iio: temperature: Add driver support for Maxim MAX30208

Maxim MAX30208 is a digital temperature sensor with 0.1°C accuracy.

Add support for max30208 driver in iio subsystem.

Datasheet: https://datasheets.maximintegrated.com/en/ds/MAX30208.pdf
Signed-off-by: Rajat Khandelwal <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

MAINTAINERS

···
 F:	Documentation/devicetree/bindings/regulator/maxim,max20086.yaml
 F:	drivers/regulator/max20086-regulator.c
 
+MAXIM MAX30208 TEMPERATURE SENSOR DRIVER
+M:	Rajat Khandelwal <[e-mail]>
+L:	[e-mail]
+S:	Maintained
+F:	drivers/iio/temperature/max30208.c
+
 MAXIM MAX77650 PMIC MFD DRIVER
 M:	Bartosz Golaszewski <[e-mail]>
 L:	[e-mail]

drivers/iio/temperature/Kconfig

···
 	  This driver can also be built as a module. If so, the module will
 	  be called tsys02d.
 
+config MAX30208
+	tristate "Maxim MAX30208 digital temperature sensor"
+	depends on I2C
+	help
+	  If you say yes here you get support for Maxim MAX30208
+	  digital temperature sensor connected via I2C.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called max30208.
+
 config MAX31856
 	tristate "MAX31856 thermocouple sensor"
 	depends on SPI

drivers/iio/temperature/Makefile

···
 obj-$(CONFIG_LTC2983) += ltc2983.o
 obj-$(CONFIG_HID_SENSOR_TEMP) += hid-sensor-temperature.o
 obj-$(CONFIG_MAXIM_THERMOCOUPLE) += maxim_thermocouple.o
+obj-$(CONFIG_MAX30208) += max30208.o
 obj-$(CONFIG_MAX31856) += max31856.o
 obj-$(CONFIG_MAX31865) += max31865.o
 obj-$(CONFIG_MLX90614) += mlx90614.o

drivers/iio/temperature/max30208.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+
+/*
+ * Copyright (c) Rajat Khandelwal <[e-mail]>
+ *
+ * Maxim MAX30208 digital temperature sensor with 0.1°C accuracy
+ * (7-bit I2C slave address (0x50 - 0x53))
+ */
+
+#include <linux/bitops.h>
+#include <linux/delay.h>
+#include <linux/iio/iio.h>
+#include <linux/i2c.h>
+#include <linux/module.h>
+#include <linux/types.h>
+
+#define MAX30208_STATUS			0x00
+#define MAX30208_STATUS_TEMP_RDY	BIT(0)
+#define MAX30208_INT_ENABLE		0x01
+#define MAX30208_INT_ENABLE_TEMP_RDY	BIT(0)
+
+#define MAX30208_FIFO_OVF_CNTR		0x06
+#define MAX30208_FIFO_DATA_CNTR		0x07
+#define MAX30208_FIFO_DATA		0x08
+
+#define MAX30208_FIFO_CONFIG		0x0a
+#define MAX30208_FIFO_CONFIG_RO		BIT(1)
+
+#define MAX30208_SYSTEM_CTRL		0x0c
+#define MAX30208_SYSTEM_CTRL_RESET	0x01
+
+#define MAX30208_TEMP_SENSOR_SETUP	0x14
+#define MAX30208_TEMP_SENSOR_SETUP_CONV	BIT(0)
+
+struct max30208_data {
+	struct i2c_client *client;
+	struct iio_dev *indio_dev;
+	struct mutex lock; /* Lock to prevent concurrent reads of temperature readings */
+};
+
+static const struct iio_chan_spec max30208_channels[] = {
+	{
+		.type = IIO_TEMP,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),
+	},
+};
+
+/**
+ * max30208_request() - Request a reading
+ * @data: Struct comprising member elements of the device
+ *
+ * Requests a reading from the device and waits until the conversion is ready.
+ */
+static int max30208_request(struct max30208_data *data)
+{
+	/*
+	 * Sensor can take up to 500 ms to respond so execute a total of
+	 * 10 retries to give the device sufficient time.
+	 */
+	int retries = 10;
+	u8 regval;
+	int ret;
+
+	ret = i2c_smbus_read_byte_data(data->client, MAX30208_TEMP_SENSOR_SETUP);
+	if (ret < 0)
+		return ret;
+
+	regval = ret | MAX30208_TEMP_SENSOR_SETUP_CONV;
+
+	ret = i2c_smbus_write_byte_data(data->client, MAX30208_TEMP_SENSOR_SETUP, regval);
+	if (ret)
+		return ret;
+
+	while (retries--) {
+		ret = i2c_smbus_read_byte_data(data->client, MAX30208_STATUS);
+		if (ret < 0)
+			return ret;
+
+		if (ret & MAX30208_STATUS_TEMP_RDY)
+			return 0;
+
+		msleep(50);
+	}
+	dev_err(&data->client->dev, "Temperature conversion failed\n");
+
+	return -ETIMEDOUT;
+}
+
+static int max30208_update_temp(struct max30208_data *data)
+{
+	u8 data_count;
+	int ret;
+
+	mutex_lock(&data->lock);
+
+	ret = max30208_request(data);
+	if (ret)
+		goto unlock;
+
+	ret = i2c_smbus_read_byte_data(data->client, MAX30208_FIFO_OVF_CNTR);
+	if (ret < 0)
+		goto unlock;
+	else if (!ret) {
+		ret = i2c_smbus_read_byte_data(data->client, MAX30208_FIFO_DATA_CNTR);
+		if (ret < 0)
+			goto unlock;
+
+		data_count = ret;
+	} else
+		data_count = 1;
+
+	while (data_count) {
+		ret = i2c_smbus_read_word_swapped(data->client, MAX30208_FIFO_DATA);
+		if (ret < 0)
+			goto unlock;
+
+		data_count--;
+	}
+
+unlock:
+	mutex_unlock(&data->lock);
+	return ret;
+}
+
+/**
+ * max30208_config_setup() - Set up FIFO configuration register
+ * @data: Struct comprising member elements of the device
+ *
+ * Sets the rollover bit to '1' to enable overwriting FIFO during overflow.
+ */
+static int max30208_config_setup(struct max30208_data *data)
+{
+	u8 regval;
+	int ret;
+
+	ret = i2c_smbus_read_byte_data(data->client, MAX30208_FIFO_CONFIG);
+	if (ret < 0)
+		return ret;
+
+	regval = ret | MAX30208_FIFO_CONFIG_RO;
+
+	ret = i2c_smbus_write_byte_data(data->client, MAX30208_FIFO_CONFIG, regval);
+	if (ret)
+		return ret;
+
+	return 0;
+}
+
+static int max30208_read(struct iio_dev *indio_dev,
+			 struct iio_chan_spec const *chan,
+			 int *val, int *val2, long mask)
+{
+	struct max30208_data *data = iio_priv(indio_dev);
+	int ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		ret = max30208_update_temp(data);
+		if (ret < 0)
+			return ret;
+
+		*val = sign_extend32(ret, 15);
+		return IIO_VAL_INT;
+
+	case IIO_CHAN_INFO_SCALE:
+		*val = 5;
+		return IIO_VAL_INT;
+
+	default:
+		return -EINVAL;
+	}
+}
+
+static const struct iio_info max30208_info = {
+	.read_raw = max30208_read,
+};
+
+static int max30208_probe(struct i2c_client *i2c)
+{
+	struct device *dev = &i2c->dev;
+	struct max30208_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 = i2c;
+	mutex_init(&data->lock);
+
+	indio_dev->name = "max30208";
+	indio_dev->channels = max30208_channels;
+	indio_dev->num_channels = ARRAY_SIZE(max30208_channels);
+	indio_dev->info = &max30208_info;
+	indio_dev->modes = INDIO_DIRECT_MODE;
+
+	ret = i2c_smbus_write_byte_data(data->client, MAX30208_SYSTEM_CTRL,
+					MAX30208_SYSTEM_CTRL_RESET);
+	if (ret) {
+		dev_err(dev, "Failure in performing reset\n");
+		return ret;
+	}
+
+	msleep(50);
+
+	ret = max30208_config_setup(data);
+	if (ret)
+		return ret;
+
+	ret = devm_iio_device_register(dev, indio_dev);
+	if (ret) {
+		dev_err(dev, "Failed to register IIO device\n");
+		return ret;
+	}
+
+	return 0;
+}
+
+static const struct i2c_device_id max30208_id_table[] = {
+	{ "max30208" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, max30208_id_table);
+
+static const struct acpi_device_id max30208_acpi_match[] = {
+	{ "MAX30208" },
+	{ }
+};
+MODULE_DEVICE_TABLE(acpi, max30208_acpi_match);
+
+static const struct of_device_id max30208_of_match[] = {
+	{ .compatible = "maxim,max30208" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, max30208_of_match);
+
+static struct i2c_driver max30208_driver = {
+	.driver = {
+		.name = "max30208",
+		.of_match_table = max30208_of_match,
+		.acpi_match_table = max30208_acpi_match,
+	},
+	.probe_new = max30208_probe,
+	.id_table = max30208_id_table,
+};
+module_i2c_driver(max30208_driver);
+
+MODULE_AUTHOR("Rajat Khandelwal <[e-mail]>");
+MODULE_DESCRIPTION("Maxim MAX30208 digital temperature sensor");
+MODULE_LICENSE("GPL");