// 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        1000
#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, SHT4X_MEAS_DELAY + 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 struct i2c_driver sht4x_driver = {
        .driver = {
                .name = "sht4x",
        },
        .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");