[PATCH v3 0/2] iio: dac: mcp47a1: add support for new device

[PATCH v3 0/2] iio: dac: mcp47a1: add support for new device

[Joshua Crofts]

This patch series adds support for the MCP47A1 DAC.

The Microchip MCP47A1 is a volatile 6-bit Digital-to-Analog converter
which communicates via I2C. It is a low-power, low-cost DAC commonly
used in embedded systems.

Reasons for adding a new driver:
- Existing Microchip DACs use a more complicated set of commands
  whereas the MCP47A1 communicates via SMBus using only one command.
- The closest Microchip DAC already in the tree - the MCP4725 - uses
  an EEPROM while the MCP47A1 is volatile, meaning that altering
  the driver of the former would worsen the code flow.
- The MCP47A1 maps cleanly to a standard regmap.

The driver was tested on a Raspberry Pi 4 using a breakout board with
the MCP47A1.

The datasheet can be viewed here:
https://ww1.microchip.com/downloads/aemDocuments/documents/OTH/ProductDocuments/DataSheets/25154A.pdf

Signed-off-by: Joshua Crofts <joshua.crofts1@gmail.com>
---
Changes in v3:
- remove iio_chan_spec array and define a separate single channel as
  only one is used
- change scale denominator from 63 to 64 as former would produce scaling
  errors
- Link to v2: https://lore.kernel.org/r/20260727-mcp47a1-add-support-v2-0-d4591a2ce69e@gmail.com

Changes in v2:
- dt-bindings: add slave address enum to dt-binding
- dt-bindings: remove unnecessary example
- move driver from regmap to i2c_smbus_* functions to reduce overhead
- remove read test on probe as it's too unstable
- add 20us delay on startup
- style changes
- remove excess mailing list entry from MAINTAINERS
- Link to v1: https://lore.kernel.org/r/20260721-mcp47a1-add-support-v1-0-da045a2567e3@gmail.com

---
Joshua Crofts (2):
      dt-bindings: iio: dac: add support for mcp47a1
      iio: dac: mcp47a1: add support for new device

 .../bindings/iio/dac/microchip,mcp47a1.yaml        |  50 +++++++
 MAINTAINERS                                        |   6 +
 drivers/iio/dac/Kconfig                            |  10 ++
 drivers/iio/dac/Makefile                           |   1 +
 drivers/iio/dac/mcp47a1.c                          | 166 +++++++++++++++++++++
 5 files changed, 233 insertions(+)
---
base-commit: e0484d62e8e1cff75b210938be835ea6221bda59
change-id: 20260711-mcp47a1-add-support-3af1248f13a5

Best regards,
-- 
Kind regards,
Joshua Crofts

[PATCH v3 1/2] dt-bindings: iio: dac: add support for mcp47a1

[Joshua Crofts]

The Microchip MCP47A1 is a 6-bit volatile Digital-to-Analog converter
which communicates via I2C.

Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Joshua Crofts <joshua.crofts1@gmail.com>
---
 .../bindings/iio/dac/microchip,mcp47a1.yaml        | 50 ++++++++++++++++++++++
 MAINTAINERS                                        |  5 +++
 2 files changed, 55 insertions(+)

diff --git a/Documentation/devicetree/bindings/iio/dac/microchip,mcp47a1.yaml b/Documentation/devicetree/bindings/iio/dac/microchip,mcp47a1.yaml
new file mode 100644
index 000000000000..b181fe73dce8
--- /dev/null
+++ b/Documentation/devicetree/bindings/iio/dac/microchip,mcp47a1.yaml
@@ -0,0 +1,50 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+
+$id: http://devicetree.org/schemas/iio/dac/microchip,mcp47a1.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Microchip MCP47A1 DAC
+
+maintainers:
+  - Joshua Crofts <joshua.crofts1@gmail.com>
+
+description: |
+  The Microchip MCP47A1 is a 6-bit single output volatile DAC.
+  This device can have different IDs (0x2e and 0x3e).
+  https://ww1.microchip.com/downloads/aemDocuments/documents/OTH/ProductDocuments/DataSheets/25154A.pdf
+
+properties:
+  compatible:
+    const: microchip,mcp47a1
+
+  reg:
+    items:
+      - enum: [0x2e, 0x3e]
+
+  vref-supply: true
+
+  vdd-supply: true
+
+required:
+  - compatible
+  - reg
+  - vref-supply
+  - vdd-supply
+
+additionalProperties: false
+
+examples:
+  - |
+    i2c {
+          #address-cells = <1>;
+          #size-cells = <0>;
+
+          dac@2e {
+              compatible = "microchip,mcp47a1";
+              reg = <0x2e>;
+              vref-supply = <&vref_regulator>;
+              vdd-supply = <&vdd_regulator>;
+          };
+    };
diff --git a/MAINTAINERS b/MAINTAINERS
index ce020ded5fd3..8c8118eb4141 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -17699,6 +17699,11 @@ S:	Maintained
 F:	Documentation/devicetree/bindings/iio/adc/microchip,mcp3911.yaml
 F:	drivers/iio/adc/mcp3911.c
 
+MICROCHIP MCP47A1 DAC DRIVER
+M:	Joshua Crofts <joshua.crofts1@gmail.com>
+S:	Maintained
+F:	Documentation/devicetree/bindings/iio/dac/microchip,mcp47a1.yaml
+
 MICROCHIP MCP9982 TEMPERATURE DRIVER
 M:	Victor Duicu <victor.duicu@microchip.com>
 L:	linux-hwmon@vger.kernel.org

-- 
2.55.0

Re: [PATCH v3 1/2] dt-bindings: iio: dac: add support for mcp47a1

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [Medium] The I2C addresses specified in the schema and example appear to be 8-bit write addresses instead of the 7-bit addresses required by the DT specification.
- [Low] The `reg` property schema applies an integer `enum` directly to a matrix array element, which will cause `dt_binding_check` validation to always fail.
--

--- Patch [1]: [PATCH v3 1/2] dt-bindings: iio: dac: add support for mcp47a1 ---
commit 441e840b5a2a3f037c3520c49013a55b7dc4c1bd
Author: Joshua Crofts <joshua.crofts1@gmail.com>

dt-bindings: iio: dac: add support for mcp47a1

The Microchip MCP47A1 is a 6-bit volatile Digital-to-Analog converter
which communicates via I2C.

> diff --git a/Documentation/devicetree/bindings/iio/dac/microchip,mcp47a1.yaml b/Documentation/devicetree/bindings/iio/dac/microchip,mcp47a1.yaml
> new file mode 100644
> index 0000000000000..b181fe73dce84
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/dac/microchip,mcp47a1.yaml
[ ... ]
> +properties:
> +  compatible:
> +    const: microchip,mcp47a1
> +
> +  reg:
> +    items:
> +      - enum: [0x2e, 0x3e]

[Severity: Low]
Will this cause dt_binding_check validation to fail?

Since dt-schema parses reg values into a uint32-matrix (an array of arrays),
the items array applied to it defines a tuple schema for the outer array's
elements. This means the inner array [0x2e] will be matched against the
integer enum [0x2e, 0x3e], which will mathematically fail since an array
is not an integer.

[Severity: Medium]
Are these 8-bit write addresses instead of the 7-bit addresses required by
the Device Tree specification?

If these are indeed 8-bit addresses (as indicated by the 0 LSB and typical
Microchip datasheet conventions), they must be shifted right by 1. That would
make the correct 7-bit DT addresses 0x17 and 0x1f.

> +
> +  vref-supply: true
[ ... ]
> +examples:
> +  - |
> +    i2c {
> +          #address-cells = <1>;
> +          #size-cells = <0>;
> +
> +          dac@2e {
> +              compatible = "microchip,mcp47a1";
> +              reg = <0x2e>;

[Severity: Medium]
Does this example propagate the DT specification violation?

Using an 8-bit write address directly in the reg property and unit name
(dac@2e) will cause the device to fail to probe or communicate, as the I2C
subsystem expects a 7-bit address.

> +              vref-supply = <&vref_regulator>;
> +              vdd-supply = <&vdd_regulator>;
> +          };
> +    };

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260803-mcp47a1-add-support-v3-0-540e71b4fd2e@gmail.com?part=1

Re: [PATCH v3 1/2] dt-bindings: iio: dac: add support for mcp47a1

[Joshua Crofts]

On Mon, 03 Aug 2026 18:07:16 +0000
sashiko-bot@kernel.org wrote:

> Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
> - [Medium] The I2C addresses specified in the schema and example appear to be 8-bit write addresses instead of the 7-bit addresses required by the DT specification.
> - [Low] The `reg` property schema applies an integer `enum` directly to a matrix array element, which will cause `dt_binding_check` validation to always fail.
> --
> 
> --- Patch [1]: [PATCH v3 1/2] dt-bindings: iio: dac: add support for mcp47a1 ---
> commit 441e840b5a2a3f037c3520c49013a55b7dc4c1bd
> Author: Joshua Crofts <joshua.crofts1@gmail.com>
> 
> dt-bindings: iio: dac: add support for mcp47a1
> 
> The Microchip MCP47A1 is a 6-bit volatile Digital-to-Analog converter
> which communicates via I2C.
> 
> > diff --git a/Documentation/devicetree/bindings/iio/dac/microchip,mcp47a1.yaml b/Documentation/devicetree/bindings/iio/dac/microchip,mcp47a1.yaml
> > new file mode 100644
> > index 0000000000000..b181fe73dce84
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/iio/dac/microchip,mcp47a1.yaml  
> [ ... ]
> > +properties:
> > +  compatible:
> > +    const: microchip,mcp47a1
> > +
> > +  reg:
> > +    items:
> > +      - enum: [0x2e, 0x3e]  
> 
> [Severity: Low]
> Will this cause dt_binding_check validation to fail?

No, this is a perfectly valid dt-schema which passes dt_binding_check.

> 
> Since dt-schema parses reg values into a uint32-matrix (an array of arrays),
> the items array applied to it defines a tuple schema for the outer array's
> elements. This means the inner array [0x2e] will be matched against the
> integer enum [0x2e, 0x3e], which will mathematically fail since an array
> is not an integer.
> 
> [Severity: Medium]
> Are these 8-bit write addresses instead of the 7-bit addresses required by
> the Device Tree specification?
> 
> If these are indeed 8-bit addresses (as indicated by the 0 LSB and typical
> Microchip datasheet conventions), they must be shifted right by 1. That would
> make the correct 7-bit DT addresses 0x17 and 0x1f.

No clue what Sashiko is on about since these are indeed 7-bit addresses which
do work when tested on the actual hardware.

-- 
Kind regards,
Joshua Crofts

[PATCH v3 2/2] iio: dac: mcp47a1: add support for new device

[Joshua Crofts]

The Microchip MCP47A1 is a 6-bit volatile Digital-to-Analog converter
which communicates via I2C.

Signed-off-by: Joshua Crofts <joshua.crofts1@gmail.com>
---
 MAINTAINERS               |   1 +
 drivers/iio/dac/Kconfig   |  10 +++
 drivers/iio/dac/Makefile  |   1 +
 drivers/iio/dac/mcp47a1.c | 166 ++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 178 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 8c8118eb4141..fc76a2159e1f 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -17703,6 +17703,7 @@ MICROCHIP MCP47A1 DAC DRIVER
 M:	Joshua Crofts <joshua.crofts1@gmail.com>
 S:	Maintained
 F:	Documentation/devicetree/bindings/iio/dac/microchip,mcp47a1.yaml
+F:	drivers/iio/dac/mcp47a1.c
 
 MICROCHIP MCP9982 TEMPERATURE DRIVER
 M:	Victor Duicu <victor.duicu@microchip.com>
diff --git a/drivers/iio/dac/Kconfig b/drivers/iio/dac/Kconfig
index 18a27785e28b..04c90d98f86f 100644
--- a/drivers/iio/dac/Kconfig
+++ b/drivers/iio/dac/Kconfig
@@ -582,6 +582,16 @@ config MCP4728
 	  To compile this driver as a module, choose M here: the module
 	  will be called mcp4728.
 
+config MCP47A1
+	tristate "MCP47A1 DAC driver"
+	depends on I2C
+	help
+	  Say Y here if you want to build a driver for the Microchip
+	  MCP47A1 digital-to-analog converter with an I2C interface.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called mcp47a1.
+
 config MCP47FEB02
 	tristate "MCP47F(E/V)B01/02/04/08/11/12/14/18/21/22/24/28 DAC driver"
 	depends on I2C
diff --git a/drivers/iio/dac/Makefile b/drivers/iio/dac/Makefile
index 5d20d37e44ce..992f8930f95c 100644
--- a/drivers/iio/dac/Makefile
+++ b/drivers/iio/dac/Makefile
@@ -55,6 +55,7 @@ obj-$(CONFIG_MAX5821) += max5821.o
 obj-$(CONFIG_MCF54415_DAC) += mcf54415_dac.o
 obj-$(CONFIG_MCP4725) += mcp4725.o
 obj-$(CONFIG_MCP4728) += mcp4728.o
+obj-$(CONFIG_MCP47A1) += mcp47a1.o
 obj-$(CONFIG_MCP47FEB02) += mcp47feb02.o
 obj-$(CONFIG_MCP4821) += mcp4821.o
 obj-$(CONFIG_MCP4922) += mcp4922.o
diff --git a/drivers/iio/dac/mcp47a1.c b/drivers/iio/dac/mcp47a1.c
new file mode 100644
index 000000000000..0bf994aa0e4f
--- /dev/null
+++ b/drivers/iio/dac/mcp47a1.c
@@ -0,0 +1,166 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Microchip MCP47A1 DAC driver
+ *
+ * Copyright (c) 2026 Joshua Crofts <joshua.crofts1@gmail.com>
+ *
+ * Datasheet: https://ww1.microchip.com/downloads/aemDocuments/documents/OTH/ProductDocuments/DataSheets/25154A.pdf
+ */
+
+#include <linux/delay.h>
+#include <linux/err.h>
+#include <linux/i2c.h>
+#include <linux/minmax.h>
+#include <linux/module.h>
+#include <linux/regulator/consumer.h>
+#include <linux/types.h>
+#include <linux/units.h>
+
+#include <linux/iio/iio.h>
+
+#define MCP47A1_CMD_CODE	0x00
+#define MCP47A1_MAX_STEPS	64
+
+struct mcp47a1_data {
+	struct i2c_client *client;
+	int vref_mV;
+};
+
+static const int mcp47a1_raw_avail[] = { 0, 1, MCP47A1_MAX_STEPS - 1 };
+
+static const struct iio_chan_spec mcp47a1_channel = {
+	.type = IIO_VOLTAGE,
+	.indexed = 1,
+	.output = 1,
+	.channel = 0,
+	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
+	.info_mask_separate_available = BIT(IIO_CHAN_INFO_RAW),
+	.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),
+};
+
+static int mcp47a1_write(struct iio_dev *indio_dev,
+			 struct iio_chan_spec const *chan,
+			 int val, int val2, long mask)
+{
+	struct mcp47a1_data *data = iio_priv(indio_dev);
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		if (!in_range(val, 0, MCP47A1_MAX_STEPS))
+			return -EINVAL;
+
+		return i2c_smbus_write_byte_data(data->client, MCP47A1_CMD_CODE,
+						 val);
+	default:
+		return -EINVAL;
+	}
+}
+
+static int mcp47a1_read(struct iio_dev *indio_dev,
+			struct iio_chan_spec const *chan,
+			int *val, int *val2, long mask)
+{
+	struct mcp47a1_data *data = iio_priv(indio_dev);
+	int ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		ret = i2c_smbus_read_byte_data(data->client, MCP47A1_CMD_CODE);
+		if (ret < 0)
+			return ret;
+
+		*val = ret;
+
+		return IIO_VAL_INT;
+	case IIO_CHAN_INFO_SCALE:
+		*val = data->vref_mV;
+		*val2 = MCP47A1_MAX_STEPS;
+
+		return IIO_VAL_FRACTIONAL;
+	default:
+		return -EINVAL;
+	}
+}
+
+static int mcp47a1_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_RAW:
+		*vals = mcp47a1_raw_avail;
+		*type = IIO_VAL_INT;
+		return IIO_AVAIL_RANGE;
+	default:
+		return -EINVAL;
+	}
+}
+
+static const struct iio_info mcp47a1_info = {
+	.write_raw = mcp47a1_write,
+	.read_raw = mcp47a1_read,
+	.read_avail = mcp47a1_read_avail,
+};
+
+static int mcp47a1_probe(struct i2c_client *client)
+{
+	struct device *dev = &client->dev;
+	struct mcp47a1_data *data;
+	struct iio_dev *indio_dev;
+	int ret;
+
+	indio_dev = devm_iio_device_alloc(dev, sizeof(*data));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	data = iio_priv(indio_dev);
+	data->client = client;
+
+	ret = devm_regulator_get_enable(dev, "vdd");
+	if (ret)
+		return dev_err_probe(dev, ret, "Failed to enable regulator\n");
+
+	/* Delay after device exits reset state (see AC/DC characteristics) */
+	fsleep(20);
+
+	ret = devm_regulator_get_enable_read_voltage(dev, "vref");
+	if (ret < 0)
+		return dev_err_probe(dev, ret, "Failed to read vref\n");
+
+	data->vref_mV = ret / (MICRO / MILLI);
+
+	indio_dev->name = "mcp47a1";
+	indio_dev->modes = INDIO_DIRECT_MODE;
+	indio_dev->info = &mcp47a1_info;
+	indio_dev->channels = &mcp47a1_channel;
+	indio_dev->num_channels = 1;
+
+	return devm_iio_device_register(dev, indio_dev);
+}
+
+static const struct of_device_id mcp47a1_of_match[] = {
+	{ .compatible = "microchip,mcp47a1" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, mcp47a1_of_match);
+
+static const struct i2c_device_id mcp47a1_id[] = {
+	{ .name = "mcp47a1" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, mcp47a1_id);
+
+static struct i2c_driver mcp47a1_driver = {
+	.driver = {
+		.name = "mcp47a1",
+		.of_match_table = mcp47a1_of_match,
+	},
+	.probe = mcp47a1_probe,
+	.id_table = mcp47a1_id,
+};
+module_i2c_driver(mcp47a1_driver);
+
+MODULE_AUTHOR("Joshua Crofts <joshua.crofts1@gmail.com>");
+MODULE_DESCRIPTION("Microchip MCP47A1 DAC Driver");
+MODULE_LICENSE("GPL");

-- 
2.55.0

Re: [PATCH v3 2/2] iio: dac: mcp47a1: add support for new device

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Incorrect SMBus commands send extra bytes and corrupt the DAC hardware state.
--

--- Patch [2]: [PATCH v3 2/2] iio: dac: mcp47a1: add support for new device ---
commit f73263d5ea24798a693c0c4cfa738627794988ba
Author: Joshua Crofts <joshua.crofts1@gmail.com>

iio: dac: mcp47a1: add support for new device

This commit introduces a new driver for the Microchip MCP47A1 6-bit volatile
DAC. It supports writing and reading the raw values and exposing the scale
using I2C.

> diff --git a/drivers/iio/dac/mcp47a1.c b/drivers/iio/dac/mcp47a1.c
> new file mode 100644
> index 0000000000000..0bf994aa0e4f5
> --- /dev/null
> +++ b/drivers/iio/dac/mcp47a1.c

[ ... ]

> +static int mcp47a1_write(struct iio_dev *indio_dev,
> +			 struct iio_chan_spec const *chan,
> +			 int val, int val2, long mask)
> +{
> +	struct mcp47a1_data *data = iio_priv(indio_dev);
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_RAW:
> +		if (!in_range(val, 0, MCP47A1_MAX_STEPS))
> +			return -EINVAL;
> +
> +		return i2c_smbus_write_byte_data(data->client, MCP47A1_CMD_CODE,
> +						 val);

[Severity: Medium]
Could this corrupt the DAC hardware state by sending an extra byte?

If the MCP47A1 expects a single byte without a command code, using
i2c_smbus_write_byte_data() will send a 2-byte payload, writing 0x00 to the
DAC before the actual value. This could potentially cause an output glitch.

> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static int mcp47a1_read(struct iio_dev *indio_dev,
> +			struct iio_chan_spec const *chan,
> +			int *val, int *val2, long mask)
> +{
> +	struct mcp47a1_data *data = iio_priv(indio_dev);
> +	int ret;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_RAW:
> +		ret = i2c_smbus_read_byte_data(data->client, MCP47A1_CMD_CODE);

[Severity: Medium]
Does this destructively reset the DAC on every read?

If the device does not expect a command code and interprets it as a data byte,
calling i2c_smbus_read_byte_data() will perform a write of 0x00 before reading,
destructively resetting the DAC output to 0.

> +		if (ret < 0)
> +			return ret;

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260803-mcp47a1-add-support-v3-0-540e71b4fd2e@gmail.com?part=2

Re: [PATCH v3 2/2] iio: dac: mcp47a1: add support for new device

[Joshua Crofts]

On Mon, 03 Aug 2026 17:44:40 +0000
sashiko-bot@kernel.org wrote:

> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Medium] Incorrect SMBus commands send extra bytes and corrupt the DAC hardware state.
> --
> 
> --- Patch [2]: [PATCH v3 2/2] iio: dac: mcp47a1: add support for new device ---
> commit f73263d5ea24798a693c0c4cfa738627794988ba
> Author: Joshua Crofts <joshua.crofts1@gmail.com>
> 
> iio: dac: mcp47a1: add support for new device
> 
> This commit introduces a new driver for the Microchip MCP47A1 6-bit volatile
> DAC. It supports writing and reading the raw values and exposing the scale
> using I2C.
> 
> > diff --git a/drivers/iio/dac/mcp47a1.c b/drivers/iio/dac/mcp47a1.c
> > new file mode 100644
> > index 0000000000000..0bf994aa0e4f5
> > --- /dev/null
> > +++ b/drivers/iio/dac/mcp47a1.c  
> 
> [ ... ]
> 
> > +static int mcp47a1_write(struct iio_dev *indio_dev,
> > +			 struct iio_chan_spec const *chan,
> > +			 int val, int val2, long mask)
> > +{
> > +	struct mcp47a1_data *data = iio_priv(indio_dev);
> > +
> > +	switch (mask) {
> > +	case IIO_CHAN_INFO_RAW:
> > +		if (!in_range(val, 0, MCP47A1_MAX_STEPS))
> > +			return -EINVAL;
> > +
> > +		return i2c_smbus_write_byte_data(data->client, MCP47A1_CMD_CODE,
> > +						 val);  
> 
> [Severity: Medium]
> Could this corrupt the DAC hardware state by sending an extra byte?
> 
> If the MCP47A1 expects a single byte without a command code, using
> i2c_smbus_write_byte_data() will send a 2-byte payload, writing 0x00 to the
> DAC before the actual value. This could potentially cause an output glitch.
> 
> > +	default:
> > +		return -EINVAL;
> > +	}
> > +}
> > +
> > +static int mcp47a1_read(struct iio_dev *indio_dev,
> > +			struct iio_chan_spec const *chan,
> > +			int *val, int *val2, long mask)
> > +{
> > +	struct mcp47a1_data *data = iio_priv(indio_dev);
> > +	int ret;
> > +
> > +	switch (mask) {
> > +	case IIO_CHAN_INFO_RAW:
> > +		ret = i2c_smbus_read_byte_data(data->client, MCP47A1_CMD_CODE);  
> 
> [Severity: Medium]
> Does this destructively reset the DAC on every read?
> 
> If the device does not expect a command code and interprets it as a data byte,
> calling i2c_smbus_read_byte_data() will perform a write of 0x00 before reading,
> destructively resetting the DAC output to 0.

No, this is a false positive. The MCP47A1 is SMBus compatible, it will interpret
the command as an instruction, not a data byte.

-- 
Kind regards,
Joshua Crofts

Re: [PATCH v3 0/2] iio: dac: mcp47a1: add support for new device

[Jonathan Cameron]

On Mon, 03 Aug 2026 19:32:24 +0200
Joshua Crofts <joshua.crofts1@gmail.com> wrote:

> This patch series adds support for the MCP47A1 DAC.
> 
> The Microchip MCP47A1 is a volatile 6-bit Digital-to-Analog converter
> which communicates via I2C. It is a low-power, low-cost DAC commonly
> used in embedded systems.
> 
> Reasons for adding a new driver:
> - Existing Microchip DACs use a more complicated set of commands
>   whereas the MCP47A1 communicates via SMBus using only one command.
> - The closest Microchip DAC already in the tree - the MCP4725 - uses
>   an EEPROM while the MCP47A1 is volatile, meaning that altering
>   the driver of the former would worsen the code flow.
> - The MCP47A1 maps cleanly to a standard regmap.
> 
> The driver was tested on a Raspberry Pi 4 using a breakout board with
> the MCP47A1.
> 
> The datasheet can be viewed here:
> https://ww1.microchip.com/downloads/aemDocuments/documents/OTH/ProductDocuments/DataSheets/25154A.pdf
> 
> Signed-off-by: Joshua Crofts <joshua.crofts1@gmail.com>
Applied to the testing branch of iio.git

Thanks,

Jonathan