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

[PATCH 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>
---
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        |  56 ++++++
 MAINTAINERS                                        |   7 +
 drivers/iio/dac/Kconfig                            |  11 ++
 drivers/iio/dac/Makefile                           |   1 +
 drivers/iio/dac/mcp47a1.c                          | 193 +++++++++++++++++++++
 5 files changed, 268 insertions(+)
---
base-commit: 036d96ceec6d966339aea34d034420991e24cfac
change-id: 20260711-mcp47a1-add-support-3af1248f13a5

Best regards,
-- 
Kind regards,
Joshua Crofts

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

[Joshua Crofts]

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

Signed-off-by: Joshua Crofts <joshua.crofts1@gmail.com>
---
 .../bindings/iio/dac/microchip,mcp47a1.yaml        | 56 ++++++++++++++++++++++
 MAINTAINERS                                        |  6 +++
 2 files changed, 62 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..3322fca03b3a
--- /dev/null
+++ b/Documentation/devicetree/bindings/iio/dac/microchip,mcp47a1.yaml
@@ -0,0 +1,56 @@
+# 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:
+    maxItems: 1
+
+  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>;
+          };
+
+          dac@3e {
+              compatible = "microchip,mcp47a1";
+              reg = <0x3e>;
+              vref-supply = <&vref_regulator>;
+              vdd-supply = <&vdd_regulator>;
+          };
+    };
diff --git a/MAINTAINERS b/MAINTAINERS
index 2b1ec46c5919..b44693593b94 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -17699,6 +17699,12 @@ 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>
+L:	linux-iio@vger.kernel.org
+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 1/2] dt-bindings: iio: dac: add support for mcp47a1

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The binding incorrectly requires `vref-supply`, but the MCP47A1 likely does not have a dedicated VREF pin.
--

--- Patch [1]: [PATCH 1/2] dt-bindings: iio: dac: add support for mcp47a1 ---
commit d1dc3c2e573f4f52e69aabeb608ccb23acd5a123
Author: Joshua Crofts <joshua.crofts1@gmail.com>

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

This commit introduces the device tree bindings and MAINTAINERS entry for
the Microchip MCP47A1, a 6-bit volatile digital-to-analog converter.

> 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..3322fca03b3a7
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/dac/microchip,mcp47a1.yaml
[ ... ]
> +required:
> +  - compatible
> +  - reg
> +  - vref-supply

[Severity: Medium]
Does the MCP47A1 actually have a dedicated VREF pin? Standard Microchip I2C
DACs in this class (such as the 6-pin MCP4725) typically use VDD as their
voltage reference.

If there is no physical VREF pin on this hardware, requiring vref-supply
here forces device tree authors to define dummy regulators in their
device trees just to pass schema validation.

> +  - vdd-supply
> +
> +additionalProperties: false

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260721-mcp47a1-add-support-v1-0-da045a2567e3@gmail.com?part=1

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

[Joshua Crofts]

On Tue, 21 Jul 2026 18:33:58 +0000
sashiko-bot@kernel.org wrote:

Clarifying Sashiko's comment:

> [Severity: Medium]
> Does the MCP47A1 actually have a dedicated VREF pin? Standard Microchip I2C
> DACs in this class (such as the 6-pin MCP4725) typically use VDD as their
> voltage reference.
> 
> If there is no physical VREF pin on this hardware, requiring vref-supply
> here forces device tree authors to define dummy regulators in their
> device trees just to pass schema validation.

Yes, the MCP47A1 does have a physical VREF pin, as seen in the block diagram:
https://ww1.microchip.com/downloads/aemDocuments/documents/OTH/ProductDocuments/DataSheets/25154A.pdf

-- 
Kind regards,
Joshua Crofts

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

[Joshua Crofts]

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

Signed-off-by: Joshua Crofts <joshua.crofts1@gmail.com>
---
 MAINTAINERS               |   1 +
 drivers/iio/dac/Kconfig   |  11 +++
 drivers/iio/dac/Makefile  |   1 +
 drivers/iio/dac/mcp47a1.c | 193 ++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 206 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index b44693593b94..9b124bbdd6ff 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -17704,6 +17704,7 @@ M:	Joshua Crofts <joshua.crofts1@gmail.com>
 L:	linux-iio@vger.kernel.org
 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 17529509da9d..a7f5711e9c3b 100644
--- a/drivers/iio/dac/Kconfig
+++ b/drivers/iio/dac/Kconfig
@@ -563,6 +563,17 @@ 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
+	select REGMAP_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..251c2281634f
--- /dev/null
+++ b/drivers/iio/dac/mcp47a1.c
@@ -0,0 +1,193 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * 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/array_size.h>
+#include <linux/err.h>
+#include <linux/i2c.h>
+#include <linux/module.h>
+#include <linux/regmap.h>
+#include <linux/regulator/consumer.h>
+#include <linux/types.h>
+#include <linux/units.h>
+
+#include <linux/iio/iio.h>
+
+#define MCP47A1_REG_MAX		0x40
+#define MCP47A1_CMD_CODE	0x00
+#define MCP47A1_MAX_STEPS	64
+
+struct mcp47a1_data {
+	struct regmap *regmap;
+	int vref_mv;
+};
+
+static const int mcp47a1_raw_avail[] = { 0, 1, MCP47A1_MAX_STEPS };
+
+static const struct regmap_config mcp47a1_regmap_config = {
+	.name = "mcp47a1",
+	.reg_bits = 8,
+	.val_bits = 8,
+	.max_register = MCP47A1_CMD_CODE,
+};
+
+static const struct iio_chan_spec mcp47a1_channels[] = {
+	{
+		.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 (val < 0 || val > MCP47A1_REG_MAX)
+			return -EINVAL;
+
+		return regmap_write(data->regmap, 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 reg_val;
+	int ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		ret = regmap_read(data->regmap, MCP47A1_CMD_CODE, &reg_val);
+		if (ret)
+			return ret;
+
+		*val = reg_val;
+
+		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 reg_val;
+	int ret;
+
+	indio_dev = devm_iio_device_alloc(dev, sizeof(*data));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	data = iio_priv(indio_dev);
+	i2c_set_clientdata(client, indio_dev);
+
+	data->regmap = devm_regmap_init_i2c(client, &mcp47a1_regmap_config);
+	if (IS_ERR(data->regmap))
+		return dev_err_probe(dev, PTR_ERR(data->regmap),
+				     "Failed to initialize regmap\n");
+
+	ret = devm_regulator_get_enable(dev, "vdd");
+	if (ret)
+		return dev_err_probe(dev, ret, "Failed to enable regulator\n");
+
+	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 / MILLI;
+
+	/*
+	 * This is a volatile DAC which doesn't have an ID register, instead
+	 * the value register is set to 0x20 every Power-on-Reset (table 4-1).
+	 * Any other read value at startup could indicate that the device is
+	 * damaged etc.
+	 */
+	ret = regmap_read(data->regmap, MCP47A1_CMD_CODE, &reg_val);
+	if (ret)
+		return dev_err_probe(dev, ret,
+				     "Failed to read register on startup\n");
+
+	if (reg_val != 0x20)
+		dev_info(dev, "Read value 0x%02x at startup\n", reg_val);
+
+	indio_dev->name = "mcp47a1";
+	indio_dev->modes = INDIO_DIRECT_MODE;
+	indio_dev->info = &mcp47a1_info;
+	indio_dev->channels = mcp47a1_channels;
+	indio_dev->num_channels = ARRAY_SIZE(mcp47a1_channels);
+
+	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("MCP47A1 DAC");
+MODULE_LICENSE("GPL");

-- 
2.55.0

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

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:
- [High] The driver incorrectly allows a maximum raw value of 64 (0x40) to be written to a 6-bit DAC register.
- [High] The driver performs an I2C read immediately after enabling the VDD regulator, without waiting for the device's Power-On Reset (POR) to complete.
- [Medium] The driver requests a non-existent 'vref' regulator instead of using 'vdd' for the reference voltage.
--

--- Patch [2]: [PATCH 2/2] iio: dac: mcp47a1: add support for new device ---
commit 8241b9b8cd61665484502687ea7820769722f397
Author: Joshua Crofts <joshua.crofts1@gmail.com>

iio: dac: mcp47a1: add support for new device

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

> diff --git a/drivers/iio/dac/mcp47a1.c b/drivers/iio/dac/mcp47a1.c
> new file mode 100644
> index 0000000000000..251c2281634ff
> --- /dev/null
> +++ b/drivers/iio/dac/mcp47a1.c
> @@ -0,0 +1,193 @@
[ ... ]
> +#define MCP47A1_REG_MAX		0x40
> +#define MCP47A1_CMD_CODE	0x00
> +#define MCP47A1_MAX_STEPS	64
> +
> +struct mcp47a1_data {
> +	struct regmap *regmap;
> +	int vref_mv;
> +};
> +
> +static const int mcp47a1_raw_avail[] = { 0, 1, MCP47A1_MAX_STEPS };

[Severity: High]
For a 6-bit DAC, the maximum value is 63 (0x3F). Does defining
MCP47A1_REG_MAX to 0x40 (64) allow 7-bit values to bypass validation in
mcp47a1_write() and be written to the register, potentially causing the
data to wrap around or corrupt configuration bits?

[ ... ]
> +static int mcp47a1_probe(struct i2c_client *client)
> +{
[ ... ]
> +	ret = devm_regulator_get_enable(dev, "vdd");
> +	if (ret)
> +		return dev_err_probe(dev, ret, "Failed to enable regulator\n");
> +
> +	ret = devm_regulator_get_enable_read_voltage(dev, "vref");

[Severity: Medium]
Does the MCP47A1 have a dedicated VREF pin? If the hardware derives its
reference voltage from VDD, does requiring a fictitious "vref" regulator
here force device tree authors to mismodel their hardware just to satisfy
the driver?

> +	if (ret < 0)
> +		return dev_err_probe(dev, ret, "Failed to read vref\n");
> +
> +	data->vref_mv = ret / MILLI;
> +
> +	/*
> +	 * This is a volatile DAC which doesn't have an ID register, instead
> +	 * the value register is set to 0x20 every Power-on-Reset (table 4-1).
> +	 * Any other read value at startup could indicate that the device is
> +	 * damaged etc.
> +	 */
> +	ret = regmap_read(data->regmap, MCP47A1_CMD_CODE, &reg_val);

[Severity: High]
Since the VDD regulator is enabled a few lines above, is there a missing
delay to wait for the device's Power-On Reset (POR) to complete? Without
an explicit delay, could this I2C read happen before the internal boot
sequence finishes, potentially resulting in an I2C NACK and probe failure?

> +	if (ret)
> +		return dev_err_probe(dev, ret,
> +				     "Failed to read register on startup\n");

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260721-mcp47a1-add-support-v1-0-da045a2567e3@gmail.com?part=2

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

[Andy Shevchenko]

On Tue, Jul 21, 2026 at 08:24:39PM +0200, Joshua Crofts wrote:
> The Microchip MCP47A1 is a 6-bit volatile Digital-to-Analog converted
> which communicates via I2C.

...

> +#include <linux/array_size.h>
> +#include <linux/err.h>
> +#include <linux/i2c.h>
> +#include <linux/module.h>
> +#include <linux/regmap.h>
> +#include <linux/regulator/consumer.h>
> +#include <linux/types.h>
> +#include <linux/units.h>


> +struct mcp47a1_data {
> +	struct regmap *regmap;
> +	int vref_mv;

_mV

...

> +static const struct regmap_config mcp47a1_regmap_config = {
> +	.name = "mcp47a1",
> +	.reg_bits = 8,
> +	.val_bits = 8,
> +	.max_register = MCP47A1_CMD_CODE,
> +};

No cache?

...

> +static int mcp47a1_probe(struct i2c_client *client)
> +{
> +	struct device *dev = &client->dev;
> +	struct mcp47a1_data *data;
> +	struct iio_dev *indio_dev;
> +	int reg_val;
> +	int ret;
> +
> +	indio_dev = devm_iio_device_alloc(dev, sizeof(*data));
> +	if (!indio_dev)
> +		return -ENOMEM;
> +
> +	data = iio_priv(indio_dev);

> +	i2c_set_clientdata(client, indio_dev);

Is it used?

> +	data->regmap = devm_regmap_init_i2c(client, &mcp47a1_regmap_config);
> +	if (IS_ERR(data->regmap))
> +		return dev_err_probe(dev, PTR_ERR(data->regmap),
> +				     "Failed to initialize regmap\n");
> +
> +	ret = devm_regulator_get_enable(dev, "vdd");
> +	if (ret)
> +		return dev_err_probe(dev, ret, "Failed to enable regulator\n");
> +
> +	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 / MILLI;

(MICRO / MILLI)

> +	/*
> +	 * This is a volatile DAC which doesn't have an ID register, instead
> +	 * the value register is set to 0x20 every Power-on-Reset (table 4-1).
> +	 * Any other read value at startup could indicate that the device is
> +	 * damaged etc.
> +	 */
> +	ret = regmap_read(data->regmap, MCP47A1_CMD_CODE, &reg_val);
> +	if (ret)
> +		return dev_err_probe(dev, ret,
> +				     "Failed to read register on startup\n");
> +
> +	if (reg_val != 0x20)
> +		dev_info(dev, "Read value 0x%02x at startup\n", reg_val);
> +
> +	indio_dev->name = "mcp47a1";
> +	indio_dev->modes = INDIO_DIRECT_MODE;
> +	indio_dev->info = &mcp47a1_info;
> +	indio_dev->channels = mcp47a1_channels;
> +	indio_dev->num_channels = ARRAY_SIZE(mcp47a1_channels);
> +
> +	return devm_iio_device_register(dev, indio_dev);
> +}

-- 
With Best Regards,
Andy Shevchenko