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

/*
 * aht10.c - Linux hwmon driver for AHT10/AHT20 Temperature and Humidity sensors
 * Copyright (C) 2020 Johannes Cornelis Draaijer
 */

#include <linux/delay.h>
#include <linux/hwmon.h>
#include <linux/i2c.h>
#include <linux/ktime.h>
#include <linux/module.h>
#include <linux/crc8.h>

#define AHT10_MEAS_SIZE         6

#define AHT20_MEAS_SIZE         7
#define AHT20_CRC8_POLY         0x31

/*
 * Poll intervals (in milliseconds)
 */
#define AHT10_DEFAULT_MIN_POLL_INTERVAL 2000
#define AHT10_MIN_POLL_INTERVAL         2000

/*
 * I2C command delays (in microseconds)
 */
#define AHT10_MEAS_DELAY        80000
#define AHT10_CMD_DELAY         350000
#define AHT10_DELAY_EXTRA       100000

/*
 * Command bytes
 */
#define AHT10_CMD_INIT  0b11100001
#define AHT10_CMD_MEAS  0b10101100
#define AHT10_CMD_RST   0b10111010

#define AHT20_CMD_INIT  0b10111110

#define DHT20_CMD_INIT  0b01110001

/*
 * Flags in the answer byte/command
 */
#define AHT10_CAL_ENABLED       BIT(3)
#define AHT10_BUSY              BIT(7)
#define AHT10_MODE_NOR          (BIT(5) | BIT(6))
#define AHT10_MODE_CYC          BIT(5)
#define AHT10_MODE_CMD          BIT(6)

#define AHT10_MAX_POLL_INTERVAL_LEN     30

enum aht10_variant { aht10, aht20, dht20};

static const struct i2c_device_id aht10_id[] = {
        { "aht10", aht10 },
        { "aht20", aht20 },
        { "dht20", dht20 },
        { },
};
MODULE_DEVICE_TABLE(i2c, aht10_id);

/**
 *   struct aht10_data - All the data required to operate an AHT10/AHT20 chip
 *   @client: the i2c client associated with the AHT10/AHT20
 *   @min_poll_interval: the minimum poll interval
 *                   While the poll rate limit is not 100% necessary,
 *                   the datasheet recommends that a measurement
 *                   is not performed too often to prevent
 *                   the chip from warming up due to the heat it generates.
 *                   If it's unwanted, it can be ignored setting it to
 *                   it to 0. Default value is 2000 ms
 *   @previous_poll_time: the previous time that the AHT10/AHT20
 *                        was polled
 *   @temperature: the latest temperature value received from
 *                 the AHT10/AHT20
 *   @humidity: the latest humidity value received from the
 *              AHT10/AHT20
 *   @crc8: crc8 support flag
 *   @meas_size: measurements data size
 *   @init_cmd: Initialization command
 */

struct aht10_data {
        struct i2c_client *client;
        ktime_t min_poll_interval;
        ktime_t previous_poll_time;
        int temperature;
        int humidity;
        bool crc8;
        unsigned int meas_size;
        u8 init_cmd;
};

/*
 * aht10_init() - Initialize an AHT10/AHT20 chip
 * @data: the data associated with this AHT10/AHT20 chip
 * Return: 0 if successful, 1 if not
 */
static int aht10_init(struct aht10_data *data)
{
        const u8 cmd_init[] = {data->init_cmd, AHT10_CAL_ENABLED | AHT10_MODE_CYC,
                               0x00};
        int res;
        u8 status;
        struct i2c_client *client = data->client;

        res = i2c_master_send(client, cmd_init, sizeof(cmd_init));
        if (res < 0)
                return res;

        usleep_range(AHT10_CMD_DELAY, AHT10_CMD_DELAY +
                     AHT10_DELAY_EXTRA);

        res = i2c_master_recv(client, &status, 1);
        if (res != 1)
                return -ENODATA;

        if (status & AHT10_BUSY)
                return -EBUSY;

        return 0;
}

/*
 * aht10_polltime_expired() - check if the minimum poll interval has
 *                                  expired
 * @data: the data containing the time to compare
 * Return: 1 if the minimum poll interval has expired, 0 if not
 */
static int aht10_polltime_expired(struct aht10_data *data)
{
        ktime_t current_time = ktime_get_boottime();
        ktime_t difference = ktime_sub(current_time, data->previous_poll_time);

        return ktime_after(difference, data->min_poll_interval);
}

DECLARE_CRC8_TABLE(crc8_table);

/*
 * crc8_check() - check crc of the sensor's measurements
 * @raw_data: data frame received from sensor(including crc as the last byte)
 * @count: size of the data frame
 * Return: 0 if successful, 1 if not
 */
static int crc8_check(u8 *raw_data, int count)
{
        /*
         * crc calculated on the whole frame(including crc byte) should yield
         * zero in case of correctly received bytes
         */
        return crc8(crc8_table, raw_data, count, CRC8_INIT_VALUE);
}

/*
 * aht10_read_values() - read and parse the raw data from the AHT10/AHT20
 * @data: the struct aht10_data to use for the lock
 * Return: 0 if successful, 1 if not
 */
static int aht10_read_values(struct aht10_data *data)
{
        const u8 cmd_meas[] = {AHT10_CMD_MEAS, 0x33, 0x00};
        u32 temp, hum;
        int res;
        u8 raw_data[AHT20_MEAS_SIZE];
        struct i2c_client *client = data->client;

        if (!aht10_polltime_expired(data))
                return 0;

        res = i2c_master_send(client, cmd_meas, sizeof(cmd_meas));
        if (res < 0)
                return res;

        usleep_range(AHT10_MEAS_DELAY, AHT10_MEAS_DELAY + AHT10_DELAY_EXTRA);

        res = i2c_master_recv(client, raw_data, data->meas_size);
        if (res != data->meas_size) {
                if (res >= 0)
                        return -ENODATA;
                return res;
        }

        if (data->crc8 && crc8_check(raw_data, data->meas_size))
                return -EIO;

        hum =   ((u32)raw_data[1] << 12u) |
                ((u32)raw_data[2] << 4u) |
                ((raw_data[3] & 0xF0u) >> 4u);

        temp =  ((u32)(raw_data[3] & 0x0Fu) << 16u) |
                ((u32)raw_data[4] << 8u) |
                raw_data[5];

        temp = ((temp * 625) >> 15u) * 10;
        hum = ((hum * 625) >> 16u) * 10;

        data->temperature = (int)temp - 50000;
        data->humidity = hum;
        data->previous_poll_time = ktime_get_boottime();

        return 0;
}

/*
 * aht10_interval_write() - store the given minimum poll interval.
 * Return: 0 on success, -EINVAL if a value lower than the
 *         AHT10_MIN_POLL_INTERVAL is given
 */
static ssize_t aht10_interval_write(struct aht10_data *data,
                                    long val)
{
        data->min_poll_interval = ms_to_ktime(clamp_val(val, 2000, LONG_MAX));
        return 0;
}

/*
 * aht10_interval_read() - read the minimum poll interval
 *                            in milliseconds
 */
static ssize_t aht10_interval_read(struct aht10_data *data,
                                   long *val)
{
        *val = ktime_to_ms(data->min_poll_interval);
        return 0;
}

/*
 * aht10_temperature1_read() - read the temperature in millidegrees
 */
static int aht10_temperature1_read(struct aht10_data *data, long *val)
{
        int res;

        res = aht10_read_values(data);
        if (res < 0)
                return res;

        *val = data->temperature;
        return 0;
}

/*
 * aht10_humidity1_read() - read the relative humidity in millipercent
 */
static int aht10_humidity1_read(struct aht10_data *data, long *val)
{
        int res;

        res = aht10_read_values(data);
        if (res < 0)
                return res;

        *val = data->humidity;
        return 0;
}

static umode_t aht10_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 aht10_hwmon_read(struct device *dev, enum hwmon_sensor_types type,
                            u32 attr, int channel, long *val)
{
        struct aht10_data *data = dev_get_drvdata(dev);

        switch (type) {
        case hwmon_temp:
                return aht10_temperature1_read(data, val);
        case hwmon_humidity:
                return aht10_humidity1_read(data, val);
        case hwmon_chip:
                return aht10_interval_read(data, val);
        default:
                return -EOPNOTSUPP;
        }
}

static int aht10_hwmon_write(struct device *dev, enum hwmon_sensor_types type,
                             u32 attr, int channel, long val)
{
        struct aht10_data *data = dev_get_drvdata(dev);

        switch (type) {
        case hwmon_chip:
                return aht10_interval_write(data, val);
        default:
                return -EOPNOTSUPP;
        }
}

static const struct hwmon_channel_info * const aht10_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 aht10_hwmon_ops = {
        .is_visible = aht10_hwmon_visible,
        .read = aht10_hwmon_read,
        .write = aht10_hwmon_write,
};

static const struct hwmon_chip_info aht10_chip_info = {
        .ops = &aht10_hwmon_ops,
        .info = aht10_info,
};

static int aht10_probe(struct i2c_client *client)
{
        enum aht10_variant variant = (uintptr_t)i2c_get_match_data(client);
        struct device *device = &client->dev;
        struct device *hwmon_dev;
        struct aht10_data *data;
        int res;

        if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
                return -ENOENT;

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

        data->min_poll_interval = ms_to_ktime(AHT10_DEFAULT_MIN_POLL_INTERVAL);
        data->client = client;

        switch (variant) {
        case aht20:
                data->meas_size = AHT20_MEAS_SIZE;
                data->crc8 = true;
                crc8_populate_msb(crc8_table, AHT20_CRC8_POLY);
                data->init_cmd = AHT20_CMD_INIT;
                break;
        case dht20:
                data->meas_size = AHT20_MEAS_SIZE;
                data->crc8 = true;
                crc8_populate_msb(crc8_table, AHT20_CRC8_POLY);
                data->init_cmd = DHT20_CMD_INIT;
                break;
        default:
                data->meas_size = AHT10_MEAS_SIZE;
                data->init_cmd = AHT10_CMD_INIT;
                break;
        }

        res = aht10_init(data);
        if (res < 0)
                return res;

        res = aht10_read_values(data);
        if (res < 0)
                return res;

        hwmon_dev = devm_hwmon_device_register_with_info(device,
                                                         client->name,
                                                         data,
                                                         &aht10_chip_info,
                                                         NULL);

        return PTR_ERR_OR_ZERO(hwmon_dev);
}

static struct i2c_driver aht10_driver = {
        .driver = {
                .name = "aht10",
        },
        .probe      = aht10_probe,
        .id_table   = aht10_id,
};

module_i2c_driver(aht10_driver);

MODULE_AUTHOR("Johannes Cornelis Draaijer <jcdra1@gmail.com>");
MODULE_DESCRIPTION("AHT10/AHT20 Temperature and Humidity sensor driver");
MODULE_VERSION("1.0");
MODULE_LICENSE("GPL v2");