sht4x.c

// SPDX-License-Identifier: GPL-2.0-only

/*
 * Copyright (c) Linumiz 2021
 *
 * sht4x.c - Linux hwmon driver for SHT4x Temperature and Humidity sensor
 *
 * Author: Navin Sankar Velliangiri <navin@linumiz.com>
 */

#include <linux/crc8.h>
#include <linux/delay.h>
#include <linux/hwmon.h>
#include <linux/hwmon-sysfs.h>
#include <linux/i2c.h>
#include <linux/jiffies.h>
#include <linux/module.h>

/*
 * Poll intervals (in milliseconds)
 */
#define SHT4X_MIN_POLL_INTERVAL	2000

/*
 * I2C command delays (in microseconds)
 */
#define SHT4X_MEAS_DELAY_HPM	8200	/* see t_MEAS,h in datasheet */
#define SHT4X_DELAY_EXTRA	10000

/*
 * Command Bytes
 */
#define SHT4X_CMD_MEASURE_HPM	0b11111101
#define SHT4X_CMD_RESET		0b10010100
#define SHT4X_CMD_HEATER_20_1	0b00011110
#define SHT4X_CMD_HEATER_20_01	0b00010101
#define SHT4X_CMD_HEATER_110_1	0b00101111
#define SHT4X_CMD_HEATER_110_01	0b00100100
#define SHT4X_CMD_HEATER_200_1	0b00111001
#define SHT4X_CMD_HEATER_200_01 0b00110010

#define SHT4X_CMD_LEN		1
#define SHT4X_CRC8_LEN		1
#define SHT4X_WORD_LEN		2
#define SHT4X_RESPONSE_LENGTH	6
#define SHT4X_CRC8_POLYNOMIAL	0x31
#define SHT4X_CRC8_INIT		0xff
#define SHT4X_MIN_TEMPERATURE	-45000
#define SHT4X_MAX_TEMPERATURE	125000
#define SHT4X_MIN_HUMIDITY	0
#define SHT4X_MAX_HUMIDITY	100000

DECLARE_CRC8_TABLE(sht4x_crc8_table);

/**
 * struct sht4x_data - All the data required to operate an SHT4X chip
 * @client: the i2c client associated with the SHT4X
 * @lock: a mutex that is used to prevent parallel access to the i2c client
 * @heating_complete: the time that the last heating finished
 * @data_pending: true if and only if there are measurements to retrieve after heating
 * @heater_power: the power at which the heater will be started
 * @heater_time: the time for which the heater will remain turned on
 * @valid: validity of fields below
 * @update_interval: the minimum poll interval
 * @last_updated: the previous time that the SHT4X was polled
 * @temperature: the latest temperature value received from the SHT4X
 * @humidity: the latest humidity value received from the SHT4X
 */
struct sht4x_data {
	struct i2c_client	*client;
	struct mutex		lock;	/* atomic read data updates */
	unsigned long		heating_complete;	/* in jiffies */
	bool			data_pending;
	u32			heater_power;	/* in milli-watts */
	u32			heater_time;	/* in milli-seconds */
	bool			valid;	/* validity of fields below */
	long			update_interval;	/* in milli-seconds */
	long			last_updated;	/* in jiffies */
	s32			temperature;
	s32			humidity;
};

/**
 * sht4x_read_values() - read and parse the raw data from the SHT4X
 * @data: the struct sht4x_data to use for the lock
 * Return: 0 if successful, -ERRNO if not
 */
static int sht4x_read_values(struct sht4x_data *data)
{
	int ret = 0;
	u16 t_ticks, rh_ticks;
	unsigned long next_update;
	struct i2c_client *client = data->client;
	u8 crc;
	u8 cmd[SHT4X_CMD_LEN] = {SHT4X_CMD_MEASURE_HPM};
	u8 raw_data[SHT4X_RESPONSE_LENGTH];
	unsigned long curr_jiffies;

	mutex_lock(&data->lock);

	curr_jiffies = jiffies;
	if (time_before(curr_jiffies, data->heating_complete))
		msleep(jiffies_to_msecs(data->heating_complete - curr_jiffies));

	if (data->data_pending &&
	    time_before(jiffies, data->heating_complete + data->update_interval)) {
		data->data_pending = false;
	} else {
		next_update = data->last_updated +
			msecs_to_jiffies(data->update_interval);

		if (data->valid && time_before_eq(jiffies, next_update))
			goto unlock;

		ret = i2c_master_send(client, cmd, SHT4X_CMD_LEN);
		if (ret < 0)
			goto unlock;

		usleep_range(SHT4X_MEAS_DELAY_HPM, SHT4X_MEAS_DELAY_HPM + SHT4X_DELAY_EXTRA);
	}

	ret = i2c_master_recv(client, raw_data, SHT4X_RESPONSE_LENGTH);
	if (ret != SHT4X_RESPONSE_LENGTH) {
		if (ret >= 0)
			ret = -ENODATA;
		goto unlock;
	}

	t_ticks = raw_data[0] << 8 | raw_data[1];
	rh_ticks = raw_data[3] << 8 | raw_data[4];

	crc = crc8(sht4x_crc8_table, &raw_data[0], SHT4X_WORD_LEN, CRC8_INIT_VALUE);
	if (crc != raw_data[2]) {
		dev_err(&client->dev, "data integrity check failed\n");
		ret = -EIO;
		goto unlock;
	}

	crc = crc8(sht4x_crc8_table, &raw_data[3], SHT4X_WORD_LEN, CRC8_INIT_VALUE);
	if (crc != raw_data[5]) {
		dev_err(&client->dev, "data integrity check failed\n");
		ret = -EIO;
		goto unlock;
	}

	data->temperature = ((21875 * (int32_t)t_ticks) >> 13) - 45000;
	data->humidity = ((15625 * (int32_t)rh_ticks) >> 13) - 6000;
	data->last_updated = jiffies;
	data->valid = true;
	ret = 0;

unlock:
	mutex_unlock(&data->lock);
	return ret;
}

static ssize_t sht4x_interval_write(struct sht4x_data *data, long val)
{
	data->update_interval = clamp_val(val, SHT4X_MIN_POLL_INTERVAL, INT_MAX);

	return 0;
}

/* sht4x_interval_read() - read the minimum poll interval in milliseconds */
static size_t sht4x_interval_read(struct sht4x_data *data, long *val)
{
	*val = data->update_interval;
	return 0;
}

/* sht4x_temperature1_read() - read the temperature in millidegrees */
static int sht4x_temperature1_read(struct sht4x_data *data, long *val)
{
	int ret;

	ret = sht4x_read_values(data);
	if (ret < 0)
		return ret;

	*val = data->temperature;

	return 0;
}

/* sht4x_humidity1_read() - read a relative humidity in millipercent */
static int sht4x_humidity1_read(struct sht4x_data *data, long *val)
{
	int ret;

	ret = sht4x_read_values(data);
	if (ret < 0)
		return ret;

	*val = data->humidity;

	return 0;
}

static umode_t sht4x_hwmon_visible(const void *data,
				   enum hwmon_sensor_types type,
				   u32 attr, int channel)
{
	switch (type) {
	case hwmon_temp:
	case hwmon_humidity:
		return 0444;
	case hwmon_chip:
		return 0644;
	default:
		return 0;
	}
}

static int sht4x_hwmon_read(struct device *dev, enum hwmon_sensor_types type,
			    u32 attr, int channel, long *val)
{
	struct sht4x_data *data = dev_get_drvdata(dev);

	switch (type) {
	case hwmon_temp:
		return sht4x_temperature1_read(data, val);
	case hwmon_humidity:
		return sht4x_humidity1_read(data, val);
	case hwmon_chip:
		return sht4x_interval_read(data, val);
	default:
		return -EOPNOTSUPP;
	}
}

static int sht4x_hwmon_write(struct device *dev, enum hwmon_sensor_types type,
			     u32 attr, int channel, long val)
{
	struct sht4x_data *data = dev_get_drvdata(dev);

	switch (type) {
	case hwmon_chip:
		return sht4x_interval_write(data, val);
	default:
		return -EOPNOTSUPP;
	}
}

static ssize_t heater_enable_show(struct device *dev,
				  struct device_attribute *attr,
				  char *buf)
{
	struct sht4x_data *data = dev_get_drvdata(dev);

	return sysfs_emit(buf, "%u\n", time_before(jiffies, data->heating_complete));
}

static ssize_t heater_enable_store(struct device *dev,
				   struct device_attribute *attr,
				   const char *buf,
				   size_t count)
{
	struct sht4x_data *data = dev_get_drvdata(dev);
	bool status;
	ssize_t ret;
	u8 cmd;
	u32 heating_time_bound;

	ret = kstrtobool(buf, &status);
	if (ret)
		return ret;
	if (!status)
		return -EINVAL;

	if (data->heater_time == 100) {
		if (data->heater_power == 20)
			cmd = SHT4X_CMD_HEATER_20_01;
		else if (data->heater_power == 110)
			cmd = SHT4X_CMD_HEATER_110_01;
		else /* data->heater_power == 200 */
			cmd = SHT4X_CMD_HEATER_200_01;

		heating_time_bound = 110;
	} else { /* data->heater_time == 1000 */
		if (data->heater_power == 20)
			cmd = SHT4X_CMD_HEATER_20_1;
		else if (data->heater_power == 110)
			cmd = SHT4X_CMD_HEATER_110_1;
		else /* data->heater_power == 200 */
			cmd = SHT4X_CMD_HEATER_200_1;

		heating_time_bound = 1100;
	}

	mutex_lock(&data->lock);

	if (time_before(jiffies, data->heating_complete)) {
		ret = -EBUSY;
		goto unlock;
	}

	ret = i2c_master_send(data->client, &cmd, SHT4X_CMD_LEN);
	if (ret < 0)
		goto unlock;

	data->heating_complete = jiffies + msecs_to_jiffies(heating_time_bound);
	data->data_pending = true;
unlock:
	mutex_unlock(&data->lock);
	return ret;
}

static ssize_t heater_power_show(struct device *dev,
				 struct device_attribute *attr,
				 char *buf)
{
	struct sht4x_data *data = dev_get_drvdata(dev);

	return sysfs_emit(buf, "%u\n", data->heater_power);
}

static ssize_t heater_power_store(struct device *dev,
				  struct device_attribute *attr,
				  const char *buf,
				  size_t count)
{
	struct sht4x_data *data = dev_get_drvdata(dev);
	u32 power;
	ssize_t ret;

	ret = kstrtou32(buf, 10, &power);
	if (ret)
		return ret;

	if (power != 20 && power != 110 && power != 200)
		return -EINVAL;

	data->heater_power = power;

	return count;
}

static ssize_t heater_time_show(struct device *dev,
				struct device_attribute *attr,
				char *buf)
{
	struct sht4x_data *data = dev_get_drvdata(dev);

	return sysfs_emit(buf, "%u\n", data->heater_time);
}

static ssize_t heater_time_store(struct device *dev,
				 struct device_attribute *attr,
				 const char *buf,
				 size_t count)
{
	struct sht4x_data *data = dev_get_drvdata(dev);
	u32 time;
	ssize_t ret;

	ret = kstrtou32(buf, 10, &time);
	if (ret)
		return ret;

	if (time != 100 && time != 1000)
		return -EINVAL;

	data->heater_time = time;

	return count;
}

static DEVICE_ATTR_RW(heater_enable);
static DEVICE_ATTR_RW(heater_power);
static DEVICE_ATTR_RW(heater_time);

static struct attribute *sht4x_attrs[] = {
	&dev_attr_heater_enable.attr,
	&dev_attr_heater_power.attr,
	&dev_attr_heater_time.attr,
	NULL
};

ATTRIBUTE_GROUPS(sht4x);

static const struct hwmon_channel_info * const sht4x_info[] = {
	HWMON_CHANNEL_INFO(chip, HWMON_C_UPDATE_INTERVAL),
	HWMON_CHANNEL_INFO(temp, HWMON_T_INPUT),
	HWMON_CHANNEL_INFO(humidity, HWMON_H_INPUT),
	NULL,
};

static const struct hwmon_ops sht4x_hwmon_ops = {
	.is_visible = sht4x_hwmon_visible,
	.read = sht4x_hwmon_read,
	.write = sht4x_hwmon_write,
};

static const struct hwmon_chip_info sht4x_chip_info = {
	.ops = &sht4x_hwmon_ops,
	.info = sht4x_info,
};

static int sht4x_probe(struct i2c_client *client)
{
	struct device *device = &client->dev;
	struct device *hwmon_dev;
	struct sht4x_data *data;
	u8 cmd[] = {SHT4X_CMD_RESET};
	int ret;

	/*
	 * we require full i2c support since the sht4x uses multi-byte read and
	 * writes as well as multi-byte commands which are not supported by
	 * the smbus protocol
	 */
	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
		return -EOPNOTSUPP;

	data = devm_kzalloc(device, sizeof(*data), GFP_KERNEL);
	if (!data)
		return -ENOMEM;

	data->update_interval = SHT4X_MIN_POLL_INTERVAL;
	data->client = client;
	data->heater_power = 200;
	data->heater_time = 1000;
	data->heating_complete = jiffies;

	mutex_init(&data->lock);

	crc8_populate_msb(sht4x_crc8_table, SHT4X_CRC8_POLYNOMIAL);

	ret = i2c_master_send(client, cmd, SHT4X_CMD_LEN);
	if (ret < 0)
		return ret;
	if (ret != SHT4X_CMD_LEN)
		return -EIO;

	hwmon_dev = devm_hwmon_device_register_with_info(device,
							 client->name,
							 data,
							 &sht4x_chip_info,
							 sht4x_groups);

	return PTR_ERR_OR_ZERO(hwmon_dev);
}

static const struct i2c_device_id sht4x_id[] = {
	{ "sht4x" },
	{ },
};
MODULE_DEVICE_TABLE(i2c, sht4x_id);

static const struct of_device_id sht4x_of_match[] = {
	{ .compatible = "sensirion,sht4x" },
	{ }
};
MODULE_DEVICE_TABLE(of, sht4x_of_match);

static struct i2c_driver sht4x_driver = {
	.driver = {
		.name = "sht4x",
		.of_match_table = sht4x_of_match,
	},
	.probe		= sht4x_probe,
	.id_table	= sht4x_id,
};

module_i2c_driver(sht4x_driver);

MODULE_AUTHOR("Navin Sankar Velliangiri <navin@linumiz.com>");
MODULE_DESCRIPTION("Sensirion SHT4x humidity and temperature sensor driver");
MODULE_LICENSE("GPL v2");