sensor, u32 max_odr)
 {
 	const int max_size = ARRAY_SIZE(st_lsm6dsx_decimator_table);
-	u32 decimator =  max_odr / sensor->odr;
+	u32 decimator = max_odr / sensor->hwfifo_odr_mHz;
 	int i;
 
 	if (decimator > 1)
@@ -136,14 +137,14 @@ static void st_lsm6dsx_get_max_min_odr(struct st_lsm6dsx_hw *hw,
 		if (!(hw->enable_mask & BIT(sensor->id)))
 			continue;
 
-		*max_odr = max_t(u32, *max_odr, sensor->odr);
-		*min_odr = min_t(u32, *min_odr, sensor->odr);
+		*max_odr = max(*max_odr, sensor->hwfifo_odr_mHz);
+		*min_odr = min(*min_odr, sensor->hwfifo_odr_mHz);
 	}
 }
 
 static u8 st_lsm6dsx_get_sip(struct st_lsm6dsx_sensor *sensor, u32 min_odr)
 {
-	u8 sip = sensor->odr / min_odr;
+	u8 sip = sensor->hwfifo_odr_mHz / min_odr;
 
 	return sip > 1 ? round_down(sip, 2) : sip;
 }
@@ -231,7 +232,7 @@ static int st_lsm6dsx_set_fifo_odr(struct st_lsm6dsx_sensor *sensor,
 		if (enable) {
 			int err;
 
-			err = st_lsm6dsx_check_odr(sensor, sensor->odr,
+			err = st_lsm6dsx_check_odr(sensor, sensor->hwfifo_odr_mHz,
 						   &data);
 			if (err < 0)
 				return err;
@@ -713,7 +714,7 @@ st_lsm6dsx_update_samples_to_discard(struct st_lsm6dsx_sensor *sensor)
 
 	data = &hw->settings->samples_to_discard[sensor->id];
 	for (i = 0; i < ST_LSM6DSX_ODR_LIST_SIZE; i++) {
-		if (data->val[i].milli_hz == sensor->odr) {
+		if (data->val[i].milli_hz == sensor->hwfifo_odr_mHz) {
 			sensor->samples_to_discard = data->val[i].samples;
 			return;
 		}
@@ -799,6 +800,59 @@ static const struct iio_buffer_setup_ops st_lsm6dsx_buffer_ops = {
 	.postdisable = st_lsm6dsx_buffer_postdisable,
 };
 
+static ssize_t st_lsm6dsx_hwfifo_odr_show(struct device *dev,
+					  struct device_attribute *attr, char *buf)
+{
+	struct st_lsm6dsx_sensor *sensor = iio_priv(dev_to_iio_dev(dev));
+
+	return sysfs_emit(buf, "%d.%03d\n", sensor->hwfifo_odr_mHz / 1000,
+			  sensor->hwfifo_odr_mHz % 1000);
+}
+
+static ssize_t st_lsm6dsx_hwfifo_odr_store(struct device *dev,
+					   struct device_attribute *attr,
+					   const char *buf, size_t len)
+{
+	struct iio_dev *iio_dev = dev_to_iio_dev(dev);
+	struct st_lsm6dsx_sensor *sensor = iio_priv(iio_dev);
+	int integer, milli;
+	int ret;
+	u32 hwfifo_odr;
+	u8 data;
+
+	if (!iio_device_claim_direct(iio_dev))
+		return -EBUSY;
+
+	ret = iio_str_to_fixpoint(buf, 100, &integer, &milli);
+	if (ret)
+		goto out;
+
+	hwfifo_odr = integer * 1000 + milli;
+	ret = st_lsm6dsx_check_odr(sensor, hwfifo_odr, &data);
+	if (ret < 0)
+		goto out;
+
+	hwfifo_odr = ret;
+
+	/* the batch data rate must not exceed the sensor output data rate */
+	if (hwfifo_odr <= sensor->odr)
+		sensor->hwfifo_odr_mHz = hwfifo_odr;
+	else
+		ret = -EINVAL;
+
+out:
+	iio_device_release_direct(iio_dev);
+
+	return ret < 0 ? ret : len;
+}
+
+static IIO_DEV_ATTR_SAMP_FREQ(0664, st_lsm6dsx_hwfifo_odr_show, st_lsm6dsx_hwfifo_odr_store);
+
+static const struct iio_dev_attr *st_lsm6dsx_buffer_attrs[] = {
+	&iio_dev_attr_sampling_frequency,
+	NULL
+};
+
 int st_lsm6dsx_fifo_setup(struct st_lsm6dsx_hw *hw)
 {
 	int i, ret;
@@ -807,8 +861,9 @@ int st_lsm6dsx_fifo_setup(struct st_lsm6dsx_hw *hw)
 		if (!hw->iio_devs[i])
 			continue;
 
-		ret = devm_iio_kfifo_buffer_setup(hw->dev, hw->iio_devs[i],
-						  &st_lsm6dsx_buffer_ops);
+		ret = devm_iio_kfifo_buffer_setup_ext(hw->dev, hw->iio_devs[i],
+						      &st_lsm6dsx_buffer_ops,
+						      st_lsm6dsx_buffer_attrs);
 		if (ret)
 			return ret;
 	}
diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
index c65ad49829e7..216160549b5a 100644
--- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
+++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
@@ -1847,10 +1847,12 @@ static int st_lsm6dsx_write_raw(struct iio_dev *iio_dev,
 
 		val = val * 1000 + val2 / 1000;
 		val = st_lsm6dsx_check_odr(sensor, val, &data);
-		if (val < 0)
+		if (val < 0) {
 			err = val;
-		else
+		} else {
 			sensor->odr = val;
+			sensor->hwfifo_odr_mHz = val;
+		}
 		break;
 	}
 	default:
@@ -2384,6 +2386,7 @@ static struct iio_dev *st_lsm6dsx_alloc_iiodev(struct st_lsm6dsx_hw *hw,
 	sensor->id = id;
 	sensor->hw = hw;
 	sensor->odr = hw->settings->odr_table[id].odr_avl[0].milli_hz;
+	sensor->hwfifo_odr_mHz = sensor->odr;
 	sensor->gain = hw->settings->fs_table[id].fs_avl[0].gain;
 	sensor->watermark = 1;
 
diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_shub.c b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_shub.c
index 3c5e65dc0f97..d6a1eeb151ca 100644
--- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_shub.c
+++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_shub.c
@@ -640,6 +640,7 @@ __st_lsm6dsx_shub_write_raw(struct iio_dev *iio_dev,
 
 		sensor->ext_info.slv_odr = val;
 		sensor->odr = odr;
+		sensor->hwfifo_odr_mHz = odr;
 		return 0;
 	}
 	case IIO_CHAN_INFO_SCALE:
@@ -746,6 +747,7 @@ st_lsm6dsx_shub_alloc_iiodev(struct st_lsm6dsx_hw *hw,
 	sensor->id = id;
 	sensor->hw = hw;
 	sensor->odr = hw->settings->odr_table[ref_id].odr_avl[0].milli_hz;
+	sensor->hwfifo_odr_mHz = sensor->odr;
 	sensor->ext_info.slv_odr = info->odr_table.odr_avl[0].milli_hz;
 	sensor->gain = info->fs_table.fs_avl[0].gain;
 	sensor->ext_info.settings = info;
-- 
2.39.5

Re: [PATCH v3 0/2] iio: imu: st_lsm6dsx: Decouple sensor ODR from FIFO batch data rate

[Jonathan Cameron]

On Fri, 17 Oct 2025 18:42:53 +0200
Francesco Lavra <flavra@baylibre.com> wrote:

> The rate at which accelerometer or gyroscope sensor samples are fed
> to the hardware FIFO (batch data rate, or BDR) does not have to
> coincide with the sensor sampling frequency (output data rate, or
> ODR); the only requirement is for the BDR to not be greater than
> the ODR. Having a BDR lower than the ODR is useful in cases where
> an application requires a high sampling rate for accurate detection
> of motion events (e.g. wakeup events), but wants to read sensor
> sample values from the device buffer at a lower data rate (e.g. to
> minimize the amount of I2C or SPI traffic and the rate of periodic
> interrupts).
> This change set amends the st_lsm6dsx IIO driver to support the above
> use case. The first commit is a trivial fix to the source code comment
> that indicates what measurement unit is used for the `odr` field of
> struct st_lsm6ds_sensor, while the second commit introduces a new
> `hwfifo_odr_mHz` field in the same struct to implement the new functionality.
> 
Applied to the togreg branch of iio.git which is initially pushed out as testing
for the autobuilders to poke at it.

Thanks

Jonathan