iio: humidity: Add support for Sensirion SHTC3 sensor

The SHTC3 is a digital humidity and temperature sensor.
It covers humidity measurement range from 0 to 100% relative humidity
and temperature measurement range from -45 to 125 deg C.

Datasheet: https://www.sensirion.com/file/datasheet_shtc3

Signed-off-by: Gilles Talis <gilles.talis@gmail.com>

drivers/iio/humidity/Kconfig

@@ -98,6 +98,17 @@ config HTU21
 	  This driver can also be built as a module. If so, the module will
 	  be called htu21.
 
+config SHTC3
+	tristate "Sensirion SHTC3 humidity and temperature sensor"
+	depends on I2C
+	select CRC8
+	help
+	  Say yes here to build support for the Sensirion SHTC3
+	  humidity and temperature sensor.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called shtc3.
+
 config SI7005
 	tristate "SI7005 relative humidity and temperature sensor"
 	depends on I2C

drivers/iio/humidity/Makefile

@@ -16,6 +16,7 @@ obj-$(CONFIG_HTS221_I2C) += hts221_i2c.o
 obj-$(CONFIG_HTS221_SPI) += hts221_spi.o
 
 obj-$(CONFIG_HTU21) += htu21.o
+obj-$(CONFIG_SHTC3) += shtc3.o
 obj-$(CONFIG_SI7005) += si7005.o
 obj-$(CONFIG_SI7020) += si7020.o
 

drivers/iio/humidity/shtc3.c

@@ -0,0 +1,286 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Sensirion SHTC3 Humidity and Temperature Sensor
+ *
+ * Copyright (c) 2021 Gilles Talis <gilles.talis@gmail.com>
+ *
+ * Datasheet: https://www.sensirion.com/file/datasheet_shtc3
+ *
+ * I2C slave address: 0x70
+ */
+
+#include <linux/crc8.h>
+#include <linux/delay.h>
+#include <linux/i2c.h>
+#include <linux/module.h>
+#include <linux/mod_devicetable.h>
+
+#include <linux/iio/iio.h>
+
+#define SHTC3_CMD(cmd_word)		cpu_to_be16(cmd_word)
+#define SHTC3_CMD_LEN			2
+
+#define SHTC3_ID_MASK			0x083F
+#define SHTC3_ID			0x0807
+
+#define SHTC3_CRC8_POLYNOMIAL		0x31
+
+enum shtc3_cmd {
+	SHTC3_CMD_GET_ID		= SHTC3_CMD(0xEFC8),
+	SHTC3_CMD_SOFT_RESET		= SHTC3_CMD(0x805D),
+	SHTC3_CMD_SLEEP			= SHTC3_CMD(0xB098),
+	SHTC3_CMD_WAKEUP		= SHTC3_CMD(0x3517),
+	/*
+	 * Run measurement, low-power mode, clock stretching
+	 * temperature first
+	 */
+	SHTC3_CMD_TEMP_MEAS_LP_CS	= SHTC3_CMD(0x6458),
+	/*
+	 * Run measurement, low-power mode, clock stretching
+	 * relative humidity first
+	 */
+	SHTC3_CMD_RH_MEAS_LP_CS		= SHTC3_CMD(0x44DE),
+};
+
+DECLARE_CRC8_TABLE(shtc3_crc8_tbl);
+
+struct shtc3_rx_data {
+	__be16	data;
+	u8	crc;
+} __packed;
+
+static int shtc3_send_cmd(struct i2c_client *client, u16 cmd, u16 *data)
+{
+	int ret;
+	struct shtc3_rx_data rx_data;
+	u8 crc;
+
+	ret = i2c_master_send(client, (const char *)&cmd, SHTC3_CMD_LEN);
+	if (ret != SHTC3_CMD_LEN)
+		return -EIO;
+
+	/*
+	 * This is used to read temperature and humidity measurements
+	 * as well as the sensor ID.
+	 * Sensor sends 2 bytes of data followed by one byte of CRC
+	 */
+	if (data) {
+		ret = i2c_master_recv(client, (u8 *) &rx_data,
+					sizeof(struct shtc3_rx_data));
+		if (ret < 0)
+			return ret;
+		if (ret != sizeof(struct shtc3_rx_data))
+			return -EIO;
+
+		crc = crc8(shtc3_crc8_tbl, (u8 *)&rx_data.data,
+			    2, CRC8_INIT_VALUE);
+		if (crc != rx_data.crc)
+			return -EIO;
+
+		*data = be16_to_cpu(rx_data.data);
+	}
+
+	return 0;
+}
+
+static int shtc3_sleep(struct i2c_client *client)
+{
+	return shtc3_send_cmd(client, SHTC3_CMD_SLEEP, 0);
+}
+
+static int shtc3_wakeup(struct i2c_client *client)
+{
+	if (shtc3_send_cmd(client, SHTC3_CMD_WAKEUP, 0) < 0)
+		return -EIO;
+
+	/* Wait for device to wake up */
+	usleep_range(180, 240);
+
+	return 0;
+}
+
+static int shtc3_read_channel(struct i2c_client *client, bool temp)
+{
+	int ret;
+	u16 cmd;
+	u16 meas;
+
+	ret = shtc3_wakeup(client);
+	if (ret < 0)
+		return ret;
+
+	/*
+	 * Sensor sends back measurement results after measurement command
+	 * has been issued by the host.
+	 * Sensor sends 3 bytes (2 bytes of data + 1 byte of CRC) for each
+	 * channel sequentially
+	 * The command issued by the host determines the channel for which
+	 * the sensor will first send the data.
+	 * We select the channel for which we need the results
+	 * then only read back the 2 bytes corresponding to this channel.
+	 */
+	cmd = temp ? SHTC3_CMD_TEMP_MEAS_LP_CS : SHTC3_CMD_RH_MEAS_LP_CS;
+	ret = shtc3_send_cmd(client, cmd, &meas);
+	if (ret < 0)
+		return ret;
+
+	/* Go back to sleep */
+	shtc3_sleep(client);
+
+	return meas;
+}
+
+static int shtc3_read_raw(struct iio_dev *indio_dev,
+			   struct iio_chan_spec const *chan, int *val,
+			   int *val2, long mask)
+{
+	struct i2c_client **client = iio_priv(indio_dev);
+	int ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		ret = shtc3_read_channel(*client, (chan->type == IIO_TEMP));
+		if (ret < 0)
+			return ret;
+		*val = ret;
+		return IIO_VAL_INT;
+	case IIO_CHAN_INFO_SCALE:
+		if (chan->type == IIO_TEMP) {
+			*val = 2;
+			*val2 = 670000;
+		} else {
+			*val = 0;
+			*val2 = 1525;
+		}
+		return IIO_VAL_INT_PLUS_MICRO;
+	case IIO_CHAN_INFO_OFFSET:
+		*val = -16852;
+		return IIO_VAL_INT;
+	default:
+		break;
+	}
+
+	return -EINVAL;
+}
+
+static const struct iio_chan_spec shtc3_channels[] = {
+	{
+		.type = IIO_HUMIDITYRELATIVE,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+			BIT(IIO_CHAN_INFO_SCALE),
+	},
+	{
+		.type = IIO_TEMP,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+			BIT(IIO_CHAN_INFO_SCALE) | BIT(IIO_CHAN_INFO_OFFSET),
+	}
+};
+
+static const struct iio_info shtc3_info = {
+	.read_raw = shtc3_read_raw,
+};
+
+static int shtc3_verify_id(struct i2c_client *client)
+{
+	int ret;
+	u16 device_id;
+	u16 reg_val;
+
+	ret = shtc3_send_cmd(client, SHTC3_CMD_GET_ID, &reg_val);
+	if (ret < 0)
+		return ret;
+
+	device_id = reg_val & SHTC3_ID_MASK;
+	if (device_id != SHTC3_ID)
+		return -ENODEV;
+
+	return 0;
+}
+
+static int shtc3_reset(struct i2c_client *client)
+{
+	int ret;
+
+	ret = shtc3_send_cmd(client, SHTC3_CMD_SOFT_RESET, 0);
+	if (ret < 0)
+		return ret;
+
+	/* Wait for device to enter idle state */
+	usleep_range(180, 240);
+
+	return 0;
+}
+
+static int shtc3_setup(struct i2c_client *client)
+{
+	int ret;
+
+	ret = shtc3_verify_id(client);
+	if (ret < 0) {
+		dev_err(&client->dev, "SHTC3 not found\n");
+		return -ENODEV;
+	}
+
+	ret = shtc3_reset(client);
+	if (ret < 0)
+		return ret;
+
+	return shtc3_sleep(client);
+}
+
+static int shtc3_probe(struct i2c_client *client,
+			const struct i2c_device_id *id)
+{
+	struct iio_dev *indio_dev;
+	struct i2c_client **data;
+	int ret;
+
+	indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*data));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	data = iio_priv(indio_dev);
+	*data = client;
+
+	indio_dev->name = dev_name(&client->dev);
+	indio_dev->modes = INDIO_DIRECT_MODE;
+	indio_dev->info = &shtc3_info;
+	indio_dev->channels = shtc3_channels;
+	indio_dev->num_channels = ARRAY_SIZE(shtc3_channels);
+
+	crc8_populate_msb(shtc3_crc8_tbl, SHTC3_CRC8_POLYNOMIAL);
+
+	ret = shtc3_setup(client);
+	if (ret < 0) {
+		dev_err(&client->dev, "SHTC3 setup failed\n");
+		return ret;
+	}
+
+	return devm_iio_device_register(&client->dev, indio_dev);
+}
+
+static const struct i2c_device_id shtc3_id[] = {
+	{ "shtc3", 0 },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, shtc3_id);
+
+static const struct of_device_id shtc3_dt_ids[] = {
+	{ .compatible = "sensirion,shtc3" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, shtc3_dt_ids);
+
+static struct i2c_driver shtc3_driver = {
+	.driver = {
+		.name = "shtc3",
+		.of_match_table = shtc3_dt_ids,
+	},
+	.probe		= shtc3_probe,
+	.id_table	= shtc3_id,
+};
+
+module_i2c_driver(shtc3_driver);
+MODULE_DESCRIPTION("Sensirion SHTC3 Humidity and Temperature Sensor");
+MODULE_AUTHOR("Gilles Talis <gilles.talis@gmail.com>");
+MODULE_LICENSE("GPL");