iio: adc: Add initial support for MAX22531 ADC

Add device support for MAX22530-MAX22531.
Implement scale and read functionality for raw/filtered ADC readings.

Signed-off-by: Abhinav Jain <jain.abhinav177@gmail.com>

Author: psychild

MAINTAINERS

@@ -13058,6 +13058,7 @@ L:	linux-iio@vger.kernel.org
 S:	Maintained
 W:	https://ez.analog.com/linux-software-drivers
 F:	Documentation/devicetree/bindings/iio/adc/adi,max22531.yaml
+F:	drivers/iio/adc/max22531.c
 
 MAX31827 TEMPERATURE SWITCH DRIVER
 M:	Daniel Matyas <daniel.matyas@analog.com>

drivers/iio/adc/Kconfig

@@ -1126,6 +1126,16 @@ config MAX1363
 	  To compile this driver as a module, choose M here: the module will be
 	  called max1363.
 
+config MAX22531
+        tristate "Analog Devices MAX22531 ADC Driver"
+        depends on SPI
+        help
+          Say yes here to build support for field-side self-powered 12-bit
+	  isolated Maxim ADCs. (max22530, max22531, max22532).
+
+	  To compile this driver as a module, choose M here: the module will be
+	  called max22531.
+
 config MAX77541_ADC
 	tristate "Analog Devices MAX77541 ADC driver"
 	depends on MFD_MAX77541

drivers/iio/adc/Makefile

@@ -156,6 +156,7 @@ obj-$(CONFIG_MAX11205) += max11205.o
 obj-$(CONFIG_MAX11410) += max11410.o
 obj-$(CONFIG_MAX1241) += max1241.o
 obj-$(CONFIG_MAX1363) += max1363.o
+obj-$(CONFIG_MAX22531) += max22531.o
 obj-$(CONFIG_MAX77541_ADC) += max77541-adc.o
 obj-$(CONFIG_MAX9611) += max9611.o
 obj-$(CONFIG_MCP320X) += mcp320x.o

drivers/iio/adc/max22531.c

@@ -0,0 +1,190 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * MAX22531 SPI ADC Driver
+ *
+ * Copyright (C) 2025 Abhinav Jain
+ *
+ * Datasheet: https://www.analog.com/media/en/technical-documentation/data-sheets/max22530-max22532.pdf
+ */
+
+#include <linux/units.h>
+#include <linux/module.h>
+#include <asm/unaligned.h>
+#include <linux/spi/spi.h>
+#include <linux/iio/iio.h>
+#include <linux/regulator/consumer.h>
+
+#define MAX22531_REG_PROD_ID		0x00
+#define MAX22531_REG_ADC_CHAN(x)	((x) + 1)
+#define MAX22531_REG_FADC_CHAN(x)	((x) + 1)
+
+#define MAX22531_VREF_MV		(18 * MILLI)
+#define MAX22531_DEVICE_REV_MSK		GENMASK(6, 0)
+#define MAX22531_DEVICE_REV		0x01
+
+#define MAX22531_REG_ADDR_MASK		GENMASK(7, 2)
+#define MAX22531_REG_WRITE_MASK		BIT(1)
+
+enum max22531_id {
+	max22530,
+	max22531,
+	max22532,
+};
+
+struct max22531_chip_info {
+	const char *name;
+};
+
+static struct max22531_chip_info max22531_chip_info_tbl[] = {
+	[max22530] = {
+		.name = "max22530",
+	},
+	[max22531] = {
+		.name = "max22531",
+	},
+	[max22532] = {
+		.name = "max22532",
+	},
+};
+
+struct max22531 {
+	struct spi_device *spi_dev;
+	const struct max22531_chip_info *chip_info;
+};
+
+#define MAX22531_CHANNEL(ch)						\
+	{								\
+		.type = IIO_VOLTAGE,					\
+		.indexed = 1,						\
+		.channel = (ch),					\
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |		\
+				BIT(IIO_CHAN_INFO_AVERAGE_RAW),         \
+		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),	\
+	}
+
+static const struct iio_chan_spec max22531_channels[] = {
+	MAX22531_CHANNEL(0),
+	MAX22531_CHANNEL(1),
+	MAX22531_CHANNEL(2),
+	MAX22531_CHANNEL(3),
+};
+
+static int max22531_reg_read(struct max22531 *adc, unsigned int reg,
+			     unsigned int *readval)
+{
+	u8 cmd;
+
+	cmd = FIELD_PREP(MAX22531_REG_ADDR_MASK, reg);
+	*readval = spi_w8r16be(adc->spi_dev, cmd);
+	if (*readval < 0)
+		return *readval;
+
+	return 0;
+}
+
+static int max22531_read_raw(struct iio_dev *indio_dev,
+			     struct iio_chan_spec const *chan,
+			     int *val, int *val2, long mask)
+{
+	struct max22531 *adc = iio_priv(indio_dev);
+	int ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		ret = max22531_reg_read(adc, MAX22531_REG_ADC_CHAN(chan->channel), val);
+		if (ret)
+			return ret;
+	return IIO_VAL_INT;
+
+	case IIO_CHAN_INFO_AVERAGE_RAW:
+		ret = max22531_reg_read(adc, MAX22531_REG_FADC_CHAN(chan->channel), val);
+		if (ret)
+			return ret;
+		return IIO_VAL_INT;
+
+	case IIO_CHAN_INFO_SCALE:
+		*val = MAX22531_VREF_MV;
+		*val2 = 12;
+
+		return IIO_VAL_FRACTIONAL_LOG2;
+
+	default:
+		return -EINVAL;
+	}
+}
+
+static const struct iio_info max22531_info = {
+	.read_raw = max22531_read_raw,
+};
+
+static int max22531_probe(struct spi_device *spi)
+{
+	const struct max22531_chip_info *chip_info;
+	struct iio_dev *indio_dev;
+	struct max22531 *adc;
+	unsigned int prod_id;
+	int ret;
+
+	indio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*adc));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	adc = iio_priv(indio_dev);
+	adc->spi_dev = spi;
+	adc->chip_info = chip_info;
+
+	indio_dev->name = adc->chip_info->name;
+	indio_dev->info = &max22531_info;
+	indio_dev->channels = max22531_channels;
+	indio_dev->num_channels = ARRAY_SIZE(max22531_channels);
+
+	ret = devm_regulator_get_enable(&spi->dev, "vddl");
+	if (ret)
+		return dev_err_probe(&spi->dev, ret,
+		       "Failed to retrieve power logic supply.\n");
+
+	ret = devm_regulator_get_enable(&spi->dev, "vddpl");
+	if (ret)
+		return dev_err_probe(&spi->dev, ret,
+		       "Failed to retrieve isolated DC-DC supply.\n");
+
+	ret = max22531_reg_read(adc, MAX22531_REG_PROD_ID, &prod_id);
+	if (ret ||
+	    FIELD_GET(MAX22531_DEVICE_REV_MSK, prod_id) != MAX22531_DEVICE_REV)
+		dev_warn(&spi->dev, "PROD_ID verification failed\n");
+
+	return devm_iio_device_register(&spi->dev, indio_dev);
+}
+
+static const struct spi_device_id max22531_id[] = {
+	{ "max22530", (kernel_ulong_t)&max22531_chip_info_tbl[max22530] },
+	{ "max22531", (kernel_ulong_t)&max22531_chip_info_tbl[max22531] },
+	{ "max22532", (kernel_ulong_t)&max22531_chip_info_tbl[max22532] },
+	{ }
+};
+MODULE_DEVICE_TABLE(spi, max22531_id);
+
+static const struct of_device_id max22531_spi_of_id[] = {
+	{ .compatible = "adi,max22530",
+		.data = &max22531_chip_info_tbl[max22530], },
+	{ .compatible = "adi,max22531",
+		.data = &max22531_chip_info_tbl[max22531], },
+	{ .compatible = "adi,max22532",
+		.data = &max22531_chip_info_tbl[max22532], },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, max22531_spi_of_id);
+
+static struct spi_driver max22531_driver = {
+	.driver = {
+		.name = "max22531",
+		.of_match_table = max22531_spi_of_id,
+	},
+	.probe		= max22531_probe,
+	.id_table	= max22531_id,
+};
+module_spi_driver(max22531_driver);
+
+MODULE_AUTHOR("Abhinav Jain <jain.abhinav177@gmail.com>");
+MODULE_DESCRIPTION("MAX22531 ADC");
+MODULE_LICENSE("GPL");