[PATCH v5 0/2] iio: adc: add MAX40080 current-sense amplifier driver

[PATCH v5 0/2] iio: adc: add MAX40080 current-sense amplifier driver

[Stefan Popa]

This series adds support for the MAX40080, a bidirectional current-sense
amplifier with an integrated 12-bit ADC.

The driver is placed in IIO rather than hwmon because:
  - IIO's scale/raw model naturally exposes the selectable gain ranges and
    lets userspace apply the correct scale per range.
  - Buffered capture support is planned for a follow-up series -- each
    conversion returns a matched current+voltage pair, which maps cleanly
    to IIO's buffered/triggered model.

Changes since v4:
  - Initialize tmp = 0 in max40080_read_iv() before read_poll_timeout to
    avoid using potentially uninitialized value in the condition check
    (Sashiko, Jonathan).
  - Simplify max40080_get_oversampling_ratio() to use cached value instead
    of reading from the device (Jonathan).
  - Remove DMA-safe buffer from struct -- I2C layer already bounces data
    internally for i2c_smbus_* calls (Jonathan).
  - Make shunt-resistor-micro-ohms required in DT binding. The default
    1 Ohm was arbitrary and rarely correct for real hardware (Jonathan).
  - Remove PM ops entirely. Having only resume without suspend was flagged
    as "papering over" possible power loss issues (Jonathan).
  - Remove the {} scope around propname, declare it at function top (Andy).
  - Remove mod_devicetable.h include -- i2c.h provides necessary types
    (Jonathan).

Changes since v3:
  - Removed all regmap usage -- regmap doesn't support SMBus PEC or Quick
    Command, both required by this device (Nuno).
  - Fixed locking: max40080_update_bits() now takes the lock internally,
    and callers update cached state after the call returns (Nuno).
  - Consistent comment style: capital first letter + period (Andy).
  - Use propname variable to deduplicate "shunt-resistor-micro-ohms" (Andy).
  - Return IIO_VAL_* inline instead of break + return pattern (Nuno).

Changes since v2:
  - Added shunt-resistor-micro-ohms DT property with default value.
  - Use single-shot mode with SMBus Quick Command trigger for correlated
    current/voltage reads.
  - Precompute current scale per range at probe time.

Link: https://lore.kernel.org/linux-iio/20260717123852.1140893-1-stefan.popa@analog.com/ [v4]
Link: https://lore.kernel.org/linux-iio/20260715063652.368501-1-stefan.popa@analog.com/ [v3]
Link: https://lore.kernel.org/linux-iio/20260713120226.90303-1-stefan.popa@analog.com/ [v2]
Link: https://lore.kernel.org/linux-iio/20260703102941.1141341-1-stefan.popa@analog.com/ [v1]

Stefan Popa (2):
  dt-bindings: iio: adc: add maxim,max40080
  iio: adc: add MAX40080 current-sense amplifier driver

 .../bindings/iio/adc/maxim,max40080.yaml      |  56 ++
 MAINTAINERS                                   |   9 +
 drivers/iio/adc/Kconfig                       |  11 +
 drivers/iio/adc/Makefile                      |   1 +
 drivers/iio/adc/max40080.c                    | 586 ++++++++++++++++++
 5 files changed, 663 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/adc/maxim,max40080.yaml
 create mode 100644 drivers/iio/adc/max40080.c

--
2.53.0

[PATCH v5 1/2] dt-bindings: iio: adc: add maxim,max40080

[Stefan Popa]

Add device tree bindings for the Maxim MAX40080 bidirectional
current-sense amplifier with a 12-bit ADC and an I2C/SMBus interface.

Signed-off-by: Stefan Popa <stefan.popa@analog.com>
---
 .../bindings/iio/adc/maxim,max40080.yaml      | 56 +++++++++++++++++++
 1 file changed, 56 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/adc/maxim,max40080.yaml

diff --git a/Documentation/devicetree/bindings/iio/adc/maxim,max40080.yaml b/Documentation/devicetree/bindings/iio/adc/maxim,max40080.yaml
new file mode 100644
index 0000000000000..170bf4eff8706
--- /dev/null
+++ b/Documentation/devicetree/bindings/iio/adc/maxim,max40080.yaml
@@ -0,0 +1,56 @@
+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/adc/maxim,max40080.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Maxim MAX40080 bidirectional current-sense amplifier
+
+maintainers:
+  - Ciprian Hegbeli <ciprian.hegbeli@analog.com>
+  - Stefan Popa <stefan.popa@analog.com>
+
+description: |
+  The MAX40080 is a high-precision, bidirectional current-sense amplifier with
+  an integrated 12-bit ADC and an I2C/SMBus interface. It measures the voltage
+  across an external shunt resistor and the input bus voltage, and stores the
+  results in an internal FIFO.
+
+  Datasheet:
+    https://www.analog.com/en/products/max40080.html
+
+properties:
+  compatible:
+    const: maxim,max40080
+
+  reg:
+    maxItems: 1
+
+  "#io-channel-cells":
+    const: 1
+
+  shunt-resistor-micro-ohms:
+    description:
+      Value of the current-sense shunt resistor connected between the IN+ and
+      IN- inputs. Used to scale the reported current.
+
+required:
+  - compatible
+  - reg
+  - shunt-resistor-micro-ohms
+
+additionalProperties: false
+
+examples:
+  - |
+    i2c {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        adc@20 {
+            compatible = "maxim,max40080";
+            reg = <0x20>;
+            #io-channel-cells = <1>;
+            shunt-resistor-micro-ohms = <100000>;
+        };
+    };
-- 
2.53.0

[PATCH v5 2/2] iio: adc: add MAX40080 current-sense amplifier driver

[Stefan Popa]

The MAX40080 is a bidirectional current-sense amplifier with an
integrated 12-bit ADC and an I2C/SMBus interface. It measures the
voltage across an external shunt resistor and the input bus voltage,
storing the results in an internal FIFO.

Add a direct-mode IIO driver exposing the current and voltage channels
with raw, scale and hardware-gain attributes, a configurable
oversampling (digital averaging) ratio, and PEC-protected register
access. The current scale is derived from the shunt resistor value
described in the device tree.

Signed-off-by: Ciprian Hegbeli <ciprian.hegbeli@analog.com>
Signed-off-by: Stefan Popa <stefan.popa@analog.com>
---
 MAINTAINERS                |   9 +
 drivers/iio/adc/Kconfig    |  11 +
 drivers/iio/adc/Makefile   |   1 +
 drivers/iio/adc/max40080.c | 586 +++++++++++++++++++++++++++++++++++++
 4 files changed, 607 insertions(+)
 create mode 100644 drivers/iio/adc/max40080.c

diff --git a/MAINTAINERS b/MAINTAINERS
index e087673237636..f50c1e00e12bb 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -15513,6 +15513,15 @@ L:	linux-iio@vger.kernel.org
 S:	Supported
 F:	drivers/iio/temperature/max30208.c
 
+MAXIM MAX40080 CURRENT SENSE AMPLIFIER DRIVER
+M:	Ciprian Hegbeli <ciprian.hegbeli@analog.com>
+M:	Stefan Popa <stefan.popa@analog.com>
+L:	linux-iio@vger.kernel.org
+S:	Supported
+W:	https://ez.analog.com/linux-software-drivers
+F:	Documentation/devicetree/bindings/iio/adc/maxim,max40080.yaml
+F:	drivers/iio/adc/max40080.c
+
 MAXIM MAX7360 KEYPAD LED MFD DRIVER
 M:	Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
 S:	Maintained
diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
index 58da8255525e4..b651c57bbc3f5 100644
--- a/drivers/iio/adc/Kconfig
+++ b/drivers/iio/adc/Kconfig
@@ -1041,6 +1041,17 @@ config MAX34408
 	  To compile this driver as a module, choose M here: the module will be
 	  called max34408.
 
+config MAX40080
+	tristate "Analog Devices MAX40080 Current Sense Amplifier"
+	depends on I2C
+	help
+	  Say yes here to build support for the Analog Devices MAX40080
+	  bidirectional current-sense amplifier with a 12-bit ADC and an I2C
+	  interface.
+
+	  To compile this driver as a module, choose M here: the module will be
+	  called max40080.
+
 config MAX77541_ADC
 	tristate "Analog Devices MAX77541 ADC driver"
 	depends on MFD_MAX77541
diff --git a/drivers/iio/adc/Makefile b/drivers/iio/adc/Makefile
index 7cc8f9a12f763..e1953353c68a4 100644
--- a/drivers/iio/adc/Makefile
+++ b/drivers/iio/adc/Makefile
@@ -91,6 +91,7 @@ obj-$(CONFIG_MAX1241) += max1241.o
 obj-$(CONFIG_MAX1363) += max1363.o
 obj-$(CONFIG_MAX14001) += max14001.o
 obj-$(CONFIG_MAX34408) += max34408.o
+obj-$(CONFIG_MAX40080) += max40080.o
 obj-$(CONFIG_MAX77541_ADC) += max77541-adc.o
 obj-$(CONFIG_MAX9611) += max9611.o
 obj-$(CONFIG_MCP320X) += mcp320x.o
diff --git a/drivers/iio/adc/max40080.c b/drivers/iio/adc/max40080.c
new file mode 100644
index 0000000000000..cdf626dccb24f
--- /dev/null
+++ b/drivers/iio/adc/max40080.c
@@ -0,0 +1,586 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * MAX40080 Digital Current-Sense Amplifier driver
+ *
+ * Copyright 2026 Analog Devices, Inc.
+ */
+
+#include <linux/bitfield.h>
+#include <linux/bitops.h>
+#include <linux/cleanup.h>
+#include <linux/i2c.h>
+#include <linux/iopoll.h>
+#include <linux/math64.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/property.h>
+#include <linux/unaligned.h>
+#include <linux/units.h>
+
+#include <linux/iio/iio.h>
+
+#define MAX40080_REG_CFG		0x00
+#define  MAX40080_MODE_MSK		GENMASK(2, 0)
+#define  MAX40080_PEC_EN_MSK		BIT(5)
+#define  MAX40080_RANGE_MSK		BIT(6)
+#define  MAX40080_FILTER_MSK		GENMASK(14, 12)
+
+#define MAX40080_REG_FIFO_CFG		0x0A
+#define  MAX40080_STORE_IV_MSK		GENMASK(1, 0)
+
+#define MAX40080_REG_IV			0x10
+/* Current is a 13-bit two's-complement value (magnitude + sign bit). */
+#define  MAX40080_IV_I_MSK		GENMASK(12, 0)
+#define  MAX40080_IV_I_SIGN_BIT		12
+#define  MAX40080_IV_V_MAG_MSK		GENMASK(27, 16)
+#define  MAX40080_IV_VALID_MSK		BIT(31)
+
+/* CFG.mode field */
+#define MAX40080_STDBY_MODE		0x00
+#define MAX40080_SINGLE_MODE		0x02	/* one conversion per Quick Command */
+
+/* FIFO_CFG.store_iv field */
+#define MAX40080_STORE_I_V		0x02
+
+#define MAX40080_ADC_RES		4096
+#define MAX40080_INTER_VREF_MV		1250
+#define MAX40080_V_BUFF_GAIN		30
+#define MAX40080_CSA_50MV_GAIN		25
+#define MAX40080_CSA_10MV_GAIN		125
+
+/*
+ * The RANGE field (CFG bit 6) selects one of two current-sense full-scale
+ * ranges (the MAX40080 supports exactly two: +/-50 mV and +/-10 mV). Ordered
+ * so that the array index equals the RANGE field value: index 0 = 50 mV range
+ * (gain 25 V/V), index 1 = 10 mV range (gain 125 V/V).
+ */
+static const int max40080_csa_gain[] = {
+	MAX40080_CSA_50MV_GAIN, MAX40080_CSA_10MV_GAIN,
+};
+
+#define MAX40080_NUM_RANGES	ARRAY_SIZE(max40080_csa_gain)
+
+struct max40080_state {
+	struct i2c_client *client;
+	/* Serializes read-modify-write access to the CFG register. */
+	struct mutex lock;
+	u32 shunt_resistor_uohm;
+	/* Cached configuration: the selected RANGE index and oversampling ratio. */
+	unsigned int range;
+	int oversampling_ratio;
+	/*
+	 * Precomputed current scale (mA per code) for each RANGE setting, as
+	 * {integer, nano} pairs for IIO_VAL_INT_PLUS_NANO. The range is
+	 * selected by writing the corresponding scale.
+	 */
+	int current_scale[MAX40080_NUM_RANGES][2];
+};
+
+static const int max40080_oversampling_avail[] = { 1, 8, 16, 32, 64, 128 };
+
+static int max40080_update_bits(struct max40080_state *st, u8 reg,
+				u16 mask, u16 val)
+{
+	int ret;
+	int tmp;
+
+	guard(mutex)(&st->lock);
+
+	tmp = i2c_smbus_read_word_data(st->client, reg);
+	if (tmp < 0)
+		return tmp;
+
+	tmp &= ~mask;
+	tmp |= val & mask;
+
+	ret = i2c_smbus_write_word_data(st->client, reg, tmp);
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+
+/*
+ * In single-measurement mode the device sits idle until it receives an SMBus
+ * Quick Command, then performs exactly one current and one voltage conversion
+ * and returns to idle. Triggering on demand this way (rather than running the
+ * FIFO continuously in active mode) means each read returns a fresh, coherent
+ * current/voltage pair instead of the oldest queued FIFO entry.
+ */
+static int max40080_trigger_measurement(struct max40080_state *st)
+{
+	return i2c_smbus_xfer(st->client->adapter, st->client->addr,
+			      st->client->flags, I2C_SMBUS_WRITE, 0,
+			      I2C_SMBUS_QUICK, NULL);
+}
+
+/*
+ * A single measurement holds the matched current/voltage pair in one 32-bit
+ * word (MAX40080_REG_IV). Reading all four bytes in one transaction returns
+ * both from the same conversion; reading the separate current (0x0C) and
+ * voltage (0x0E) registers would decorrelate the two channels.
+ *
+ * Unlike the word accesses used elsewhere, this is a plain I2C block read: the
+ * SMBus layer does not append or verify a PEC byte for it even when PEC is
+ * otherwise enabled for the device, so this transfer is not PEC protected.
+ */
+static int max40080_read_iv_once(struct max40080_state *st, u32 *iv)
+{
+	u8 buf[4];
+	int ret;
+
+	ret = i2c_smbus_read_i2c_block_data(st->client, MAX40080_REG_IV,
+					    sizeof(buf), buf);
+	if (ret < 0)
+		return ret;
+	if (ret != sizeof(buf))
+		return -EIO;
+
+	*iv = get_unaligned_le32(buf);
+
+	return 0;
+}
+
+static int max40080_read_iv(struct max40080_state *st, u32 *iv)
+{
+	u32 tmp = 0;
+	int ret, io_ret;
+
+	guard(mutex)(&st->lock);
+
+	ret = max40080_trigger_measurement(st);
+	if (ret < 0)
+		return ret;
+
+	/*
+	 * Wait for the conversion to complete by polling the FIFO valid bit
+	 * (or bail out on an I2C error). Polling the device's own status makes
+	 * this independent of the actual conversion time, which varies with the
+	 * oversampling ratio and the bus speed. The timeout is only a safety
+	 * ceiling: the worst case is the maximum 128x averaging on both the
+	 * current and voltage channels at the slowest 15 ksps base rate plus the
+	 * inter-channel switching time, i.e. roughly 20 ms; 50 ms leaves ample
+	 * margin.
+	 */
+	ret = read_poll_timeout(max40080_read_iv_once, io_ret,
+				io_ret || (tmp & MAX40080_IV_VALID_MSK),
+				500, 50000, false, st, &tmp);
+	*iv = tmp;
+	if (ret)
+		return ret;
+
+	return io_ret;
+}
+
+static int max40080_get_current(struct max40080_state *st, int *val)
+{
+	u32 iv = 0;
+	int ret;
+
+	ret = max40080_read_iv(st, &iv);
+	if (ret)
+		return ret;
+
+	*val = sign_extend32(FIELD_GET(MAX40080_IV_I_MSK, iv),
+			     MAX40080_IV_I_SIGN_BIT);
+
+	return 0;
+}
+
+static int max40080_get_voltage(struct max40080_state *st, int *val)
+{
+	u32 iv = 0;
+	int ret;
+
+	ret = max40080_read_iv(st, &iv);
+	if (ret)
+		return ret;
+
+	*val = FIELD_GET(MAX40080_IV_V_MAG_MSK, iv);
+
+	return 0;
+}
+
+static int max40080_set_range(struct max40080_state *st, unsigned int range)
+{
+	int ret;
+
+	ret = max40080_update_bits(st, MAX40080_REG_CFG, MAX40080_RANGE_MSK,
+				   FIELD_PREP(MAX40080_RANGE_MSK, range));
+	if (ret)
+		return ret;
+
+	st->range = range;
+
+	return 0;
+}
+
+/*
+ * Precompute the current scale (mA per code) for each RANGE setting as
+ * {integer, nano} pairs. The shunt drop for a full-scale code is
+ *   Vref[mV] / (ADC_RES * gain)
+ * and current = Vshunt / Rshunt, so with Rshunt in micro-ohms the scale in
+ * mA/code is
+ *   Vref[mV] * NANO * MICRO / (ADC_RES * gain * Rshunt[uohm])
+ * expressed as an integer part plus a nano fractional part.
+ */
+static void max40080_calc_current_scale(struct max40080_state *st)
+{
+	unsigned int i;
+	u32 rem;
+	u64 tmp;
+
+	for (i = 0; i < MAX40080_NUM_RANGES; i++) {
+		tmp = (u64)MAX40080_INTER_VREF_MV * NANO * MICRO;
+		tmp = div64_u64(tmp, (u64)MAX40080_ADC_RES * max40080_csa_gain[i] *
+				st->shunt_resistor_uohm);
+		st->current_scale[i][0] = div_u64_rem(tmp, NANO, &rem);
+		st->current_scale[i][1] = rem;
+	}
+}
+
+static int max40080_get_oversampling_ratio(struct max40080_state *st, int *val)
+{
+	*val = st->oversampling_ratio;
+
+	return 0;
+}
+
+/*
+ * max40080_oversampling_avail[] is ordered so that its index is the FILTER
+ * field value (index 0 = no averaging, index 1 = 8x, ...). Return that index
+ * for an exact match, or -EINVAL for a value that is not on the list.
+ */
+static int max40080_oversampling_to_filter(int val)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(max40080_oversampling_avail); i++)
+		if (max40080_oversampling_avail[i] == val)
+			return i;
+
+	return -EINVAL;
+}
+
+static int max40080_set_oversampling_ratio(struct max40080_state *st, int val)
+{
+	int ret, filter = max40080_oversampling_to_filter(val);
+
+	if (filter < 0)
+		return filter;
+
+	ret = max40080_update_bits(st, MAX40080_REG_CFG, MAX40080_FILTER_MSK,
+				   FIELD_PREP(MAX40080_FILTER_MSK, filter));
+	if (ret)
+		return ret;
+
+	st->oversampling_ratio = val;
+
+	return 0;
+}
+
+static int max40080_read_raw(struct iio_dev *indio_dev,
+			     struct iio_chan_spec const *chan,
+			     int *val,
+			     int *val2,
+			     long mask)
+{
+	struct max40080_state *st = iio_priv(indio_dev);
+	int ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		if (chan->type == IIO_CURRENT) {
+			ret = max40080_get_current(st, val);
+			if (ret)
+				return ret;
+		} else if (chan->type == IIO_VOLTAGE) {
+			ret = max40080_get_voltage(st, val);
+			if (ret)
+				return ret;
+		}
+
+		return IIO_VAL_INT;
+	case IIO_CHAN_INFO_SCALE:
+		if (chan->type == IIO_CURRENT) {
+			/*
+			 * The selectable current-sense range is exposed through
+			 * scale: each RANGE setting has its own precomputed
+			 * mA-per-code value. Userspace picks the range by writing
+			 * the matching scale.
+			 */
+			*val = st->current_scale[st->range][0];
+			*val2 = st->current_scale[st->range][1];
+			return IIO_VAL_INT_PLUS_NANO;
+		}
+		/* voltage[mV] = raw * Vref[mV] * buffer_gain / ADC_RES */
+		*val = MAX40080_INTER_VREF_MV * MAX40080_V_BUFF_GAIN;
+		*val2 = MAX40080_ADC_RES;
+		return IIO_VAL_FRACTIONAL;
+	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
+		ret = max40080_get_oversampling_ratio(st, val);
+		if (ret)
+			return ret;
+		return IIO_VAL_INT;
+	default:
+		return -EINVAL;
+	}
+}
+
+static int max40080_write_raw(struct iio_dev *indio_dev,
+			      struct iio_chan_spec const *chan,
+			      int val, int val2, long mask)
+{
+	struct max40080_state *st = iio_priv(indio_dev);
+	unsigned int i;
+	int ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_SCALE:
+		/* Only the current channel has a selectable range/scale. */
+		if (chan->type != IIO_CURRENT)
+			return -EINVAL;
+
+		for (i = 0; i < MAX40080_NUM_RANGES; i++)
+			if (val == st->current_scale[i][0] &&
+			    val2 == st->current_scale[i][1])
+				return max40080_set_range(st, i);
+
+		return -EINVAL;
+	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
+		ret = max40080_set_oversampling_ratio(st, val);
+		if (ret)
+			return ret;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int max40080_write_raw_get_fmt(struct iio_dev *indio_dev,
+				      struct iio_chan_spec const *chan,
+				      long mask)
+{
+	switch (mask) {
+	case IIO_CHAN_INFO_SCALE:
+		return IIO_VAL_INT_PLUS_NANO;
+	default:
+		return IIO_VAL_INT;
+	}
+}
+
+static int max40080_read_avail(struct iio_dev *indio_dev,
+			       struct iio_chan_spec const *chan,
+			       const int **vals, int *type, int *length,
+			       long info)
+{
+	struct max40080_state *st = iio_priv(indio_dev);
+
+	switch (info) {
+	case IIO_CHAN_INFO_SCALE:
+		if (chan->type != IIO_CURRENT)
+			return -EINVAL;
+
+		*vals = (int *)st->current_scale;
+		*length = MAX40080_NUM_RANGES * 2;
+		*type = IIO_VAL_INT_PLUS_NANO;
+		return IIO_AVAIL_LIST;
+	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
+		*vals = max40080_oversampling_avail;
+		*length = ARRAY_SIZE(max40080_oversampling_avail);
+		*type = IIO_VAL_INT;
+		return IIO_AVAIL_LIST;
+	default:
+		return -EINVAL;
+	}
+}
+
+static int max40080_reg_access(struct iio_dev *indio_dev,
+			       unsigned int reg,
+			       unsigned int write_val,
+			       unsigned int *read_val)
+{
+	struct max40080_state *st = iio_priv(indio_dev);
+
+	if (read_val) {
+		int val = i2c_smbus_read_word_data(st->client, reg);
+
+		if (val < 0)
+			return val;
+		*read_val = val;
+		return 0;
+	}
+
+	return i2c_smbus_write_word_data(st->client, reg, write_val);
+}
+
+static const struct iio_info max40080_info = {
+	.read_raw = max40080_read_raw,
+	.write_raw = max40080_write_raw,
+	.write_raw_get_fmt = max40080_write_raw_get_fmt,
+	.read_avail = max40080_read_avail,
+	.debugfs_reg_access = &max40080_reg_access,
+};
+
+static const struct iio_chan_spec max40080_channels[] = {
+	{
+		.type = IIO_CURRENT,
+		.indexed = 1,
+		.channel = 0,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+				      BIT(IIO_CHAN_INFO_SCALE),
+		.info_mask_separate_available = BIT(IIO_CHAN_INFO_SCALE),
+		.info_mask_shared_by_all = BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
+		.info_mask_shared_by_all_available =
+			BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
+	},
+	{
+		.type = IIO_VOLTAGE,
+		.indexed = 1,
+		.channel = 0,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+				      BIT(IIO_CHAN_INFO_SCALE),
+		.info_mask_shared_by_all = BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
+		.info_mask_shared_by_all_available =
+			BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
+	},
+};
+
+/*
+ * Configure the device from the cached state. The device powers up in standby
+ * with PEC enabled (CFG POR = 0x0060), so PEC is kept enabled throughout.
+ */
+static int max40080_init(struct max40080_state *st)
+{
+	u16 fifo_cfg, cfg;
+	int ret, filter;
+
+	filter = max40080_oversampling_to_filter(st->oversampling_ratio);
+	if (filter < 0)
+		return filter;
+
+	/*
+	 * Put the device in standby before (re)configuring the FIFO: the FIFO
+	 * configuration register can only be written while the device is not
+	 * converting.
+	 */
+	cfg = FIELD_PREP(MAX40080_MODE_MSK, MAX40080_STDBY_MODE) |
+	      FIELD_PREP(MAX40080_PEC_EN_MSK, 1);
+	ret = i2c_smbus_write_word_data(st->client, MAX40080_REG_CFG, cfg);
+	if (ret)
+		return ret;
+
+	/* Store a matched current+voltage pair per conversion. */
+	fifo_cfg = FIELD_PREP(MAX40080_STORE_IV_MSK, MAX40080_STORE_I_V);
+	ret = i2c_smbus_write_word_data(st->client, MAX40080_REG_FIFO_CFG,
+					fifo_cfg);
+	if (ret)
+		return ret;
+
+	/*
+	 * Use single-measurement mode: the device stays idle and converts once
+	 * per SMBus Quick Command (see max40080_trigger_measurement()), so each
+	 * read returns a fresh sample rather than a queued FIFO entry.
+	 */
+	cfg = FIELD_PREP(MAX40080_MODE_MSK, MAX40080_SINGLE_MODE) |
+	      FIELD_PREP(MAX40080_PEC_EN_MSK, 1) |
+	      FIELD_PREP(MAX40080_RANGE_MSK, st->range) |
+	      FIELD_PREP(MAX40080_FILTER_MSK, filter);
+
+	ret = i2c_smbus_write_word_data(st->client, MAX40080_REG_CFG, cfg);
+	if (ret)
+		return ret;
+
+	return 0;
+}
+
+static int max40080_probe(struct i2c_client *client)
+{
+	const char *propname = "shunt-resistor-micro-ohms";
+	struct device *dev = &client->dev;
+	struct iio_dev *indio_dev;
+	struct max40080_state *st;
+	int ret;
+
+	/*
+	 * The device powers up with PEC enabled (CFG POR = 0x0060) and rejects
+	 * unprotected transactions, so PEC support is mandatory, along with word
+	 * access, the I2C block read used for the current/voltage pair, and the
+	 * Quick Command used to trigger a conversion.
+	 */
+	if (!i2c_check_functionality(client->adapter,
+				     I2C_FUNC_SMBUS_WORD_DATA |
+				     I2C_FUNC_SMBUS_I2C_BLOCK |
+				     I2C_FUNC_SMBUS_QUICK |
+				     I2C_FUNC_SMBUS_PEC))
+		return -EOPNOTSUPP;
+
+	client->flags |= I2C_CLIENT_PEC;
+
+	indio_dev = devm_iio_device_alloc(dev, sizeof(*st));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	i2c_set_clientdata(client, indio_dev);
+
+	st = iio_priv(indio_dev);
+	st->client = client;
+
+	ret = devm_mutex_init(dev, &st->lock);
+	if (ret)
+		return ret;
+
+	ret = device_property_read_u32(dev, propname, &st->shunt_resistor_uohm);
+	if (ret)
+		return dev_err_probe(dev, ret, "can't read %s\n", propname);
+	if (!st->shunt_resistor_uohm)
+		return dev_err_probe(dev, -EINVAL, "%s must be non-zero\n",
+				     propname);
+
+	max40080_calc_current_scale(st);
+
+	/* Defaults: 50 mV range (index 0), no averaging. */
+	st->range = 0;
+	st->oversampling_ratio = 1;
+
+	indio_dev->name = "max40080";
+	indio_dev->info = &max40080_info;
+	indio_dev->modes = INDIO_DIRECT_MODE;
+	indio_dev->channels = max40080_channels;
+	indio_dev->num_channels = ARRAY_SIZE(max40080_channels);
+
+	ret = max40080_init(st);
+	if (ret)
+		return ret;
+
+	return devm_iio_device_register(dev, indio_dev);
+}
+
+static const struct i2c_device_id max40080_i2c_ids[] = {
+	{ "max40080" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, max40080_i2c_ids);
+
+static const struct of_device_id max40080_of_match[] = {
+	{ .compatible = "maxim,max40080" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, max40080_of_match);
+
+static struct i2c_driver max40080_driver = {
+	.driver = {
+		.name = "max40080",
+		.of_match_table = max40080_of_match,
+	},
+	.probe = max40080_probe,
+	.id_table = max40080_i2c_ids,
+};
+module_i2c_driver(max40080_driver);
+
+MODULE_AUTHOR("Ciprian Hegbeli <ciprian.hegbeli@analog.com>");
+MODULE_AUTHOR("Stefan Popa <stefan.popa@analog.com>");
+MODULE_DESCRIPTION("Analog Devices MAX40080 current-sense amplifier driver");
+MODULE_LICENSE("GPL");
-- 
2.53.0

Re: [PATCH v5 1/2] dt-bindings: iio: adc: add maxim,max40080

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] Incomplete DT binding schema due to missing standard hardware properties
--

--- Patch [1]: [PATCH v5 1/2] dt-bindings: iio: adc: add maxim,max40080 ---
commit 613bf10ba7af5c378c448dbcf5f6af9c11712984
Author: Stefan Popa <stefan.popa@analog.com>

dt-bindings: iio: adc: add maxim,max40080

This commit adds device tree bindings for the Maxim MAX40080 bidirectional
current-sense amplifier. It defines standard properties and parameters like
the shunt resistor value used for scaling the reported current.

> diff --git a/Documentation/devicetree/bindings/iio/adc/maxim,max40080.yaml b/Documentation/devicetree/bindings/iio/adc/maxim,max40080.yaml
> new file mode 100644
> index 0000000000000..170bf4eff8706
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/adc/maxim,max40080.yaml
[ ... ]
> +properties:
> +  compatible:
> +    const: maxim,max40080
> +
> +  reg:
> +    maxItems: 1
> +
> +  "#io-channel-cells":
> +    const: 1
> +
> +  shunt-resistor-micro-ohms:
> +    description:
> +      Value of the current-sense shunt resistor connected between the IN+ and
> +      IN- inputs. Used to scale the reported current.
> +
> +required:
> +  - compatible
> +  - reg
> +  - shunt-resistor-micro-ohms
> +
> +additionalProperties: false

[Severity: Low]
The commit message mentions an internal FIFO, which usually implies an
interrupt pin is available to signal data ready or alerts. Physical devices
also typically have power supply requirements, such as a vdd-supply.

Since additionalProperties is set to false, will device trees that accurately
describe these physical hardware connections fail schema validation? Should
definitions for interrupts or power supplies be added to the properties block
to bypass the additionalProperties restriction?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260723065036.2683075-1-stefan.popa@analog.com?part=1

Re: [PATCH v5 2/2] iio: adc: add MAX40080 current-sense amplifier driver

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [Medium] Software state can desynchronize from hardware configuration due to TOCTOU race during concurrent sysfs writes.
- [Low] The i2c_device_id array is missing required named initializers.
--

--- Patch [2]: [PATCH v5 2/2] iio: adc: add MAX40080 current-sense amplifier driver ---
commit 0c56883df0b122ded44daf6d01973fa32a6c55e4
Author: Stefan Popa <stefan.popa@analog.com>

iio: adc: add MAX40080 current-sense amplifier driver
    
This commit adds a direct-mode IIO driver for the MAX40080 bidirectional
current-sense amplifier. It exposes current and voltage channels over an
I2C/SMBus interface.

> diff --git a/drivers/iio/adc/max40080.c b/drivers/iio/adc/max40080.c
> new file mode 100644
> index 0000000000000..cdf626dccb24f
> --- /dev/null
> +++ b/drivers/iio/adc/max40080.c

[ ... ]

> +static int max40080_set_range(struct max40080_state *st, unsigned int range)
> +{
> +	int ret;
> +
> +	ret = max40080_update_bits(st, MAX40080_REG_CFG, MAX40080_RANGE_MSK,
> +				   FIELD_PREP(MAX40080_RANGE_MSK, range));
> +	if (ret)
> +		return ret;
> +
> +	st->range = range;
> +
> +	return 0;
> +}

[Severity: Medium]
Since max40080_update_bits() acquires and releases the mutex internally, 
does this leave the assignment of st->range unprotected against concurrent
sysfs writes? 

If two threads write to the sysfs attribute at the same time, could the 
cached software state become permanently desynchronized from the actual 
hardware configuration, causing future readings to be scaled incorrectly?

[ ... ]

> +static int max40080_set_oversampling_ratio(struct max40080_state *st, int val)
> +{
> +	int ret, filter = max40080_oversampling_to_filter(val);
> +
> +	if (filter < 0)
> +		return filter;
> +
> +	ret = max40080_update_bits(st, MAX40080_REG_CFG, MAX40080_FILTER_MSK,
> +				   FIELD_PREP(MAX40080_FILTER_MSK, filter));
> +	if (ret)
> +		return ret;
> +
> +	st->oversampling_ratio = val;
> +
> +	return 0;
> +}

[Severity: Medium]
Similarly to max40080_set_range(), is the update of st->oversampling_ratio
vulnerable to a race condition since it happens after max40080_update_bits()
has released the lock?

[ ... ]

> +static const struct i2c_device_id max40080_i2c_ids[] = {
> +	{ "max40080" },
> +	{ }
> +};

[Severity: Low]
Does this violate the I2C subsystem coding style guidelines which mandate
named initializers for initialized arrays of type struct i2c_device_id? 

Should this be .name = "max40080" to prevent issues if the struct definition 
changes in the future?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260723065036.2683075-1-stefan.popa@analog.com?part=2