[PATCH v6 0/2] iio: adc: add MAX40080 current-sense amplifier driver

[PATCH v6 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 v5:
  - Add register prefixes (MAX40080_CFG_MODE_MSK, etc.) for clarity
    (Jonathan).
  - Define MAX40080_CFG_RANGE_50MV/10MV with designated initializers
    (Jonathan, Guenter).
  - Use MAX40080_ADC_RES_BITS (12) instead of 4096 (Jonathan).
  - Use IIO_VAL_FRACTIONAL_LOG2 for voltage scale (Jonathan).
  - Return i2c_smbus_write_word_data() directly at end of max40080_init()
    (Jonathan).
  - Hold lock in write_raw for proper cache protection; local range copy
    in read_raw prevents torn reads (Jonathan, Nuno, Sashiko).
  - Add comment explaining intentional *iv = tmp before error check
    (Siratul).
  - Blank line consistency fixes in read_raw switch cases and
    max40080_init() (Siratul).
  - Use adi,max40080 compatible prefix (David).
  - Add vdd-supply and interrupts properties to binding (David).

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/20260723065036.2683075-1-stefan.popa@analog.com/ [v5]
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 adi,max40080
  iio: adc: add MAX40080 current-sense amplifier driver

 .../bindings/iio/adc/adi,max40080.yaml        |  63 ++
 MAINTAINERS                                   |   9 +
 drivers/iio/adc/Kconfig                       |  11 +
 drivers/iio/adc/Makefile                      |   1 +
 drivers/iio/adc/max40080.c                    | 574 ++++++++++++++++++
 5 files changed, 658 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/adc/adi,max40080.yaml
 create mode 100644 drivers/iio/adc/max40080.c

--
2.53.0

[PATCH v6 1/2] dt-bindings: iio: adc: add adi,max40080

[Stefan Popa]

Add device tree bindings for the Analog Devices 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/adi,max40080.yaml        | 63 +++++++++++++++++++
 MAINTAINERS                                   |  8 +++
 2 files changed, 71 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/adc/adi,max40080.yaml

diff --git a/Documentation/devicetree/bindings/iio/adc/adi,max40080.yaml b/Documentation/devicetree/bindings/iio/adc/adi,max40080.yaml
new file mode 100644
index 0000000000000..8dddf58e44125
--- /dev/null
+++ b/Documentation/devicetree/bindings/iio/adc/adi,max40080.yaml
@@ -0,0 +1,63 @@
+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/adc/adi,max40080.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Analog Devices 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: adi,max40080
+
+  reg:
+    maxItems: 1
+
+  "#io-channel-cells":
+    const: 1
+
+  vdd-supply:
+    description: Power supply for the device.
+
+  interrupts:
+    maxItems: 1
+    description: ALERT output for overcurrent/undervoltage threshold events.
+
+  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 = "adi,max40080";
+            reg = <0x20>;
+            #io-channel-cells = <1>;
+            shunt-resistor-micro-ohms = <100000>;
+        };
+    };
diff --git a/MAINTAINERS b/MAINTAINERS
index e087673237636..e1170230c4bb2 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -28893,3 +28893,11 @@ S:	Buried alive in reporters
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
 F:	*
 F:	*/
+
+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/adi,max40080.yaml
-- 
2.53.0

Re: [PATCH v6 1/2] dt-bindings: iio: adc: add adi,max40080

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] The MAINTAINERS entry for 'MAXIM MAX40080 CURRENT SENSE AMPLIFIER DRIVER' is incorrectly appended to the very end of the file, placing it after the catch-all 'THE REST' section.
--

--- Patch [1]: [PATCH v6 1/2] dt-bindings: iio: adc: add adi,max40080 ---
commit 4f01f75006cab658c6276517a4096c41a91e9b17
Author: Stefan Popa <stefan.popa@analog.com>

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

This commit adds device tree bindings for the Analog Devices MAX40080
bidirectional current-sense amplifier. It outlines the required properties
and creates a new maintainer entry for the driver.

> diff --git a/MAINTAINERS b/MAINTAINERS
> --- a/MAINTAINERS
> +++ b/MAINTAINERS

[ ... ]

> @@ -27447,3 +27447,11 @@ S:	Buried alive in reporters
>  T:	git git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
>  F:	*
>  F:	*/
> +
> +MAXIM MAX40080 CURRENT SENSE AMPLIFIER DRIVER

[Severity: Low]
This isn't a bug, but should this new entry be sorted alphabetically within
the file? Appending it at the very bottom places it after the catch-all
fallback section, which violates the standard sorting convention.

> +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/adi,max40080.yaml

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260730131738.822405-1-stefan.popa@analog.com?part=1

Re: [PATCH v6 1/2] dt-bindings: iio: adc: add adi,max40080

[Siratul Islam]

July 30, 2026 at 7:17 PM, "Stefan Popa" <stefan.popa@analog.com> wrote:


> 
> Add device tree bindings for the Analog Devices MAX40080 bidirectional
> current-sense amplifier with a 12-bit ADC and an I2C/SMBus interface.
> 
> Signed-off-by: Stefan Popa <stefan.popa@analog.com>
> ---
...
> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/iio/adc/adi,max40080.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Analog Devices 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
About this link, there were some discussion in the previous version where
Jonathan suggested a more standard format (https://www.analog.com/max40080).
But you seem to have kept the same url as before. I'll leave it up to him. 
> +
> +properties:
> + compatible:
> + const: adi,max40080
> +
...
> +
> +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/adi,max40080.yaml
> -- 
> 2.53.0
>
Please maintain alphabetical order for the MAINTAINERS entry, 
instead of adding it to the end of the file.

Re: [PATCH v6 1/2] dt-bindings: iio: adc: add adi,max40080

[Krzysztof Kozlowski]

On Thu, Jul 30, 2026 at 04:17:37PM +0300, Stefan Popa wrote:
> +  vdd-supply:
> +    description: Power supply for the device.
> +
> +  interrupts:
> +    maxItems: 1
> +    description: ALERT output for overcurrent/undervoltage threshold events.
> +
> +  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

Supply is required

> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    i2c {
> +        #address-cells = <1>;
> +        #size-cells = <0>;
> +
> +        adc@20 {
> +            compatible = "adi,max40080";
> +            reg = <0x20>;
> +            #io-channel-cells = <1>;
> +            shunt-resistor-micro-ohms = <100000>;
> +        };
> +    };
> diff --git a/MAINTAINERS b/MAINTAINERS
> index e087673237636..e1170230c4bb2 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -28893,3 +28893,11 @@ S:	Buried alive in reporters
>  T:	git git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
>  F:	*
>  F:	*/
> +
> +MAXIM MAX40080 CURRENT SENSE AMPLIFIER DRIVER

Honestly, how did it appear at the end? Do you see any other
commit/patchset adding it there? No, so this should raise questions on
your side.

Best regards,
Krzysztof

Re: [PATCH v6 1/2] dt-bindings: iio: adc: add adi,max40080

[Krzysztof Kozlowski]

On 31/07/2026 09:04, Krzysztof Kozlowski wrote:
> On Thu, Jul 30, 2026 at 04:17:37PM +0300, Stefan Popa wrote:
>> +  vdd-supply:
>> +    description: Power supply for the device.
>> +
>> +  interrupts:
>> +    maxItems: 1
>> +    description: ALERT output for overcurrent/undervoltage threshold events.
>> +
>> +  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
> 
> Supply is required
> 
>> +
>> +additionalProperties: false
>> +
>> +examples:
>> +  - |
>> +    i2c {
>> +        #address-cells = <1>;
>> +        #size-cells = <0>;
>> +
>> +        adc@20 {
>> +            compatible = "adi,max40080";
>> +            reg = <0x20>;
>> +            #io-channel-cells = <1>;
>> +            shunt-resistor-micro-ohms = <100000>;
>> +        };
>> +    };
>> diff --git a/MAINTAINERS b/MAINTAINERS
>> index e087673237636..e1170230c4bb2 100644
>> --- a/MAINTAINERS
>> +++ b/MAINTAINERS
>> @@ -28893,3 +28893,11 @@ S:	Buried alive in reporters
>>  T:	git git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
>>  F:	*
>>  F:	*/
>> +
>> +MAXIM MAX40080 CURRENT SENSE AMPLIFIER DRIVER
> 
> Honestly, how did it appear at the end? Do you see any other
> commit/patchset adding it there? No, so this should raise questions on
> your side.

And this is quite different than v5 and nothing explains that change in
the changelog.

Use b4 prep to see what you did between revisions.

Best regards,
Krzysztof

[PATCH v6 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.

The driver operates in single-measurement mode: each raw read triggers
an on-demand conversion via SMBus Quick Command and returns a matched
current/voltage pair. This avoids the latency and complexity of the
continuous FIFO mode while ensuring each read reflects the current
state. The two selectable current-sense ranges are exposed through
scale/scale_available.

Continuous FIFO buffering, threshold events and the alert interrupt are
intentionally left out of this initial submission and may be added
later.

Co-developed-by: Ciprian Hegbeli <ciprian.hegbeli@analog.com>
Signed-off-by: Ciprian Hegbeli <ciprian.hegbeli@analog.com>
Signed-off-by: Stefan Popa <stefan.popa@analog.com>
---
 MAINTAINERS                |   1 +
 drivers/iio/adc/Kconfig    |  11 +
 drivers/iio/adc/Makefile   |   1 +
 drivers/iio/adc/max40080.c | 574 +++++++++++++++++++++++++++++++++++++
 4 files changed, 587 insertions(+)
 create mode 100644 drivers/iio/adc/max40080.c

diff --git a/MAINTAINERS b/MAINTAINERS
index e1170230c4bb2..467e6bbf72cde 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -28901,3 +28901,4 @@ L:	linux-iio@vger.kernel.org
 S:	Supported
 W:	https://ez.analog.com/linux-software-drivers
 F:	Documentation/devicetree/bindings/iio/adc/adi,max40080.yaml
+F:	drivers/iio/adc/max40080.c
diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
index 58da8255525e4..ebdbad81fbbd6 100644
--- a/drivers/iio/adc/Kconfig
+++ b/drivers/iio/adc/Kconfig
@@ -1907,3 +1907,14 @@ config XILINX_AMS
 	  xilinx-ams.
 
 endmenu
+
+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.
diff --git a/drivers/iio/adc/Makefile b/drivers/iio/adc/Makefile
index 7cc8f9a12f763..9245a337dd935 100644
--- a/drivers/iio/adc/Makefile
+++ b/drivers/iio/adc/Makefile
@@ -166,3 +166,4 @@ obj-$(CONFIG_VIPERBOARD_ADC) += viperboard_adc.o
 obj-$(CONFIG_XILINX_AMS) += xilinx-ams.o
 xilinx-xadc-y := xilinx-xadc-core.o xilinx-xadc-events.o
 obj-$(CONFIG_XILINX_XADC) += xilinx-xadc.o
+obj-$(CONFIG_MAX40080) += max40080.o
diff --git a/drivers/iio/adc/max40080.c b/drivers/iio/adc/max40080.c
new file mode 100644
index 0000000000000..82572536b704d
--- /dev/null
+++ b/drivers/iio/adc/max40080.c
@@ -0,0 +1,574 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * MAX40080 Digital Current-Sense Amplifier driver
+ *
+ * Copyright 2026 Analog Devices, Inc.
+ *
+ * Datasheet: https://www.analog.com/media/en/technical-documentation/data-sheets/MAX40080.pdf
+ */
+
+#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_CFG_MODE_MSK		GENMASK(2, 0)
+#define  MAX40080_CFG_PEC_EN_MSK	BIT(5)
+#define  MAX40080_CFG_RANGE_MSK		BIT(6)
+#define  MAX40080_CFG_FILTER_MSK	GENMASK(14, 12)
+
+#define MAX40080_REG_FIFO_CFG		0x0A
+#define  MAX40080_FIFO_CFG_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 values. */
+#define MAX40080_CFG_MODE_STDBY		0x00
+#define MAX40080_CFG_MODE_SINGLE	0x02
+
+/* CFG.range field values. */
+#define MAX40080_CFG_RANGE_50MV		0
+#define MAX40080_CFG_RANGE_10MV		1
+
+/* FIFO_CFG.store_iv field values. */
+#define MAX40080_FIFO_CFG_STORE_I_V	0x02
+
+#define MAX40080_ADC_RES_BITS		12
+#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). Indexed
+ * by the CFG.range field value.
+ */
+static const int max40080_csa_gain[] = {
+	[MAX40080_CFG_RANGE_50MV] = MAX40080_CSA_50MV_GAIN,
+	[MAX40080_CFG_RANGE_10MV] = 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 tmp;
+
+	tmp = i2c_smbus_read_word_data(st->client, reg);
+	if (tmp < 0)
+		return tmp;
+
+	tmp = (tmp & ~mask) | (val & mask);
+
+	return i2c_smbus_write_word_data(st->client, reg, tmp);
+}
+
+/*
+ * 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);
+	/*
+	 * Propagate the last-read value even on timeout so the caller can
+	 * inspect it for debugging.
+	 */
+	*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_CFG_RANGE_MSK,
+				   FIELD_PREP(MAX40080_CFG_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] / ((1 << ADC_RES_BITS) * gain)
+ * and current = Vshunt / Rshunt, so with Rshunt in micro-ohms the scale in
+ * mA/code is
+ *   Vref[mV] * NANO * MICRO / ((1 << ADC_RES_BITS) * gain * Rshunt[uohm])
+ * expressed as an integer part plus a nano fractional part.
+ */
+static void max40080_calc_current_scale(struct max40080_state *st)
+{
+	u32 rem;
+	u64 tmp;
+
+	for (unsigned int i = 0; i < MAX40080_NUM_RANGES; i++) {
+		tmp = (u64)MAX40080_INTER_VREF_MV * NANO * MICRO;
+		tmp = div64_u64(tmp, (u64)(1 << MAX40080_ADC_RES_BITS) * 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;
+	}
+}
+
+/*
+ * 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)
+{
+	for (unsigned int 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 filter;
+	int ret;
+
+	filter = max40080_oversampling_to_filter(val);
+	if (filter < 0)
+		return filter;
+
+	ret = max40080_update_bits(st, MAX40080_REG_CFG, MAX40080_CFG_FILTER_MSK,
+				   FIELD_PREP(MAX40080_CFG_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);
+	unsigned int range;
+	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.
+			 *
+			 * Take a local copy of range to ensure val and val2 come
+			 * from the same setting even if a concurrent write changes
+			 * st->range between the two accesses.
+			 */
+			range = st->range;
+			*val = st->current_scale[range][0];
+			*val2 = st->current_scale[range][1];
+			return IIO_VAL_INT_PLUS_NANO;
+		}
+		/* voltage[mV] = raw * Vref[mV] * buffer_gain / (1 << ADC_RES_BITS) */
+		*val = MAX40080_INTER_VREF_MV * MAX40080_V_BUFF_GAIN;
+		*val2 = MAX40080_ADC_RES_BITS;
+		return IIO_VAL_FRACTIONAL_LOG2;
+	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
+		*val = st->oversampling_ratio;
+		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);
+
+	guard(mutex)(&st->lock);
+
+	switch (mask) {
+	case IIO_CHAN_INFO_SCALE:
+		/* Only the current channel has a selectable range/scale. */
+		if (chan->type != IIO_CURRENT)
+			return -EINVAL;
+
+		for (unsigned int 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:
+		return max40080_set_oversampling_ratio(st, val);
+	default:
+		return -EINVAL;
+	}
+}
+
+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);
+	int val;
+
+	if (read_val) {
+		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_CFG_MODE_MSK, MAX40080_CFG_MODE_STDBY) |
+	      FIELD_PREP(MAX40080_CFG_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_FIFO_CFG_STORE_IV_MSK, MAX40080_FIFO_CFG_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_CFG_MODE_MSK, MAX40080_CFG_MODE_SINGLE) |
+	      FIELD_PREP(MAX40080_CFG_PEC_EN_MSK, 1) |
+	      FIELD_PREP(MAX40080_CFG_RANGE_MSK, st->range) |
+	      FIELD_PREP(MAX40080_CFG_FILTER_MSK, filter);
+
+	return i2c_smbus_write_word_data(st->client, MAX40080_REG_CFG, cfg);
+}
+
+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;
+
+	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, no averaging. */
+	st->range = MAX40080_CFG_RANGE_50MV;
+	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[] = {
+	{ .name = "max40080" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, max40080_i2c_ids);
+
+static const struct of_device_id max40080_of_match[] = {
+	{ .compatible = "adi,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 v6 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:
- [High] Stale measurements: each raw sysfs read returns the previous conversion's data due to an un-flushed FIFO.
- [Medium] Missing READ_ONCE() for `st->range` in `max40080_read_raw()` can lead to data races and torn scale values.
--

--- Patch [2]: [PATCH v6 2/2] iio: adc: add MAX40080 current-sense amplifier driver ---
commit 557f2827eeb4edfa93bf2f63edf6a0664453dad6
Author: Stefan Popa <stefan.popa@analog.com>

iio: adc: add MAX40080 current-sense amplifier driver

The patch adds a direct-mode IIO driver for the MAX40080 current-sense
amplifier, exposing current and voltage channels with configurable
oversampling.

> diff --git a/drivers/iio/adc/max40080.c b/drivers/iio/adc/max40080.c
> new file mode 100644
> index 0000000000000..82572536b704d
> --- /dev/null
> +++ b/drivers/iio/adc/max40080.c

[ ... ]

> +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);

[Severity: High]
Does this polling loop read a stale sample?

Writing the SINGLE mode configuration in max40080_init() triggers an initial
conversion, leaving a sample in the FIFO. Because the FIFO already contains
this unread sample, the read_poll_timeout() loop here might instantly succeed
and pop the stale sample before the newly triggered measurement has a chance
to complete.

This would cause each sysfs read to return the previous conversion's data.

> +	/*
> +	 * Propagate the last-read value even on timeout so the caller can
> +	 * inspect it for debugging.
> +	 */
> +	*iv = tmp;
> +	if (ret)
> +		return ret;
> +
> +	return io_ret;
> +}

[ ... ]

> +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);
> +	unsigned int range;
> +	int ret;
> +
> +	switch (mask) {

[ ... ]

> +	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.
> +			 *
> +			 * Take a local copy of range to ensure val and val2 come
> +			 * from the same setting even if a concurrent write changes
> +			 * st->range between the two accesses.
> +			 */
> +			range = st->range;
> +			*val = st->current_scale[range][0];
> +			*val2 = st->current_scale[range][1];

[Severity: Medium]
Could this result in a torn read if st->range is modified concurrently?

Without a READ_ONCE() for st->range, the compiler might optimize away the local
variable and reload st->range directly from memory between reading
st->current_scale[range][0] and st->current_scale[range][1].

If max40080_write_raw() modifies st->range concurrently, this could return an
invalid combination of integer and fractional components.

> +			return IIO_VAL_INT_PLUS_NANO;
> +		}

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260730131738.822405-1-stefan.popa@analog.com?part=2

Re: [PATCH v6 2/2] iio: adc: add MAX40080 current-sense amplifier driver

[Siratul Islam]

On Thu, 2026-07-30 at 16:17 +0300, Stefan Popa wrote:
> 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.
> 
...
> +
> +#define MAX40080_REG_FIFO_CFG		0x0A
> +#define  MAX40080_FIFO_CFG_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 values. */
> +#define MAX40080_CFG_MODE_STDBY		0x00
> +#define MAX40080_CFG_MODE_SINGLE	0x02
> +
> +/* CFG.range field values. */
> +#define MAX40080_CFG_RANGE_50MV		0
> +#define MAX40080_CFG_RANGE_10MV		1
this and other "MV"s below should be mV(m lowercase) as 
I suggested in the previous version.
> +
> +/* FIFO_CFG.store_iv field values. */
> +#define MAX40080_FIFO_CFG_STORE_I_V	0x02
I also had a question on why this is I_V and not IV like the rest of them?
> +
> +#define MAX40080_ADC_RES_BITS		12
> +#define MAX40080_INTER_VREF_MV		1250
> +#define MAX40080_V_BUFF_GAIN		30
> +#define MAX40080_CSA_50MV_GAIN		25
> +#define MAX40080_CSA_10MV_GAIN		125
...
Looks like you missed some of the reviews. If it was intentional,
please acknowledge that. It is a good idea to reply to emails
and discuss/confirm stuff before sending a new patch.

Also avoid sending --to mailing lists (linux-iio@vger.kernel.org). 
Send to maintainers and Cc reviewers and lists.

--
Best regards,
Sirat