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// 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/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_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
* @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 */
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
* @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];
mutex_lock(&data->lock);
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, UINT_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 const struct hwmon_channel_info *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,
const struct i2c_device_id *sht4x_id)
{
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;
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,
NULL);
return PTR_ERR_OR_ZERO(hwmon_dev);
}
static const struct i2c_device_id sht4x_id[] = {
{ "sht4x", 0 },
{ },
};
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");