[PATCH v2 0/2] iio: dac: mcp47a1: add support for new device

[PATCH v2 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 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                          | 169 +++++++++++++++++++++
 5 files changed, 236 insertions(+)
---
base-commit: 0506462caaecb179708657142575823177c83783
change-id: 20260711-mcp47a1-add-support-3af1248f13a5

Best regards,
-- 
Kind regards,
Joshua Crofts

[PATCH v2 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 bcdc00999ef8..8a0b23418a64 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

[PATCH v2 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 | 169 ++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 181 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 8a0b23418a64..552ced65cf75 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 d6d560c09e25..1d00cd911826 100644
--- a/drivers/iio/dac/Kconfig
+++ b/drivers/iio/dac/Kconfig
@@ -565,6 +565,16 @@ 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..140e93ff2ba0
--- /dev/null
+++ b/drivers/iio/dac/mcp47a1.c
@@ -0,0 +1,169 @@
+// 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/delay.h>
+#include <linux/err.h>
+#include <linux/i2c.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_REG_MAX		0x40
+#define MCP47A1_CMD_CODE	0x00
+#define MCP47A1_MAX_STEP	63
+
+struct mcp47a1_data {
+	struct i2c_client *client;
+	int vref_mV;
+};
+
+static const int mcp47a1_raw_avail[] = { 0, 1, MCP47A1_MAX_STEP };
+
+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_MAX_STEP)
+			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_STEP;
+
+		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_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 v2 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] Potential off-by-one in DAC scale calculation denominator.
--

--- Patch [2]: [PATCH v2 2/2] iio: dac: mcp47a1: add support for new device ---
commit 38bec2fbb020c3f749c52a26e5cc3e78e72eeaf5
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 converter
which communicates via I2C.

> diff --git a/drivers/iio/dac/mcp47a1.c b/drivers/iio/dac/mcp47a1.c
> new file mode 100644
> index 0000000000000..140e93ff2ba01
> --- /dev/null
> +++ b/drivers/iio/dac/mcp47a1.c
[ ... ]
> +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_SCALE:
> +		*val = data->vref_mV;
> +		*val2 = MCP47A1_MAX_STEP;

[Severity: Medium]
Does this code use the correct denominator for the scale calculation?

Since this is a 6-bit DAC, shouldn't the scale denominator be 64 (2^6)
instead of the maximum step value of 63? Using MCP47A1_MAX_STEP (63) here
introduces an off-by-one error that could cause userspace to calculate
output voltages with a ~1.5% LSB scaling error when reading the sysfs
attribute.

> +
> +		return IIO_VAL_FRACTIONAL;
> +	default:
> +		return -EINVAL;
> +	}
> +}

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260727-mcp47a1-add-support-v2-0-d4591a2ce69e@gmail.com?part=2