[PATCH v4 0/2] Add support for Analog Devices MAX30210

[PATCH v4 0/2] Add support for Analog Devices MAX30210

[John Erasmus Mari Geronimo]

This series adds support for the Analog Devices MAX30210 I2C
temperature sensor.

The device provides a 16-bit temperature output and includes
features such as a hardware FIFO, programmable sampling rate,
threshold alarms, and interrupt support. These capabilities map
naturally to the IIO subsystem, particularly the buffered interface
and event framework -- hwmon has no equivalent buffered-capture
framework, and its alarm attributes are polled rather than
interrupt-driven, so there is no path to supporting the FIFO or the
autonomous threshold comparators there.

Although the MAX30210 belongs to the same device family as the
MAX30208, it is implemented as a separate driver. The MAX30210 has
a significantly different feature set, including a 64-sample hardware
FIFO with configurable watermark interrupts, programmable sampling
rates, and event support. These features require buffered operation
and IRQ-driven data handling which are not present in the MAX30208
driver (which talks to the device directly via i2c_smbus_*() calls
with no regmap, and has no IIO buffer or event interface at all).

In addition, the MAX30210 uses a different register map and a more
flexible I2C address selection scheme. Supporting both devices in a
single driver would introduce substantial conditional logic, so a
separate driver keeps the implementation simpler and easier to
maintain.

Patch 1 adds the devicetree binding.
Patch 2 adds the IIO driver implementation.

Changes since v3:
https://lore.kernel.org/all/cover.1789032019.git.johnerasmusmari.geronimo@analog.com/
- regmap_noinc_read() for FIFO reads instead of regmap_bulk_read(),
  which (combined with regmap caching) could silently return stale
  cached values of unrelated registers instead of real FIFO data.
- Mark both bytes of TEMP_DATA_REG volatile for the same reason.
- Decouple threshold events from the buffer via a refcounted
  autoconv_get()/autoconv_put() pair, so either can be used
  independently or concurrently.
- Don't let a single-shot direct-mode read race with/clobber
  autonomous conversion mode if a threshold event or the buffer is
  already using it -- return -EBUSY instead.
- Don't hard-fail probe when there is no interrupt; fall back to
  direct-mode-only operation.
- Fix devm teardown ordering so an in-flight interrupt can't use a
  freed event interface on removal.
- Re-assert the powerdown GPIO on removal so the device reaches
  standby instead of staying powered indefinitely.
- Style/API fixes from review (register/field grouping, _MASK
  naming, FIELD_PREP/regmap_assign_bits usage, C99 initializers,
  dropped redundant i2c_check_functionality() check, comment
  cleanup).

All of the above have been verified on real MAX30210 hardware
(Raspberry Pi 4 test rig), including the no-IRQ fallback, buffer and
event refcounting (independently and concurrently), rmmod/insmod
under live interrupts, powerdown GPIO assertion on removal, and FIFO
flush correctness.

Changes since v2:
https://lore.kernel.org/all/20260304122509.67931-1-johnerasmusmari.geronimo@analog.com/
- Fix FIFO byte-count handling and sample decoding.
- Fix IIO debug register read/write access.
- Validate event threshold values and sampling-frequency register values.
- Return the correct sampling-frequency format and reject direct reads
  while buffered capture is enabled.
- Clean up the Kconfig entry and device-tree supply declaration.

John Erasmus Mari Geronimo (2):
  dt-bindings: iio: temperature: add ADI MAX30210
  iio: temperature: add support for Analog Devices MAX30210

 .../iio/temperature/adi,max30210.yaml         |  61 ++
 MAINTAINERS                                   |   8 +
 drivers/iio/temperature/Kconfig               |  13 +
 drivers/iio/temperature/Makefile              |   1 +
 drivers/iio/temperature/max30210.c            | 788 ++++++++++++++++++
 5 files changed, 871 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/temperature/adi,max30210.yaml
 create mode 100644 drivers/iio/temperature/max30210.c

-- 
2.34.1

[PATCH v4 1/2] dt-bindings: iio: temperature: add ADI MAX30210

[John Erasmus Mari Geronimo]

Add device tree binding documentation for the Analog Devices
MAX30210 temperature sensor.

Signed-off-by: John Erasmus Mari Geronimo <johnerasmusmari.geronimo@analog.com>
---
 .../iio/temperature/adi,max30210.yaml         | 61 +++++++++++++++++++
 MAINTAINERS                                   |  7 +++
 2 files changed, 68 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/temperature/adi,max30210.yaml

diff --git a/Documentation/devicetree/bindings/iio/temperature/adi,max30210.yaml b/Documentation/devicetree/bindings/iio/temperature/adi,max30210.yaml
new file mode 100644
index 0000000000000..8bfd154bbc438
--- /dev/null
+++ b/Documentation/devicetree/bindings/iio/temperature/adi,max30210.yaml
@@ -0,0 +1,61 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+# Copyright 2026 Analog Devices Inc.
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/temperature/adi,max30210.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Analog Devices MAX30210 Temperature Sensor
+
+maintainers:
+  - John Erasmus Mari Geronimo <johnerasmusmari.geronimo@analog.com>
+
+description: |
+  The MAX30210 is a temperature sensor with an I2C interface.
+  https://www.analog.com/media/en/technical-documentation/data-sheets/max30210.pdf
+
+properties:
+  compatible:
+    enum:
+      - adi,max30210
+
+  reg:
+    maxItems: 1
+
+  vdd-supply: true
+
+  powerdown-gpios:
+    description: GPIO connected to the CVT/PDB pin (active low).
+    maxItems: 1
+
+  interrupts:
+    description: Connected to INT pin. Interrupt triggered on both rising and falling edges.
+    maxItems: 1
+
+required:
+  - compatible
+  - reg
+  - vdd-supply
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/irq.h>
+    #include <dt-bindings/gpio/gpio.h>
+
+    i2c {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        temperature-sensor@40 {
+            compatible = "adi,max30210";
+            reg = <0x40>;
+            vdd-supply = <&vdd>;
+            powerdown-gpios = <&gpio 12 GPIO_ACTIVE_LOW>;
+
+            interrupt-parent = <&gpio>;
+            interrupts = <17 IRQ_TYPE_EDGE_BOTH>;
+        };
+    };
+...
diff --git a/MAINTAINERS b/MAINTAINERS
index 396d4e76dccc2..6eb3cf66f431c 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1653,6 +1653,13 @@ W:	https://ez.analog.com/linux-software-drivers
 F:	Documentation/devicetree/bindings/iio/dac/adi,max22007.yaml
 F:	drivers/iio/dac/max22007.c
 
+ANALOG DEVICES INC MAX30210 DRIVER
+M:	John Erasmus Mari Geronimo <johnerasmusmari.geronimo@analog.com>
+L:	linux-iio@vger.kernel.org
+S:	Supported
+W:	https://ez.analog.com/linux-software-drivers
+F:	Documentation/devicetree/bindings/iio/temperature/adi,max30210.yaml
+
 ANALOG DEVICES INC ADA4250 DRIVER
 M:	Antoniu Miclaus <antoniu.miclaus@analog.com>
 L:	linux-iio@vger.kernel.org
-- 
2.34.1

[PATCH v4 2/2] iio: temperature: add support for Analog Devices MAX30210

[John Erasmus Mari Geronimo]

Add support for the Analog Devices MAX30210 I2C temperature
sensor.

The driver uses regmap for register access and integrates with
the IIO framework. It supports:

- Direct mode temperature conversion
- Configurable sampling frequency
- Threshold events
- FIFO operation with IIO kfifo buffer support
- Optional interrupt-driven data ready signaling

The device provides 16-bit signed temperature data and a
64-sample FIFO.

Signed-off-by: John Erasmus Mari Geronimo <johnerasmusmari.geronimo@analog.com>
---
 MAINTAINERS                        |   1 +
 drivers/iio/temperature/Kconfig    |  13 +
 drivers/iio/temperature/Makefile   |   1 +
 drivers/iio/temperature/max30210.c | 788 +++++++++++++++++++++++++++++
 4 files changed, 803 insertions(+)
 create mode 100644 drivers/iio/temperature/max30210.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 6eb3cf66f431c..e479c64a284e0 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1659,6 +1659,7 @@ L:	linux-iio@vger.kernel.org
 S:	Supported
 W:	https://ez.analog.com/linux-software-drivers
 F:	Documentation/devicetree/bindings/iio/temperature/adi,max30210.yaml
+F:	drivers/iio/temperature/max30210.c
 
 ANALOG DEVICES INC ADA4250 DRIVER
 M:	Antoniu Miclaus <antoniu.miclaus@analog.com>
diff --git a/drivers/iio/temperature/Kconfig b/drivers/iio/temperature/Kconfig
index 9328b2250aced..05b3af6872b31 100644
--- a/drivers/iio/temperature/Kconfig
+++ b/drivers/iio/temperature/Kconfig
@@ -152,6 +152,19 @@ config MAX30208
 	  This driver can also be built as a module. If so, the module
 	  will be called max30208.
 
+config MAX30210
+	tristate "Analog Devices MAX30210 temperature sensor"
+	depends on I2C
+	select REGMAP_I2C
+	select IIO_BUFFER
+	select IIO_KFIFO_BUF
+	help
+	  If you say yes here you get support for MAX30210 low-power digital
+	  temperature sensor chip connected via I2C.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called max30210.
+
 config MAX31856
 	tristate "MAX31856 thermocouple sensor"
 	depends on SPI
diff --git a/drivers/iio/temperature/Makefile b/drivers/iio/temperature/Makefile
index 07d6e65709f7f..e5aad14dc09b9 100644
--- a/drivers/iio/temperature/Makefile
+++ b/drivers/iio/temperature/Makefile
@@ -8,6 +8,7 @@ obj-$(CONFIG_LTC2983) += ltc2983.o
 obj-$(CONFIG_HID_SENSOR_TEMP) += hid-sensor-temperature.o
 obj-$(CONFIG_MAXIM_THERMOCOUPLE) += maxim_thermocouple.o
 obj-$(CONFIG_MAX30208) += max30208.o
+obj-$(CONFIG_MAX30210) += max30210.o
 obj-$(CONFIG_MAX31856) += max31856.o
 obj-$(CONFIG_MAX31865) += max31865.o
 obj-$(CONFIG_MCP9600) += mcp9600.o
diff --git a/drivers/iio/temperature/max30210.c b/drivers/iio/temperature/max30210.c
new file mode 100644
index 0000000000000..04123d51c6da4
--- /dev/null
+++ b/drivers/iio/temperature/max30210.c
@@ -0,0 +1,788 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Analog Devices MAX30210 I2C Temperature Sensor driver
+ *
+ * Copyright 2026 Analog Devices Inc.
+ */
+
+#include <linux/array_size.h>
+#include <linux/bitfield.h>
+#include <linux/bitops.h>
+#include <linux/delay.h>
+#include <linux/gpio/consumer.h>
+#include <linux/i2c.h>
+#include <linux/iio/buffer.h>
+#include <linux/iio/events.h>
+#include <linux/iio/iio.h>
+#include <linux/iio/kfifo_buf.h>
+#include <linux/iio/sysfs.h>
+#include <linux/mutex.h>
+#include <linux/regmap.h>
+#include <linux/regulator/consumer.h>
+#include <linux/time.h>
+#include <linux/types.h>
+#include <linux/unaligned.h>
+#include <linux/units.h>
+
+#define MAX30210_STATUS_REG			0x00
+#define   MAX30210_STATUS_A_FULL_MASK		BIT(7)
+#define   MAX30210_STATUS_TEMP_RDY_MASK	BIT(6)
+#define   MAX30210_STATUS_TEMP_DEC_MASK	BIT(5)
+#define   MAX30210_STATUS_TEMP_INC_MASK	BIT(4)
+#define   MAX30210_STATUS_TEMP_LO_MASK		BIT(3)
+#define   MAX30210_STATUS_TEMP_HI_MASK		BIT(2)
+#define   MAX30210_STATUS_PWR_RDY		BIT(0)
+#define MAX30210_INT_EN_REG			0x02
+#define MAX30210_FIFO_DATA_REG			0x08
+#define MAX30210_FIFO_CONF_1_REG		0x09
+#define   MAX30210_FIFOCONF1_A_FULL_MASK	GENMASK(5, 0)
+#define MAX30210_FIFO_CONF_2_REG		0x0A
+#define   MAX30210_FIFOCONF2_FLUSH_FIFO		BIT(4)
+#define MAX30210_SYS_CONF_REG			0x11
+#define   MAX30210_SYSCONF_RESET		BIT(0)
+#define MAX30210_PIN_CONF_REG			0x12
+#define   MAX30210_PINCONF_EXT_CNV_EN		BIT(7)
+#define   MAX30210_PINCONF_EXT_CVT_ICFG		BIT(6)
+#define   MAX30210_PINCONF_INT_FCFG_MASK	GENMASK(3, 2)
+#define   MAX30210_PINCONF_INT_OCFG_MASK	GENMASK(1, 0)
+#define MAX30210_TEMP_ALM_HI_REG		0x22
+#define MAX30210_TEMP_ALM_LO_REG		0x24
+#define MAX30210_TEMP_INC_THRESH_REG		0x26
+#define MAX30210_TEMP_DEC_THRESH_REG		0x27
+#define MAX30210_TEMP_CONF_1_REG		0x28
+#define   MAX30210_TEMPCONF1_CHG_DET_EN		BIT(3)
+#define   MAX30210_TEMPCONF1_RATE_CHG_FILTER_MASK	GENMASK(2, 0)
+#define MAX30210_TEMP_CONF_2_REG		0x29
+#define   MAX30210_TEMPCONF2_TEMP_PERIOD_MASK	GENMASK(3, 0)
+#define   MAX30210_TEMPCONF2_ALERT_MODE		BIT(7)
+#define MAX30210_TEMP_CONV_REG			0x2A
+#define   MAX30210_TEMPCONV_CONV_T		BIT(0)
+#define   MAX30210_TEMPCONV_AUTO		BIT(1)
+#define MAX30210_TEMP_DATA_REG			0x2B
+#define MAX30210_TEMP_SLOPE_REG			0x2D
+#define MAX30210_UNIQUE_ID_REG			0x30
+#define MAX30210_PART_ID_REG			0xFF
+
+#define MAX30210_PART_ID			0x45
+#define MAX30210_FIFO_SIZE			64
+#define MAX30210_FIFO_BYTES_PER_SAMPLE		3
+#define MAX30210_FIFO_TEMP_MASK			GENMASK(15, 0)
+#define MAX30210_FIFO_INVAL_DATA		GENMASK(23, 0)
+#define MAX30210_WATERMARK_DEFAULT		(0x40 - 0x1F)
+
+#define MAX30210_UNIQUE_ID_LEN			6
+#define MAX30210_EXT_CVT_FREQ_MIN		1
+#define MAX30210_EXT_CVT_FREQ_MAX		20
+
+struct max30210_state {
+	struct regmap *regmap;
+	/* Raw FIFO byte buffer */
+	u8 fifo_buf[MAX30210_FIFO_BYTES_PER_SAMPLE * MAX30210_FIFO_SIZE];
+	/* Protects autoconv_users and the autonomous-conversion enable bit */
+	struct mutex lock;
+	unsigned int autoconv_users;
+	u8 watermark;
+};
+
+static const int max30210_samp_freq_avail[][2] = {
+	{ 0, 15625 },
+	{ 0, 31250 },
+	{ 0, 62500 },
+	{ 0, 125000 },
+	{ 0, 250000 },
+	{ 0, 500000 },
+	{ 1, 0 },
+	{ 2, 0 },
+	{ 4, 0 },
+	{ 8, 0 },
+};
+
+static bool max30210_volatile_reg(struct device *dev, unsigned int reg)
+{
+	switch (reg) {
+	case MAX30210_STATUS_REG:
+	case MAX30210_FIFO_DATA_REG:
+	case MAX30210_FIFO_CONF_2_REG:
+	case MAX30210_TEMP_CONV_REG:
+	/*
+	 * TEMP_DATA_REG is a 16-bit value spanning two byte registers;
+	 * both must be volatile or regmap_bulk_read()'s range check falls
+	 * back to caching the second byte forever (see max30210_read_temp()).
+	 */
+	case MAX30210_TEMP_DATA_REG:
+	case MAX30210_TEMP_DATA_REG + 1:
+		return true;
+	default:
+		return false;
+	}
+}
+
+static const struct regmap_config max30210_regmap = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.max_register = MAX30210_PART_ID_REG,
+	.volatile_reg = max30210_volatile_reg,
+	.cache_type = REGCACHE_MAPLE,
+};
+
+static int max30210_read_temp(struct regmap *regmap, unsigned int reg,
+			      int *temp)
+{
+	__be16 val;
+	int ret;
+
+	ret = regmap_bulk_read(regmap, reg, &val, sizeof(val));
+	if (ret)
+		return ret;
+
+	*temp = sign_extend32(be16_to_cpu(val), 15);
+
+	return IIO_VAL_INT;
+}
+
+static int max30210_write_temp(struct regmap *regmap, unsigned int reg,
+			       int temp)
+{
+	__be16 val;
+
+	val = cpu_to_be16(temp);
+
+	return regmap_bulk_write(regmap, reg, &val, sizeof(val));
+}
+
+/* Keeps the device sampling autonomously while buffer and/or events need it. */
+static int max30210_autoconv_get(struct max30210_state *st)
+{
+	int ret = 0;
+
+	guard(mutex)(&st->lock);
+
+	if (st->autoconv_users == 0)
+		ret = regmap_write(st->regmap, MAX30210_TEMP_CONV_REG,
+				   MAX30210_TEMPCONV_AUTO | MAX30210_TEMPCONV_CONV_T);
+	if (!ret)
+		st->autoconv_users++;
+
+	return ret;
+}
+
+static int max30210_autoconv_put(struct max30210_state *st)
+{
+	int ret = 0;
+
+	guard(mutex)(&st->lock);
+
+	if (st->autoconv_users == 1)
+		ret = regmap_write(st->regmap, MAX30210_TEMP_CONV_REG, 0);
+	if (st->autoconv_users)
+		st->autoconv_users--;
+
+	return ret;
+}
+
+static void max30210_fifo_read(struct iio_dev *indio_dev)
+{
+	struct max30210_state *st = iio_priv(indio_dev);
+	int ret;
+
+	/*
+	 * FIFO_DATA_REG auto-increments in hardware; bulk_read would treat
+	 * each subsequent byte as a separate cacheable register.
+	 */
+	ret = regmap_noinc_read(st->regmap, MAX30210_FIFO_DATA_REG,
+				st->fifo_buf,
+				MAX30210_FIFO_BYTES_PER_SAMPLE * st->watermark);
+	if (ret) {
+		dev_err(&indio_dev->dev, "Failed to read from fifo.\n");
+		return;
+	}
+
+	for (unsigned int i = 0; i < st->watermark; i++) {
+		u32 raw = get_unaligned_be24(&st->fifo_buf[MAX30210_FIFO_BYTES_PER_SAMPLE * i]);
+		s16 temp;
+
+		if (raw == MAX30210_FIFO_INVAL_DATA) {
+			dev_err_ratelimited(&indio_dev->dev, "Invalid data\n");
+			continue;
+		}
+
+		temp = sign_extend32(FIELD_GET(MAX30210_FIFO_TEMP_MASK, raw), 15);
+
+		iio_push_to_buffers(indio_dev, &temp);
+	}
+}
+
+static irqreturn_t max30210_irq_handler(int irq, void *dev_id)
+{
+	struct iio_dev *indio_dev = dev_id;
+	struct max30210_state *st = iio_priv(indio_dev);
+	unsigned int status;
+	int ret;
+
+	ret = regmap_read(st->regmap, MAX30210_STATUS_REG, &status);
+	if (ret) {
+		dev_err(&indio_dev->dev, "Status read failed\n");
+		return IRQ_NONE;
+	}
+
+	if (status & MAX30210_STATUS_A_FULL_MASK)
+		max30210_fifo_read(indio_dev);
+
+	if (status & MAX30210_STATUS_TEMP_HI_MASK)
+		iio_push_event(indio_dev,
+			       IIO_UNMOD_EVENT_CODE(IIO_TEMP, 0,
+						    IIO_EV_TYPE_THRESH,
+						    IIO_EV_DIR_RISING),
+			       iio_get_time_ns(indio_dev));
+
+	if (status & MAX30210_STATUS_TEMP_LO_MASK)
+		iio_push_event(indio_dev,
+			       IIO_UNMOD_EVENT_CODE(IIO_TEMP, 0,
+						    IIO_EV_TYPE_THRESH,
+						    IIO_EV_DIR_FALLING),
+			       iio_get_time_ns(indio_dev));
+
+	return IRQ_HANDLED;
+}
+
+static int max30210_reg_access(struct iio_dev *indio_dev, unsigned int reg,
+			       unsigned int writeval, unsigned int *readval)
+{
+	struct max30210_state *st = iio_priv(indio_dev);
+
+	if (readval)
+		return regmap_read(st->regmap, reg, readval);
+
+	return regmap_write(st->regmap, reg, writeval);
+}
+
+static int max30210_read_event(struct iio_dev *indio_dev,
+			       const struct iio_chan_spec *chan,
+			       enum iio_event_type type,
+			       enum iio_event_direction dir,
+			       enum iio_event_info info, int *val, int *val2)
+{
+	struct max30210_state *st = iio_priv(indio_dev);
+
+	if (info != IIO_EV_INFO_VALUE)
+		return -EINVAL;
+
+	switch (dir) {
+	case IIO_EV_DIR_RISING:
+		switch (type) {
+		case IIO_EV_TYPE_THRESH:
+			return max30210_read_temp(st->regmap, MAX30210_TEMP_ALM_HI_REG, val);
+		default:
+			return -EINVAL;
+		}
+	case IIO_EV_DIR_FALLING:
+		switch (type) {
+		case IIO_EV_TYPE_THRESH:
+			return max30210_read_temp(st->regmap, MAX30210_TEMP_ALM_LO_REG, val);
+		default:
+			return -EINVAL;
+		}
+	default:
+		return -EINVAL;
+	}
+}
+
+static int max30210_write_event(struct iio_dev *indio_dev,
+				const struct iio_chan_spec *chan,
+				enum iio_event_type type,
+				enum iio_event_direction dir,
+				enum iio_event_info info, int val, int val2)
+{
+	struct max30210_state *st = iio_priv(indio_dev);
+
+	if (info != IIO_EV_INFO_VALUE)
+		return -EINVAL;
+
+	if (val < S16_MIN || val > S16_MAX)
+		return -EINVAL;
+
+	switch (dir) {
+	case IIO_EV_DIR_RISING:
+		switch (type) {
+		case IIO_EV_TYPE_THRESH:
+			return max30210_write_temp(st->regmap, MAX30210_TEMP_ALM_HI_REG, val);
+		default:
+			return -EINVAL;
+		}
+	case IIO_EV_DIR_FALLING:
+		switch (type) {
+		case IIO_EV_TYPE_THRESH:
+			return max30210_write_temp(st->regmap, MAX30210_TEMP_ALM_LO_REG, val);
+		default:
+			return -EINVAL;
+		}
+	default:
+		return -EINVAL;
+	}
+}
+
+static int max30210_read_event_config(struct iio_dev *indio_dev,
+				      const struct iio_chan_spec *chan,
+				      enum iio_event_type type,
+				      enum iio_event_direction dir)
+{
+	struct max30210_state *st = iio_priv(indio_dev);
+	unsigned int val;
+	int ret;
+
+	ret = regmap_read(st->regmap, MAX30210_INT_EN_REG, &val);
+	if (ret)
+		return ret;
+
+	switch (dir) {
+	case IIO_EV_DIR_RISING:
+		switch (type) {
+		case IIO_EV_TYPE_THRESH:
+			return FIELD_GET(MAX30210_STATUS_TEMP_HI_MASK, val);
+		default:
+			return -EINVAL;
+		}
+	case IIO_EV_DIR_FALLING:
+		switch (type) {
+		case IIO_EV_TYPE_THRESH:
+			return FIELD_GET(MAX30210_STATUS_TEMP_LO_MASK, val);
+		default:
+			return -EINVAL;
+		}
+	default:
+		return -EINVAL;
+	}
+}
+
+static int max30210_write_event_config(struct iio_dev *indio_dev,
+				       const struct iio_chan_spec *chan,
+				       enum iio_event_type type,
+				       enum iio_event_direction dir, bool state)
+{
+	struct max30210_state *st = iio_priv(indio_dev);
+	unsigned int mask;
+	int ret;
+
+	if (type != IIO_EV_TYPE_THRESH)
+		return -EINVAL;
+
+	switch (dir) {
+	case IIO_EV_DIR_RISING:
+		mask = MAX30210_STATUS_TEMP_HI_MASK;
+		break;
+	case IIO_EV_DIR_FALLING:
+		mask = MAX30210_STATUS_TEMP_LO_MASK;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	/*
+	 * Threshold events need the device sampling autonomously, independent
+	 * of whether the FIFO buffer is also enabled.
+	 */
+	if (state) {
+		ret = max30210_autoconv_get(st);
+		if (ret)
+			return ret;
+	}
+
+	ret = regmap_assign_bits(st->regmap, MAX30210_INT_EN_REG, mask, state);
+	if (ret) {
+		if (state)
+			max30210_autoconv_put(st);
+		return ret;
+	}
+
+	return state ? 0 : max30210_autoconv_put(st);
+}
+
+static int max30210_read_raw(struct iio_dev *indio_dev,
+			     struct iio_chan_spec const *chan, int *val,
+			     int *val2, long mask)
+{
+	struct max30210_state *st = iio_priv(indio_dev);
+	unsigned int uval;
+	int ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_SCALE:
+		*val = 5;
+		*val2 = MILLI;
+
+		return IIO_VAL_FRACTIONAL;
+	case IIO_CHAN_INFO_SAMP_FREQ: {
+		unsigned int period;
+
+		ret = regmap_read(st->regmap, MAX30210_TEMP_CONF_2_REG, &uval);
+		if (ret)
+			return ret;
+
+		period = FIELD_GET(MAX30210_TEMPCONF2_TEMP_PERIOD_MASK, uval);
+
+		/*
+		 * TEMP_PERIOD is an index into the sampling frequency lookup
+		 * table. Clamp in case the register holds a reserved value.
+		 */
+		if (period >= ARRAY_SIZE(max30210_samp_freq_avail))
+			period = ARRAY_SIZE(max30210_samp_freq_avail) - 1;
+
+		*val = max30210_samp_freq_avail[period][0];
+		*val2 = max30210_samp_freq_avail[period][1];
+
+		return IIO_VAL_INT_PLUS_MICRO;
+	}
+	case IIO_CHAN_INFO_RAW: {
+		IIO_DEV_ACQUIRE_DIRECT_MODE(indio_dev, claim);
+		if (IIO_DEV_ACQUIRE_FAILED(claim))
+			return -EBUSY;
+
+		guard(mutex)(&st->lock);
+
+		/*
+		 * TEMP_DATA_REG is only refreshed by a single-shot
+		 * conversion; the buffer/FIFO path is the only thing that
+		 * gets updated during AUTO mode. If AUTO is already running
+		 * for the buffer and/or events, triggering a one-off
+		 * conversion here would stomp the AUTO bit out from under
+		 * whoever enabled it, and there is no way to get a fresh
+		 * single-shot value without doing so -- refuse instead of
+		 * returning stale data.
+		 */
+		if (st->autoconv_users > 0)
+			return -EBUSY;
+
+		ret = regmap_write(st->regmap, MAX30210_TEMP_CONV_REG,
+				   MAX30210_TEMPCONV_CONV_T);
+		if (ret)
+			return ret;
+
+		/*
+		 * Wait until CONVERT_T auto-clears.
+		 * Datasheet:
+		 *   tBIAS_WU = 260 µs
+		 *   tINT     = 8 ms
+		 *
+		 * Worst-case conversion ≈ 8.26 ms.
+		 * Use 10 ms timeout for margin.
+		 */
+		ret = regmap_read_poll_timeout(st->regmap, MAX30210_TEMP_CONV_REG, uval,
+					       !(uval & MAX30210_TEMPCONV_CONV_T),
+					       500, 10 * USEC_PER_MSEC);
+		if (ret)
+			return ret;
+
+		return max30210_read_temp(st->regmap, MAX30210_TEMP_DATA_REG, val);
+	}
+	default:
+		return -EINVAL;
+	}
+}
+
+static int max30210_read_avail(struct iio_dev *indio_dev,
+			       struct iio_chan_spec const *chan,
+			       const int **vals, int *type, int *length,
+			       long mask)
+{
+	switch (mask) {
+	case IIO_CHAN_INFO_SAMP_FREQ:
+		*vals = &max30210_samp_freq_avail[0][0];
+		*type = IIO_VAL_INT_PLUS_MICRO;
+		*length = ARRAY_SIZE(max30210_samp_freq_avail) * 2;
+
+		return IIO_AVAIL_LIST;
+	default:
+		return -EINVAL;
+	}
+}
+
+static int max30210_write_raw(struct iio_dev *indio_dev,
+			      struct iio_chan_spec const *chan, int val,
+			      int val2, long mask)
+{
+	struct max30210_state *st = iio_priv(indio_dev);
+
+	switch (mask) {
+	case IIO_CHAN_INFO_SAMP_FREQ: {
+		if (val < 0 || val2 < 0)
+			return -EINVAL;
+
+		IIO_DEV_ACQUIRE_DIRECT_MODE(indio_dev, claim);
+		if (IIO_DEV_ACQUIRE_FAILED(claim))
+			return -EBUSY;
+
+		for (unsigned int i = 0; i < ARRAY_SIZE(max30210_samp_freq_avail); i++) {
+			if (val != max30210_samp_freq_avail[i][0] ||
+			    val2 != max30210_samp_freq_avail[i][1])
+				continue;
+
+			return regmap_update_bits(st->regmap, MAX30210_TEMP_CONF_2_REG,
+					MAX30210_TEMPCONF2_TEMP_PERIOD_MASK,
+					FIELD_PREP(MAX30210_TEMPCONF2_TEMP_PERIOD_MASK, i));
+		}
+
+		return -EINVAL;
+	}
+	default:
+		return -EINVAL;
+	}
+}
+
+static int max30210_set_watermark(struct iio_dev *indio_dev, unsigned int val)
+{
+	struct max30210_state *st = iio_priv(indio_dev);
+	int ret;
+
+	if (val < 1 || val > MAX30210_FIFO_SIZE)
+		return -EINVAL;
+
+	/*
+	 * FIFO_A_FULL sets the number of empty FIFO slots remaining when the
+	 * A_FULL interrupt fires. For a watermark of N samples, set
+	 * FIFO_A_FULL = FIFO_SIZE - N.
+	 */
+	ret = regmap_write(st->regmap, MAX30210_FIFO_CONF_1_REG,
+			   FIELD_PREP(MAX30210_FIFOCONF1_A_FULL_MASK,
+				      MAX30210_FIFO_SIZE - val));
+	if (ret)
+		return ret;
+
+	st->watermark = val;
+
+	return 0;
+}
+
+static ssize_t hwfifo_watermark_show(struct device *dev,
+				     struct device_attribute *devattr,
+				     char *buf)
+{
+	struct max30210_state *st = iio_priv(dev_to_iio_dev(dev));
+
+	return sysfs_emit(buf, "%d\n", st->watermark);
+}
+
+IIO_STATIC_CONST_DEVICE_ATTR(hwfifo_watermark_min, "1");
+IIO_STATIC_CONST_DEVICE_ATTR(hwfifo_watermark_max, __stringify(MAX30210_FIFO_SIZE));
+static IIO_DEVICE_ATTR_RO(hwfifo_watermark, 0);
+
+static const struct iio_dev_attr *max30210_fifo_attributes[] = {
+	&iio_dev_attr_hwfifo_watermark_min,
+	&iio_dev_attr_hwfifo_watermark_max,
+	&iio_dev_attr_hwfifo_watermark,
+	NULL
+};
+
+static int max30210_buffer_preenable(struct iio_dev *indio_dev)
+{
+	struct max30210_state *st = iio_priv(indio_dev);
+	int ret;
+
+	/* Enable FIFO-full interrupt */
+	ret = regmap_set_bits(st->regmap, MAX30210_INT_EN_REG,
+			      MAX30210_STATUS_A_FULL_MASK);
+	if (ret)
+		return ret;
+
+	/* Flush FIFO before starting autonomous conversions */
+	ret = regmap_set_bits(st->regmap, MAX30210_FIFO_CONF_2_REG,
+			      MAX30210_FIFOCONF2_FLUSH_FIFO);
+	if (ret)
+		return ret;
+
+	return max30210_autoconv_get(st);
+}
+
+static int max30210_buffer_postdisable(struct iio_dev *indio_dev)
+{
+	struct max30210_state *st = iio_priv(indio_dev);
+	int ret;
+
+	ret = max30210_autoconv_put(st);
+	if (ret)
+		return ret;
+
+	/* Flush FIFO */
+	ret = regmap_set_bits(st->regmap, MAX30210_FIFO_CONF_2_REG,
+			      MAX30210_FIFOCONF2_FLUSH_FIFO);
+	if (ret)
+		return ret;
+
+	/* Disable FIFO-full interrupt */
+	return regmap_clear_bits(st->regmap, MAX30210_INT_EN_REG,
+				 MAX30210_STATUS_A_FULL_MASK);
+}
+
+static const struct iio_buffer_setup_ops max30210_buffer_ops = {
+	.preenable = max30210_buffer_preenable,
+	.postdisable = max30210_buffer_postdisable,
+};
+
+static const struct iio_info max30210_info = {
+	.read_raw = max30210_read_raw,
+	.read_avail = max30210_read_avail,
+	.write_raw = max30210_write_raw,
+	.hwfifo_set_watermark = max30210_set_watermark,
+	.debugfs_reg_access = max30210_reg_access,
+	.read_event_value = max30210_read_event,
+	.write_event_value = max30210_write_event,
+	.write_event_config = max30210_write_event_config,
+	.read_event_config = max30210_read_event_config,
+};
+
+static const struct iio_event_spec max30210_events[] = {
+	{
+		.type = IIO_EV_TYPE_THRESH,
+		.dir = IIO_EV_DIR_RISING,
+		.mask_separate = BIT(IIO_EV_INFO_VALUE) | BIT(IIO_EV_INFO_ENABLE),
+	}, {
+		.type = IIO_EV_TYPE_THRESH,
+		.dir = IIO_EV_DIR_FALLING,
+		.mask_separate = BIT(IIO_EV_INFO_VALUE) | BIT(IIO_EV_INFO_ENABLE),
+	},
+};
+
+static const struct iio_chan_spec max30210_channel = {
+	.type = IIO_TEMP,
+	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+			      BIT(IIO_CHAN_INFO_SCALE) |
+			      BIT(IIO_CHAN_INFO_SAMP_FREQ),
+	.info_mask_separate_available = BIT(IIO_CHAN_INFO_SAMP_FREQ),
+	.scan_index = 0,
+	.event_spec = max30210_events,
+	.num_event_specs = ARRAY_SIZE(max30210_events),
+	.scan_type = {
+		.sign = 's',
+		.realbits = 16,
+		.storagebits = 16,
+		.endianness = IIO_CPU,
+	},
+};
+
+static void max30210_powerdown(void *data)
+{
+	struct gpio_desc *powerdown_gpio = data;
+
+	gpiod_set_value(powerdown_gpio, 1);
+}
+
+static int max30210_setup(struct max30210_state *st, struct device *dev)
+{
+	struct gpio_desc *powerdown_gpio;
+	unsigned int val;
+	int ret;
+
+	powerdown_gpio = devm_gpiod_get_optional(dev, "powerdown",
+						 GPIOD_OUT_HIGH);
+	if (IS_ERR(powerdown_gpio))
+		return dev_err_probe(dev, PTR_ERR(powerdown_gpio),
+				     "failed to request powerdown GPIO\n");
+
+	if (powerdown_gpio) {
+		/* Deassert powerdown to power up device */
+		gpiod_set_value(powerdown_gpio, 0);
+
+		ret = devm_add_action_or_reset(dev, max30210_powerdown, powerdown_gpio);
+		if (ret)
+			return ret;
+	} else {
+		ret = regmap_set_bits(st->regmap, MAX30210_SYS_CONF_REG,
+				      MAX30210_SYSCONF_RESET);
+		if (ret)
+			return ret;
+	}
+
+	/*
+	 * Datasheet Figure 6:
+	 * tPU max = 700 µs after power-up or reset before device is ready.
+	 */
+	fsleep(700);
+
+	/* Clear status byte */
+	return regmap_read(st->regmap, MAX30210_STATUS_REG, &val);
+}
+
+static int max30210_probe(struct i2c_client *client)
+{
+	struct device *dev = &client->dev;
+	struct iio_dev *indio_dev;
+	struct max30210_state *st;
+	int ret;
+
+	indio_dev = devm_iio_device_alloc(dev, sizeof(*st));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	st = iio_priv(indio_dev);
+	mutex_init(&st->lock);
+
+	ret = devm_regulator_get_enable(dev, "vdd");
+	if (ret)
+		return dev_err_probe(dev, ret,
+				     "Failed to enable vdd regulator.\n");
+
+	st->regmap = devm_regmap_init_i2c(client, &max30210_regmap);
+	if (IS_ERR(st->regmap))
+		return dev_err_probe(dev, PTR_ERR(st->regmap),
+				     "Failed to allocate regmap.\n");
+
+	st->watermark = MAX30210_WATERMARK_DEFAULT;
+
+	ret = max30210_setup(st, dev);
+	if (ret)
+		return ret;
+
+	indio_dev->modes = INDIO_DIRECT_MODE;
+	indio_dev->channels = &max30210_channel;
+	indio_dev->num_channels = 1;
+	indio_dev->name = "max30210";
+	indio_dev->info = &max30210_info;
+
+	/* Without an interrupt there is no way to drain the FIFO into the buffer */
+	if (client->irq) {
+		ret = devm_iio_kfifo_buffer_setup_ext(dev, indio_dev, &max30210_buffer_ops,
+						      max30210_fifo_attributes);
+		if (ret)
+			return ret;
+	}
+
+	ret = devm_iio_device_register(dev, indio_dev);
+	if (ret)
+		return ret;
+
+	if (!client->irq)
+		return 0;
+
+	/*
+	 * Request the IRQ after registering the IIO device so devm tears it
+	 * down first on removal, before the event interface is freed.
+	 */
+	return devm_request_threaded_irq(dev, client->irq, NULL,
+					 max30210_irq_handler, IRQF_ONESHOT,
+					 indio_dev->name, indio_dev);
+}
+
+static const struct i2c_device_id max30210_id[] = {
+	{ "max30210" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, max30210_id);
+
+static const struct of_device_id max30210_of_match[] = {
+	{ .compatible = "adi,max30210" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, max30210_of_match);
+
+static struct i2c_driver max30210_driver = {
+	.driver = {
+		.name = "max30210",
+		.of_match_table = max30210_of_match,
+	},
+	.probe = max30210_probe,
+	.id_table = max30210_id,
+};
+module_i2c_driver(max30210_driver);
+
+MODULE_AUTHOR("John Erasmus Mari Geronimo <johnerasmusmari.geronimo@analog.com>");
+MODULE_DESCRIPTION("MAX30210 low-power digital temperature sensor");
+MODULE_LICENSE("GPL");
-- 
2.34.1

Re: [PATCH v4 1/2] dt-bindings: iio: temperature: add ADI MAX30210

[Rob Herring]

On Thu, Oct 15, 2026 at 09:21:58AM +0800, John Erasmus Mari Geronimo wrote:
> Add device tree binding documentation for the Analog Devices
> MAX30210 temperature sensor.
> 
> Signed-off-by: John Erasmus Mari Geronimo <johnerasmusmari.geronimo@analog.com>

Missing Krzysztof's Reviewed-by.

Re: [PATCH v4 2/2] iio: temperature: add support for Analog Devices MAX30210

[Joshua Crofts]

On Thu, 15 Oct 2026 09:21:59 +0800
John Erasmus Mari Geronimo <johnerasmusmari.geronimo@analog.com> wrote:

> Add support for the Analog Devices MAX30210 I2C temperature
> sensor.
> 
> The driver uses regmap for register access and integrates with
> the IIO framework. It supports:
> 
> - Direct mode temperature conversion
> - Configurable sampling frequency
> - Threshold events
> - FIFO operation with IIO kfifo buffer support
> - Optional interrupt-driven data ready signaling
> 
> The device provides 16-bit signed temperature data and a
> 64-sample FIFO.
> 
> Signed-off-by: John Erasmus Mari Geronimo <johnerasmusmari.geronimo@analog.com>
> ---

Hi, quick review from me. Please also check out Sashiko's remarks:

https://sashiko.dev/#/patchset/20261015012159.44-1-johnerasmusmari.geronimo%40analog.com

Josh

> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Analog Devices MAX30210 I2C Temperature Sensor driver
> + *
> + * Copyright 2026 Analog Devices Inc.

Adding a link to the datasheet here would be good.

> + */
> +
> +#include <linux/array_size.h>
> +#include <linux/bitfield.h>
> +#include <linux/bitops.h>
> +#include <linux/delay.h>
> +#include <linux/gpio/consumer.h>
> +#include <linux/i2c.h>
> +#include <linux/iio/buffer.h>
> +#include <linux/iio/events.h>
> +#include <linux/iio/iio.h>
> +#include <linux/iio/kfifo_buf.h>
> +#include <linux/iio/sysfs.h>

Please separate the <linux/iio/*> specific headers from the
generic linux headers.

> +#include <linux/mutex.h>
> +#include <linux/regmap.h>
> +#include <linux/regulator/consumer.h>
> +#include <linux/time.h>
> +#include <linux/types.h>
> +#include <linux/unaligned.h>
> +#include <linux/units.h>

Missing cleanup.h, sysfs.h and asm/byteorder.h.

> +
> +#define MAX30210_STATUS_REG			0x00
> +#define   MAX30210_STATUS_A_FULL_MASK		BIT(7)
> +#define   MAX30210_STATUS_TEMP_RDY_MASK	BIT(6)
> +#define   MAX30210_STATUS_TEMP_DEC_MASK	BIT(5)
> +#define   MAX30210_STATUS_TEMP_INC_MASK	BIT(4)
> +#define   MAX30210_STATUS_TEMP_LO_MASK		BIT(3)
> +#define   MAX30210_STATUS_TEMP_HI_MASK		BIT(2)
> +#define   MAX30210_STATUS_PWR_RDY		BIT(0)
> +#define MAX30210_INT_EN_REG			0x02
> +#define MAX30210_FIFO_DATA_REG			0x08
> +#define MAX30210_FIFO_CONF_1_REG		0x09
> +#define   MAX30210_FIFOCONF1_A_FULL_MASK	GENMASK(5, 0)
> +#define MAX30210_FIFO_CONF_2_REG		0x0A
> +#define   MAX30210_FIFOCONF2_FLUSH_FIFO		BIT(4)
> +#define MAX30210_SYS_CONF_REG			0x11
> +#define   MAX30210_SYSCONF_RESET		BIT(0)
> +#define MAX30210_PIN_CONF_REG			0x12
> +#define   MAX30210_PINCONF_EXT_CNV_EN		BIT(7)
> +#define   MAX30210_PINCONF_EXT_CVT_ICFG		BIT(6)
> +#define   MAX30210_PINCONF_INT_FCFG_MASK	GENMASK(3, 2)
> +#define   MAX30210_PINCONF_INT_OCFG_MASK	GENMASK(1, 0)
> +#define MAX30210_TEMP_ALM_HI_REG		0x22
> +#define MAX30210_TEMP_ALM_LO_REG		0x24
> +#define MAX30210_TEMP_INC_THRESH_REG		0x26
> +#define MAX30210_TEMP_DEC_THRESH_REG		0x27
> +#define MAX30210_TEMP_CONF_1_REG		0x28
> +#define   MAX30210_TEMPCONF1_CHG_DET_EN		BIT(3)
> +#define   MAX30210_TEMPCONF1_RATE_CHG_FILTER_MASK	GENMASK(2, 0)
> +#define MAX30210_TEMP_CONF_2_REG		0x29
> +#define   MAX30210_TEMPCONF2_TEMP_PERIOD_MASK	GENMASK(3, 0)
> +#define   MAX30210_TEMPCONF2_ALERT_MODE		BIT(7)
> +#define MAX30210_TEMP_CONV_REG			0x2A
> +#define   MAX30210_TEMPCONV_CONV_T		BIT(0)
> +#define   MAX30210_TEMPCONV_AUTO		BIT(1)
> +#define MAX30210_TEMP_DATA_REG			0x2B
> +#define MAX30210_TEMP_SLOPE_REG			0x2D
> +#define MAX30210_UNIQUE_ID_REG			0x30
> +#define MAX30210_PART_ID_REG			0xFF
> +
> +#define MAX30210_PART_ID			0x45
> +#define MAX30210_FIFO_SIZE			64
> +#define MAX30210_FIFO_BYTES_PER_SAMPLE		3
> +#define MAX30210_FIFO_TEMP_MASK			GENMASK(15, 0)
> +#define MAX30210_FIFO_INVAL_DATA		GENMASK(23, 0)
> +#define MAX30210_WATERMARK_DEFAULT		(0x40 - 0x1F)
> +
> +#define MAX30210_UNIQUE_ID_LEN			6
> +#define MAX30210_EXT_CVT_FREQ_MIN		1
> +#define MAX30210_EXT_CVT_FREQ_MAX		20
> +
> +struct max30210_state {
> +	struct regmap *regmap;
> +	/* Raw FIFO byte buffer */
> +	u8 fifo_buf[MAX30210_FIFO_BYTES_PER_SAMPLE * MAX30210_FIFO_SIZE];
> +	/* Protects autoconv_users and the autonomous-conversion enable bit */
> +	struct mutex lock;
> +	unsigned int autoconv_users;
> +	u8 watermark;

Does pahole agree with this layout?

> +};
> +
> +static const int max30210_samp_freq_avail[][2] = {
> +	{ 0, 15625 },
> +	{ 0, 31250 },
> +	{ 0, 62500 },
> +	{ 0, 125000 },
> +	{ 0, 250000 },
> +	{ 0, 500000 },
> +	{ 1, 0 },
> +	{ 2, 0 },
> +	{ 4, 0 },
> +	{ 8, 0 },
> +};
> +

...

> +static int max30210_read_raw(struct iio_dev *indio_dev,
> +			     struct iio_chan_spec const *chan, int *val,

Small nit, but ideally have val, val2 and mask on the same line for
readability reasons. This goes for all instances of this in the driver.

> +			     int *val2, long mask)
> +{
> +	struct max30210_state *st = iio_priv(indio_dev);
> +	unsigned int uval;
> +	int ret;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_SCALE:
> +		*val = 5;
> +		*val2 = MILLI;
> +
> +		return IIO_VAL_FRACTIONAL;
> +	case IIO_CHAN_INFO_SAMP_FREQ: {
> +		unsigned int period;
> +
> +		ret = regmap_read(st->regmap, MAX30210_TEMP_CONF_2_REG, &uval);
> +		if (ret)
> +			return ret;
> +
> +		period = FIELD_GET(MAX30210_TEMPCONF2_TEMP_PERIOD_MASK, uval);
> +
> +		/*
> +		 * TEMP_PERIOD is an index into the sampling frequency lookup
> +		 * table. Clamp in case the register holds a reserved value.
> +		 */
> +		if (period >= ARRAY_SIZE(max30210_samp_freq_avail))
> +			period = ARRAY_SIZE(max30210_samp_freq_avail) - 1;
> +
> +		*val = max30210_samp_freq_avail[period][0];
> +		*val2 = max30210_samp_freq_avail[period][1];
> +
> +		return IIO_VAL_INT_PLUS_MICRO;
> +	}

...

> +
> +static int max30210_probe(struct i2c_client *client)
> +{
> +	struct device *dev = &client->dev;
> +	struct iio_dev *indio_dev;
> +	struct max30210_state *st;
> +	int ret;
> +
> +	indio_dev = devm_iio_device_alloc(dev, sizeof(*st));
> +	if (!indio_dev)
> +		return -ENOMEM;
> +
> +	st = iio_priv(indio_dev);
> +	mutex_init(&st->lock);

devm_mutex_init() + check return value.

> +
> +	ret = devm_regulator_get_enable(dev, "vdd");
> +	if (ret)
> +		return dev_err_probe(dev, ret,
> +				     "Failed to enable vdd regulator.\n");
> +
> +	st->regmap = devm_regmap_init_i2c(client, &max30210_regmap);
> +	if (IS_ERR(st->regmap))
> +		return dev_err_probe(dev, PTR_ERR(st->regmap),
> +				     "Failed to allocate regmap.\n");
> +
> +	st->watermark = MAX30210_WATERMARK_DEFAULT;
> +
> +	ret = max30210_setup(st, dev);
> +	if (ret)
> +		return ret;
> +
> +	indio_dev->modes = INDIO_DIRECT_MODE;
> +	indio_dev->channels = &max30210_channel;
> +	indio_dev->num_channels = 1;
> +	indio_dev->name = "max30210";
> +	indio_dev->info = &max30210_info;
> +
> +	/* Without an interrupt there is no way to drain the FIFO into the buffer */
> +	if (client->irq) {
> +		ret = devm_iio_kfifo_buffer_setup_ext(dev, indio_dev, &max30210_buffer_ops,
> +						      max30210_fifo_attributes);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	ret = devm_iio_device_register(dev, indio_dev);
> +	if (ret)
> +		return ret;
> +
> +	if (!client->irq)
> +		return 0;
> +
> +	/*
> +	 * Request the IRQ after registering the IIO device so devm tears it
> +	 * down first on removal, before the event interface is freed.
> +	 */
> +	return devm_request_threaded_irq(dev, client->irq, NULL,
> +					 max30210_irq_handler, IRQF_ONESHOT,
> +					 indio_dev->name, indio_dev);
> +}
> +
> +static const struct i2c_device_id max30210_id[] = {
> +	{ "max30210" },

C99 initializers please.

-- 
Kind regards,
Joshua Crofts

Re: [PATCH v4 0/2] Add support for Analog Devices MAX30210

[Joshua Crofts]

On Thu, 15 Oct 2026 09:21:57 +0800
John Erasmus Mari Geronimo <johnerasmusmari.geronimo@analog.com> wrote:

> This series adds support for the Analog Devices MAX30210 I2C
> temperature sensor.
> 
> The device provides a 16-bit temperature output and includes
> features such as a hardware FIFO, programmable sampling rate,
> threshold alarms, and interrupt support. These capabilities map
> naturally to the IIO subsystem, particularly the buffered interface
> and event framework -- hwmon has no equivalent buffered-capture
> framework, and its alarm attributes are polled rather than
> interrupt-driven, so there is no path to supporting the FIFO or the
> autonomous threshold comparators there.
> 
> Although the MAX30210 belongs to the same device family as the
> MAX30208, it is implemented as a separate driver. The MAX30210 has
> a significantly different feature set, including a 64-sample hardware
> FIFO with configurable watermark interrupts, programmable sampling
> rates, and event support. These features require buffered operation
> and IRQ-driven data handling which are not present in the MAX30208
> driver (which talks to the device directly via i2c_smbus_*() calls
> with no regmap, and has no IIO buffer or event interface at all).
> 
> In addition, the MAX30210 uses a different register map and a more
> flexible I2C address selection scheme. Supporting both devices in a
> single driver would introduce substantial conditional logic, so a
> separate driver keeps the implementation simpler and easier to
> maintain.
> 
> Patch 1 adds the devicetree binding.
> Patch 2 adds the IIO driver implementation.

Please send a link to the datasheet next time, it saves time and at
least we know which version to base reviews on.

I believe Andy also asked to to add a Datasheet tag to the commits.

Q to others: should we try to make the Datasheet tag official?

-- 
Kind regards,
Joshua Crofts