iio: temperature: Add MCP9600 thermocouple EMF converter

Add support for the MCP9600 thermocouple electromotive force converter. The sensor has  integrated cold junction compensation and a typical accuracy of 0.5 degrees Celsius. The driver supports a resolution of 0.0625 degrees Celsius.

Datasheet: https://ww1.microchip.com/downloads/en/DeviceDoc/MCP960X-Data-Sheet-20005426.pdf
Signed-off-by: Andrew Hepp <andrew.hepp@ahepp.dev>
Link: https://lore.kernel.org/r/20231025233153.5454-2-andrew.hepp@ahepp.dev
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/temperature/Kconfig

@@ -158,4 +158,14 @@ config MAX31865
 	  This driver can also be build as a module. If so, the module
 	  will be called max31865.
 
+config MCP9600
+	tristate "MCP9600 thermocouple EMF converter"
+	depends on I2C
+	help
+	  If you say yes here you get support for MCP9600
+	  thermocouple EMF converter connected via I2C.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called mcp9600.
+
 endmenu

drivers/iio/temperature/Makefile

@@ -10,6 +10,7 @@ obj-$(CONFIG_MAXIM_THERMOCOUPLE) += maxim_thermocouple.o
 obj-$(CONFIG_MAX30208) += max30208.o
 obj-$(CONFIG_MAX31856) += max31856.o
 obj-$(CONFIG_MAX31865) += max31865.o
+obj-$(CONFIG_MCP9600) += mcp9600.o
 obj-$(CONFIG_MLX90614) += mlx90614.o
 obj-$(CONFIG_MLX90632) += mlx90632.o
 obj-$(CONFIG_TMP006) += tmp006.o

drivers/iio/temperature/mcp9600.c

@@ -0,0 +1,139 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * mcp9600.c - Support for Microchip MCP9600 thermocouple EMF converter
+ *
+ * Copyright (c) 2022 Andrew Hepp
+ * Author: <andrew.hepp@ahepp.dev>
+ */
+
+#include <linux/err.h>
+#include <linux/i2c.h>
+#include <linux/init.h>
+#include <linux/mod_devicetable.h>
+#include <linux/module.h>
+
+#include <linux/iio/iio.h>
+
+/* MCP9600 registers */
+#define MCP9600_HOT_JUNCTION 0x0
+#define MCP9600_COLD_JUNCTION 0x2
+#define MCP9600_DEVICE_ID 0x20
+
+/* MCP9600 device id value */
+#define MCP9600_DEVICE_ID_MCP9600 0x40
+
+static const struct iio_chan_spec mcp9600_channels[] = {
+	{
+		.type = IIO_TEMP,
+		.address = MCP9600_HOT_JUNCTION,
+		.info_mask_separate =
+			BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),
+	},
+	{
+		.type = IIO_TEMP,
+		.address = MCP9600_COLD_JUNCTION,
+		.channel2 = IIO_MOD_TEMP_AMBIENT,
+		.modified = 1,
+		.info_mask_separate =
+			BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),
+	},
+};
+
+struct mcp9600_data {
+	struct i2c_client *client;
+};
+
+static int mcp9600_read(struct mcp9600_data *data,
+			struct iio_chan_spec const *chan, int *val)
+{
+	int ret;
+
+	ret = i2c_smbus_read_word_swapped(data->client, chan->address);
+
+	if (ret < 0)
+		return ret;
+	*val = ret;
+
+	return 0;
+}
+
+static int mcp9600_read_raw(struct iio_dev *indio_dev,
+			    struct iio_chan_spec const *chan, int *val,
+			    int *val2, long mask)
+{
+	struct mcp9600_data *data = iio_priv(indio_dev);
+	int ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		ret = mcp9600_read(data, chan, val);
+		if (ret)
+			return ret;
+		return IIO_VAL_INT;
+	case IIO_CHAN_INFO_SCALE:
+		*val = 62;
+		*val2 = 500000;
+		return IIO_VAL_INT_PLUS_MICRO;
+	default:
+		return -EINVAL;
+	}
+}
+
+static const struct iio_info mcp9600_info = {
+	.read_raw = mcp9600_read_raw,
+};
+
+static int mcp9600_probe(struct i2c_client *client)
+{
+	struct iio_dev *indio_dev;
+	struct mcp9600_data *data;
+	int ret;
+
+	ret = i2c_smbus_read_byte_data(client, MCP9600_DEVICE_ID);
+	if (ret < 0)
+		return dev_err_probe(&client->dev, ret, "Failed to read device ID\n");
+	if (ret != MCP9600_DEVICE_ID_MCP9600)
+		dev_warn(&client->dev, "Expected ID %x, got %x\n",
+				MCP9600_DEVICE_ID_MCP9600, ret);
+
+	indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*data));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	data = iio_priv(indio_dev);
+	data->client = client;
+
+	indio_dev->info = &mcp9600_info;
+	indio_dev->name = "mcp9600";
+	indio_dev->modes = INDIO_DIRECT_MODE;
+	indio_dev->channels = mcp9600_channels;
+	indio_dev->num_channels = ARRAY_SIZE(mcp9600_channels);
+
+	return devm_iio_device_register(&client->dev, indio_dev);
+}
+
+static const struct i2c_device_id mcp9600_id[] = {
+	{ "mcp9600" },
+	{}
+};
+MODULE_DEVICE_TABLE(i2c, mcp9600_id);
+
+static const struct of_device_id mcp9600_of_match[] = {
+	{ .compatible = "microchip,mcp9600" },
+	{}
+};
+MODULE_DEVICE_TABLE(of, mcp9600_of_match);
+
+static struct i2c_driver mcp9600_driver = {
+	.driver = {
+		.name = "mcp9600",
+		.of_match_table = mcp9600_of_match,
+	},
+	.probe = mcp9600_probe,
+	.id_table = mcp9600_id
+};
+module_i2c_driver(mcp9600_driver);
+
+MODULE_AUTHOR("Andrew Hepp <andrew.hepp@ahepp.dev>");
+MODULE_DESCRIPTION("Microchip MCP9600 thermocouple EMF converter driver");
+MODULE_LICENSE("GPL");