[PATCH v3 0/2] iio: pressure: add Sensirion SDP31 driver

[PATCH v3 0/2] iio: pressure: add Sensirion SDP31 driver

[Muhammad Abu Bakar]

This series adds support for the Sensirion SDP31 differential pressure
sensor, an I2C device that also reports temperature.

The SDP31 uses a completely different I2C command protocol from the
already supported SDP500 (command-triggered measurements with a per-word
CRC-8), so extending the sdp500 driver does not make sense. No compatible
parts from other vendors were found.

Patch 1 adds the device tree binding.
Patch 2 adds the IIO driver, which exposes differential pressure and
temperature channels and validates each measurement using the sensor's
CRC-8 checksum.

The driver was developed and tested on an SDP31 wired to the I2C bus of
a Raspberry Pi 4.

Changes since v2:
- Remove leftover development annotation comments from the driver.
- Drop the SDP31_TEMP_SCALE define and use the value inline.
- In sdp31_send_cmd(), separate the declaration of ret from the call so
  the call sits next to its error check.
- Add blank lines before the trailing return statements.
- Wait for the sensor's power-up time (datasheet t_PU) after enabling the
  regulator, before the first I2C transaction.

Changes since v1:
- dt-bindings: make vdd-supply required, and enable the regulator in the
  driver using devm_regulator_get_enable().
- Move the MAINTAINERS entry into the dt-bindings patch; the driver patch
  only adds its own file.
- Populate the CRC-8 table with DO_ONCE() to avoid a race between
  concurrent probes.
- Use devm_mutex_init() and take the lock inside sdp31_measure() using
  guard(mutex).
- Build the command with __be16/cpu_to_be16() and parse the reply with
  get_unaligned_be16().
- Use a named initializer in the i2c_device_id table.

v1: https://lore.kernel.org/linux-iio/20260919223650.13396-1-m.abubakar365@yahoo.com/
v2: https://lore.kernel.org/linux-iio/20260920164533.31988-1-m.abubakar365@yahoo.com/

Muhammad Abu Bakar (2):
  dt-bindings: iio: pressure: add Sensirion SDP31
  iio: pressure: add Sensirion SDP31 driver

 .../iio/pressure/sensirion,sdp31.yaml         |  41 ++++
 MAINTAINERS                                   |   6 +
 drivers/iio/pressure/Kconfig                  |  11 +
 drivers/iio/pressure/Makefile                 |   1 +
 drivers/iio/pressure/sdp31.c                  | 213 ++++++++++++++++++
 5 files changed, 272 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/pressure/sensirion,sdp31.yaml
 create mode 100644 drivers/iio/pressure/sdp31.c

-- 
2.43.0

[PATCH v3 1/2] dt-bindings: iio: pressure: add Sensirion SDP31

[Muhammad Abu Bakar]

Add device tree bindings for the Sensirion SDP31 differential pressure
sensor, an I2C device that also reports temperature.

Signed-off-by: Muhammad Abu Bakar <m.abubakar365@yahoo.com>
---
 .../iio/pressure/sensirion,sdp31.yaml         | 41 +++++++++++++++++++
 MAINTAINERS                                   |  5 +++
 2 files changed, 46 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/pressure/sensirion,sdp31.yaml

diff --git a/Documentation/devicetree/bindings/iio/pressure/sensirion,sdp31.yaml b/Documentation/devicetree/bindings/iio/pressure/sensirion,sdp31.yaml
new file mode 100644
index 000000000..a98e7c97e
--- /dev/null
+++ b/Documentation/devicetree/bindings/iio/pressure/sensirion,sdp31.yaml
@@ -0,0 +1,41 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/pressure/sensirion,sdp31.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Sensirion SDP31 differential pressure sensor
+
+maintainers:
+  - Muhammad Abu Bakar <m.abubakar365@yahoo.com>
+
+description: |
+  Differential pressure sensor from Sensirion with an I2C interface.
+
+properties:
+  compatible:
+    const: sensirion,sdp31
+
+  reg:
+    maxItems: 1
+
+  vdd-supply: true
+
+required:
+  - compatible
+  - reg
+  - vdd-supply
+
+additionalProperties: false
+
+examples:
+  - |
+    i2c {
+      #address-cells = <1>;
+      #size-cells = <0>;
+      pressure@21 {
+        compatible = "sensirion,sdp31";
+        reg = <0x21>;
+        vdd-supply = <&vdd_3v3>;
+      };
+    };
diff --git a/MAINTAINERS b/MAINTAINERS
index 214aeee76..e285147be 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -24855,6 +24855,11 @@ S:	Maintained
 F:	Documentation/devicetree/bindings/iio/chemical/sensirion,scd4x.yaml
 F:	drivers/iio/chemical/scd4x.c
 
+SENSIRION SDP31 DIFFERENTIAL PRESSURE SENSOR DRIVER
+M:	Muhammad Abu Bakar <m.abubakar365@yahoo.com>
+S:	Maintained
+F:	Documentation/devicetree/bindings/iio/pressure/sensirion,sdp31.yaml
+
 SENSIRION SDP500 DIFFERENTIAL PRESSURE SENSOR DRIVER
 M:	Petar Stoykov <petar.stoykov@prodrive-technologies.com>
 S:	Maintained
-- 
2.43.0

[PATCH v3 2/2] iio: pressure: add Sensirion SDP31 driver

[Muhammad Abu Bakar]

Add an IIO driver for the Sensirion SDP31 differential pressure sensor.
The device is accessed over I2C and reports differential pressure and
temperature. Each measurement is validated using the sensor's CRC-8
checksum.

Tested on an SDP31 connected to a Raspberry Pi 4 I2C bus.

Signed-off-by: Muhammad Abu Bakar <m.abubakar365@yahoo.com>
---
 MAINTAINERS                   |   1 +
 drivers/iio/pressure/Kconfig  |  11 ++
 drivers/iio/pressure/Makefile |   1 +
 drivers/iio/pressure/sdp31.c  | 213 ++++++++++++++++++++++++++++++++++
 4 files changed, 226 insertions(+)
 create mode 100644 drivers/iio/pressure/sdp31.c

diff --git a/MAINTAINERS b/MAINTAINERS
index e285147be..a053a530e 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -24859,6 +24859,7 @@ SENSIRION SDP31 DIFFERENTIAL PRESSURE SENSOR DRIVER
 M:	Muhammad Abu Bakar <m.abubakar365@yahoo.com>
 S:	Maintained
 F:	Documentation/devicetree/bindings/iio/pressure/sensirion,sdp31.yaml
+F:	drivers/iio/pressure/sdp31.c
 
 SENSIRION SDP500 DIFFERENTIAL PRESSURE SENSOR DRIVER
 M:	Petar Stoykov <petar.stoykov@prodrive-technologies.com>
diff --git a/drivers/iio/pressure/Kconfig b/drivers/iio/pressure/Kconfig
index 838a8340c..58172639c 100644
--- a/drivers/iio/pressure/Kconfig
+++ b/drivers/iio/pressure/Kconfig
@@ -286,6 +286,17 @@ config MS5637
 	  This driver can also be built as a module. If so, the module will
 	  be called ms5637.
 
+config SDP31
+	tristate "Sensirion SDP31 differential pressure sensor I2C driver"
+	depends on I2C
+	select CRC8
+	help
+	  Say Y here to build support for Sensirion SDP31 differential pressure
+	  sensor I2C driver.
+
+	  To compile this driver as a module, choose M here: the core module
+	  will be called sdp31.
+
 config SDP500
 	tristate "Sensirion SDP500 differential pressure sensor I2C driver"
 	depends on I2C
diff --git a/drivers/iio/pressure/Makefile b/drivers/iio/pressure/Makefile
index bc0d11a20..5279a0ebd 100644
--- a/drivers/iio/pressure/Makefile
+++ b/drivers/iio/pressure/Makefile
@@ -35,6 +35,7 @@ obj-$(CONFIG_MS5611) += ms5611_core.o
 obj-$(CONFIG_MS5611_I2C) += ms5611_i2c.o
 obj-$(CONFIG_MS5611_SPI) += ms5611_spi.o
 obj-$(CONFIG_MS5637) += ms5637.o
+obj-$(CONFIG_SDP31) += sdp31.o
 obj-$(CONFIG_SDP500) += sdp500.o
 obj-$(CONFIG_IIO_ST_PRESS) += st_pressure.o
 st_pressure-y := st_pressure_core.o
diff --git a/drivers/iio/pressure/sdp31.c b/drivers/iio/pressure/sdp31.c
new file mode 100644
index 000000000..fd7cac027
--- /dev/null
+++ b/drivers/iio/pressure/sdp31.c
@@ -0,0 +1,213 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+#include <linux/cleanup.h>
+#include <linux/crc8.h>
+#include <linux/delay.h>
+#include <linux/i2c.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/once.h>
+#include <linux/regulator/consumer.h>
+#include <linux/unaligned.h>
+
+#include <linux/iio/iio.h>
+
+#define SDP31_CMD_TRIG_DP     0x362F
+#define SDP31_MEAS_DELAY_MS   50
+#define SDP31_POWERUP_TIME_MS 25   /* datasheet t_PU (max) */
+#define SDP31_CRC8_POLY       0x31
+#define SDP31_CRC8_INIT       0xff
+
+DECLARE_CRC8_TABLE(sdp31_crc8_table);
+
+struct sdp31_data {
+	struct i2c_client *client;
+	struct mutex lock; /* serializes access to the sensor */
+	u16 dp_scale;
+};
+
+struct sdp31_reading {
+	s16 pressure;
+	s16 temp;
+	u16 scale;
+};
+
+static int sdp31_send_cmd(struct i2c_client *client, u16 cmd)
+{
+	__be16 buf = cpu_to_be16(cmd);
+	int ret;
+
+	ret = i2c_master_send(client, (u8 *)&buf, sizeof(buf));
+	if (ret < 0)
+		return ret;
+
+	return (ret == sizeof(buf)) ? 0 : -EIO;
+}
+
+static int sdp31_check_crc(const u8 *word)
+{
+	if (crc8(sdp31_crc8_table, word, 2, SDP31_CRC8_INIT) != word[2])
+		return -EIO;
+
+	return 0;
+}
+
+static int sdp31_measure(struct sdp31_data *data, struct sdp31_reading *out)
+{
+	u8 rx[9];
+	int ret;
+
+	guard(mutex)(&data->lock);
+
+	ret = sdp31_send_cmd(data->client, SDP31_CMD_TRIG_DP);
+	if (ret)
+		return ret;
+
+	msleep(SDP31_MEAS_DELAY_MS);
+
+	ret = i2c_master_recv(data->client, rx, sizeof(rx));
+	if (ret < 0)
+		return ret;
+	if (ret != sizeof(rx))
+		return -EIO;
+
+	if (sdp31_check_crc(&rx[0]) ||
+	    sdp31_check_crc(&rx[3]) ||
+	    sdp31_check_crc(&rx[6]))
+		return -EIO;
+
+	out->pressure = (s16)get_unaligned_be16(&rx[0]);
+	out->temp = (s16)get_unaligned_be16(&rx[3]);
+	out->scale = get_unaligned_be16(&rx[6]);
+
+	return 0;
+}
+
+static int sdp31_read_raw(struct iio_dev *indio_dev,
+			  struct iio_chan_spec const *chan,
+			  int *val, int *val2, long mask)
+{
+	struct sdp31_data *data = iio_priv(indio_dev);
+	struct sdp31_reading r;
+	int ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		ret = sdp31_measure(data, &r);
+		if (ret)
+			return ret;
+		switch (chan->type) {
+		case IIO_PRESSURE:
+			*val = r.pressure;
+			return IIO_VAL_INT;
+		case IIO_TEMP:
+			*val = r.temp;
+			return IIO_VAL_INT;
+		default:
+			return -EINVAL;
+		}
+	case IIO_CHAN_INFO_SCALE:
+		switch (chan->type) {
+		case IIO_PRESSURE:
+			*val = 1;
+			*val2 = data->dp_scale * 1000;
+			return IIO_VAL_FRACTIONAL;
+		case IIO_TEMP:
+			/* raw / 200 = degC, so raw * 5 = milli-degC */
+			*val = 5;
+			return IIO_VAL_INT;
+		default:
+			return -EINVAL;
+		}
+	default:
+		return -EINVAL;
+	}
+}
+
+static const struct iio_info sdp31_info = {
+	.read_raw = sdp31_read_raw,
+};
+
+static const struct iio_chan_spec sdp31_channels[] = {
+	{
+		.type = IIO_PRESSURE,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+				      BIT(IIO_CHAN_INFO_SCALE),
+	},
+	{
+		.type = IIO_TEMP,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+				      BIT(IIO_CHAN_INFO_SCALE),
+	},
+};
+
+static int sdp31_probe(struct i2c_client *client)
+{
+	struct device *dev = &client->dev;
+	struct iio_dev *indio_dev;
+	struct sdp31_data *data;
+	struct sdp31_reading r;
+	int ret;
+
+	ret = devm_regulator_get_enable(dev, "vdd");
+	if (ret)
+		return dev_err_probe(dev, ret, "failed to enable regulator\n");
+
+	/* Wait for the sensor to be ready after power-up (datasheet t_PU). */
+	msleep(SDP31_POWERUP_TIME_MS);
+
+	indio_dev = devm_iio_device_alloc(dev, sizeof(*data));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	data = iio_priv(indio_dev);
+	data->client = client;
+
+	ret = devm_mutex_init(dev, &data->lock);
+	if (ret)
+		return ret;
+
+	/* The CRC table is shared by all instances; initialise it once. */
+	DO_ONCE(crc8_populate_msb, sdp31_crc8_table, SDP31_CRC8_POLY);
+
+	/* Confirm the sensor is present and learn its scale factor. */
+	ret = sdp31_measure(data, &r);
+	if (ret)
+		return dev_err_probe(dev, ret, "failed to read from sensor\n");
+	if (!r.scale)
+		return dev_err_probe(dev, -EINVAL, "invalid scale factor\n");
+	data->dp_scale = r.scale;
+
+	indio_dev->name = "sdp31";
+	indio_dev->info = &sdp31_info;
+	indio_dev->modes = INDIO_DIRECT_MODE;
+	indio_dev->channels = sdp31_channels;
+	indio_dev->num_channels = ARRAY_SIZE(sdp31_channels);
+
+	return devm_iio_device_register(dev, indio_dev);
+}
+
+static const struct i2c_device_id sdp31_id[] = {
+	{ .name = "sdp31" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, sdp31_id);
+
+static const struct of_device_id sdp31_of_match[] = {
+	{ .compatible = "sensirion,sdp31" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, sdp31_of_match);
+
+static struct i2c_driver sdp31_driver = {
+	.driver = {
+		.name = "sdp31",
+		.of_match_table = sdp31_of_match,
+	},
+	.probe = sdp31_probe,
+	.id_table = sdp31_id,
+};
+module_i2c_driver(sdp31_driver);
+
+MODULE_AUTHOR("Muhammad Abu Bakar");
+MODULE_DESCRIPTION("Sensirion SDP31 differential pressure sensor");
+MODULE_LICENSE("GPL");
-- 
2.43.0

Re: [PATCH v3 1/2] dt-bindings: iio: pressure: add Sensirion SDP31

[Jonathan Cameron]

On Sat, 26 Sep 2026 20:41:17 +0500
Muhammad Abu Bakar <m.abubakar365@yahoo.com> wrote:

> Add device tree bindings for the Sensirion SDP31 differential pressure
> sensor, an I2C device that also reports temperature.
> 
> Signed-off-by: Muhammad Abu Bakar <m.abubakar365@yahoo.com>
I think you have been missing some replies for some reason.

See https://lore.kernel.org/all/20260920014032.2cc3c851@jic23-hlaptop/
Also the reply Krzysztof sent to point out you hadn't addressed all
the feedback on v1.

If you disagree with any suggestions then reply to that email.

Reviewers tend to stop reviewing very quickly if they see that stuff
they raised in previous versions hasn't been addressed yet.

Jonathan


> ---
>  .../iio/pressure/sensirion,sdp31.yaml         | 41 +++++++++++++++++++
>  MAINTAINERS                                   |  5 +++
>  2 files changed, 46 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/iio/pressure/sensirion,sdp31.yaml
> 
> diff --git a/Documentation/devicetree/bindings/iio/pressure/sensirion,sdp31.yaml b/Documentation/devicetree/bindings/iio/pressure/sensirion,sdp31.yaml
> new file mode 100644
> index 000000000..a98e7c97e
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/pressure/sensirion,sdp31.yaml
> @@ -0,0 +1,41 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/iio/pressure/sensirion,sdp31.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Sensirion SDP31 differential pressure sensor
> +
> +maintainers:
> +  - Muhammad Abu Bakar <m.abubakar365@yahoo.com>
> +
> +description: |
> +  Differential pressure sensor from Sensirion with an I2C interface.
> +
> +properties:
> +  compatible:
> +    const: sensirion,sdp31
> +
> +  reg:
> +    maxItems: 1
> +
> +  vdd-supply: true
> +
> +required:
> +  - compatible
> +  - reg
> +  - vdd-supply
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    i2c {
> +      #address-cells = <1>;
> +      #size-cells = <0>;
> +      pressure@21 {
> +        compatible = "sensirion,sdp31";
> +        reg = <0x21>;
> +        vdd-supply = <&vdd_3v3>;
> +      };
> +    };
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 214aeee76..e285147be 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -24855,6 +24855,11 @@ S:	Maintained
>  F:	Documentation/devicetree/bindings/iio/chemical/sensirion,scd4x.yaml
>  F:	drivers/iio/chemical/scd4x.c
>  
> +SENSIRION SDP31 DIFFERENTIAL PRESSURE SENSOR DRIVER
> +M:	Muhammad Abu Bakar <m.abubakar365@yahoo.com>
> +S:	Maintained
> +F:	Documentation/devicetree/bindings/iio/pressure/sensirion,sdp31.yaml
> +
>  SENSIRION SDP500 DIFFERENTIAL PRESSURE SENSOR DRIVER
>  M:	Petar Stoykov <petar.stoykov@prodrive-technologies.com>
>  S:	Maintained

Re: [PATCH v3 2/2] iio: pressure: add Sensirion SDP31 driver

[Jonathan Cameron]

On Sat, 26 Sep 2026 20:41:18 +0500
Muhammad Abu Bakar <m.abubakar365@yahoo.com> wrote:

> Add an IIO driver for the Sensirion SDP31 differential pressure sensor.
> The device is accessed over I2C and reports differential pressure and
> temperature. Each measurement is validated using the sensor's CRC-8
> checksum.
> 
> Tested on an SDP31 connected to a Raspberry Pi 4 I2C bus.
> 
> Signed-off-by: Muhammad Abu Bakar <m.abubakar365@yahoo.com>
Hi. 

Given you are going to probably need to changes stuff in the dt binding
and so do a v4, various comments inline.  Mostly optimization suggestions.

Jonathan

>  st_pressure-y := st_pressure_core.o
> diff --git a/drivers/iio/pressure/sdp31.c b/drivers/iio/pressure/sdp31.c
> new file mode 100644
> index 000000000..fd7cac027
> --- /dev/null
> +++ b/drivers/iio/pressure/sdp31.c

> +static int sdp31_measure(struct sdp31_data *data, struct sdp31_reading *out)
> +{
> +	u8 rx[9];
> +	int ret;
> +
> +	guard(mutex)(&data->lock);
> +
> +	ret = sdp31_send_cmd(data->client, SDP31_CMD_TRIG_DP);
> +	if (ret)
> +		return ret;
> +
> +	msleep(SDP31_MEAS_DELAY_MS);
> +
> +	ret = i2c_master_recv(data->client, rx, sizeof(rx));

Given there is only a one time read of scale and that i2c is a rather
slow bus, can we do a short read when we only want the temperature
and pressure?  The datasheet mentions Nack + stop is
sufficient to stop the read out sequence and that is IIRC the
normal end of an i2c read sequence. So it 'should' be fine to just
read fewer bytes.

> +	if (ret < 0)
> +		return ret;
> +	if (ret != sizeof(rx))
> +		return -EIO;
> +
> +	if (sdp31_check_crc(&rx[0]) ||
> +	    sdp31_check_crc(&rx[3]) ||
> +	    sdp31_check_crc(&rx[6]))
> +		return -EIO;
> +
> +	out->pressure = (s16)get_unaligned_be16(&rx[0]);
> +	out->temp = (s16)get_unaligned_be16(&rx[3]);
> +	out->scale = get_unaligned_be16(&rx[6]);
> +
> +	return 0;
> +}

> +
> +static int sdp31_probe(struct i2c_client *client)
> +{
> +	struct device *dev = &client->dev;
> +	struct iio_dev *indio_dev;
> +	struct sdp31_data *data;
> +	struct sdp31_reading r;
> +	int ret;
> +
> +	ret = devm_regulator_get_enable(dev, "vdd");
> +	if (ret)
> +		return dev_err_probe(dev, ret, "failed to enable regulator\n");
> +
> +	/* Wait for the sensor to be ready after power-up (datasheet t_PU). */
> +	msleep(SDP31_POWERUP_TIME_MS);
> +
> +	indio_dev = devm_iio_device_alloc(dev, sizeof(*data));
> +	if (!indio_dev)
> +		return -ENOMEM;
> +
> +	data = iio_priv(indio_dev);
> +	data->client = client;
> +
> +	ret = devm_mutex_init(dev, &data->lock);
> +	if (ret)
> +		return ret;
> +
> +	/* The CRC table is shared by all instances; initialise it once. */

I would argue that is obvious, so no comment needed.

> +	DO_ONCE(crc8_populate_msb, sdp31_crc8_table, SDP31_CRC8_POLY);
> +
> +	/* Confirm the sensor is present and learn its scale factor. */

If you end up with with a specific call to get the scale factor this
comment will become excessive (see below).

> +	ret = sdp31_measure(data, &r);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "failed to read from sensor\n");
> +	if (!r.scale)
> +		return dev_err_probe(dev, -EINVAL, "invalid scale factor\n");

See above. This is the only time we actually read the scale - so perhaps
we can save some traffic on every other access. Most likely that would give
you a different command for this scale read back.

> +	data->dp_scale = r.scale;
> +
> +	indio_dev->name = "sdp31";
> +	indio_dev->info = &sdp31_info;
> +	indio_dev->modes = INDIO_DIRECT_MODE;
> +	indio_dev->channels = sdp31_channels;
> +	indio_dev->num_channels = ARRAY_SIZE(sdp31_channels);
> +
> +	return devm_iio_device_register(dev, indio_dev);
> +}