drivers/hwmon/sht4x.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2
   3 /*
   4  * Copyright (c) Linumiz 2021
   5  *
   6  * sht4x.c - Linux hwmon driver for SHT4x Temperature and Humidity sensor
   7  *
   8  * Author: Navin Sankar Velliangiri <navin@linumiz.com>
   9  */
  10
  11 #include <linux/crc8.h>
  12 #include <linux/delay.h>
  13 #include <linux/hwmon.h>
  14 #include <linux/i2c.h>
  15 #include <linux/jiffies.h>
  16 #include <linux/module.h>
  17
  18 /*
  19  * Poll intervals (in milliseconds)
  20  */
  21 #define SHT4X_MIN_POLL_INTERVAL 2000
  22
  23 /*
  24  * I2C command delays (in microseconds)
  25  */
  26 #define SHT4X_MEAS_DELAY        1000
  27 #define SHT4X_DELAY_EXTRA       10000
  28
  29 /*
  30  * Command Bytes
  31  */
  32 #define SHT4X_CMD_MEASURE_HPM   0b11111101
  33 #define SHT4X_CMD_RESET         0b10010100
  34
  35 #define SHT4X_CMD_LEN           1
  36 #define SHT4X_CRC8_LEN          1
  37 #define SHT4X_WORD_LEN          2
  38 #define SHT4X_RESPONSE_LENGTH   6
  39 #define SHT4X_CRC8_POLYNOMIAL   0x31
  40 #define SHT4X_CRC8_INIT         0xff
  41 #define SHT4X_MIN_TEMPERATURE   -45000
  42 #define SHT4X_MAX_TEMPERATURE   125000
  43 #define SHT4X_MIN_HUMIDITY      0
  44 #define SHT4X_MAX_HUMIDITY      100000
  45
  46 DECLARE_CRC8_TABLE(sht4x_crc8_table);
  47
  48 /**
  49  * struct sht4x_data - All the data required to operate an SHT4X chip
  50  * @client: the i2c client associated with the SHT4X
  51  * @lock: a mutex that is used to prevent parallel access to the i2c client
  52  * @update_interval: the minimum poll interval
  53  * @last_updated: the previous time that the SHT4X was polled
  54  * @temperature: the latest temperature value received from the SHT4X
  55  * @humidity: the latest humidity value received from the SHT4X
  56  */
  57 struct sht4x_data {
  58         struct i2c_client       *client;
  59         struct mutex            lock;   /* atomic read data updates */
  60         bool                    valid;  /* validity of fields below */
  61         long                    update_interval;        /* in milli-seconds */
  62         long                    last_updated;   /* in jiffies */
  63         s32                     temperature;
  64         s32                     humidity;
  65 };
  66
  67 /**
  68  * sht4x_read_values() - read and parse the raw data from the SHT4X
  69  * @sht4x_data: the struct sht4x_data to use for the lock
  70  * Return: 0 if successful, -ERRNO if not
  71  */
  72 static int sht4x_read_values(struct sht4x_data *data)
  73 {
  74         int ret = 0;
  75         u16 t_ticks, rh_ticks;
  76         unsigned long next_update;
  77         struct i2c_client *client = data->client;
  78         u8 crc;
  79         u8 cmd[SHT4X_CMD_LEN] = {SHT4X_CMD_MEASURE_HPM};
  80         u8 raw_data[SHT4X_RESPONSE_LENGTH];
  81
  82         mutex_lock(&data->lock);
  83         next_update = data->last_updated +
  84                       msecs_to_jiffies(data->update_interval);
  85
  86         if (data->valid && time_before_eq(jiffies, next_update))
  87                 goto unlock;
  88
  89         ret = i2c_master_send(client, cmd, SHT4X_CMD_LEN);
  90         if (ret < 0)
  91                 goto unlock;
  92
  93         usleep_range(SHT4X_MEAS_DELAY, SHT4X_MEAS_DELAY + SHT4X_DELAY_EXTRA);
  94
  95         ret = i2c_master_recv(client, raw_data, SHT4X_RESPONSE_LENGTH);
  96         if (ret != SHT4X_RESPONSE_LENGTH) {
  97                 if (ret >= 0)
  98                         ret = -ENODATA;
  99                 goto unlock;
 100         }
 101
 102         t_ticks = raw_data[0] << 8 | raw_data[1];
 103         rh_ticks = raw_data[3] << 8 | raw_data[4];
 104
 105         crc = crc8(sht4x_crc8_table, &raw_data[0], SHT4X_WORD_LEN, CRC8_INIT_VALUE);
 106         if (crc != raw_data[2]) {
 107                 dev_err(&client->dev, "data integrity check failed\n");
 108                 ret = -EIO;
 109                 goto unlock;
 110         }
 111
 112         crc = crc8(sht4x_crc8_table, &raw_data[3], SHT4X_WORD_LEN, CRC8_INIT_VALUE);
 113         if (crc != raw_data[5]) {
 114                 dev_err(&client->dev, "data integrity check failed\n");
 115                 ret = -EIO;
 116                 goto unlock;
 117         }
 118
 119         data->temperature = ((21875 * (int32_t)t_ticks) >> 13) - 45000;
 120         data->humidity = ((15625 * (int32_t)rh_ticks) >> 13) - 6000;
 121         data->last_updated = jiffies;
 122         data->valid = true;
 123         ret = 0;
 124
 125 unlock:
 126         mutex_unlock(&data->lock);
 127         return ret;
 128 }
 129
 130 static ssize_t sht4x_interval_write(struct sht4x_data *data, long val)
 131 {
 132         data->update_interval = clamp_val(val, SHT4X_MIN_POLL_INTERVAL, UINT_MAX);
 133
 134         return 0;
 135 }
 136
 137 /* sht4x_interval_read() - read the minimum poll interval in milliseconds */
 138 static size_t sht4x_interval_read(struct sht4x_data *data, long *val)
 139 {
 140         *val = data->update_interval;
 141         return 0;
 142 }
 143
 144 /* sht4x_temperature1_read() - read the temperature in millidegrees */
 145 static int sht4x_temperature1_read(struct sht4x_data *data, long *val)
 146 {
 147         int ret;
 148
 149         ret = sht4x_read_values(data);
 150         if (ret < 0)
 151                 return ret;
 152
 153         *val = data->temperature;
 154
 155         return 0;
 156 }
 157
 158 /* sht4x_humidity1_read() - read a relative humidity in millipercent */
 159 static int sht4x_humidity1_read(struct sht4x_data *data, long *val)
 160 {
 161         int ret;
 162
 163         ret = sht4x_read_values(data);
 164         if (ret < 0)
 165                 return ret;
 166
 167         *val = data->humidity;
 168
 169         return 0;
 170 }
 171
 172 static umode_t sht4x_hwmon_visible(const void *data,
 173                                    enum hwmon_sensor_types type,
 174                                    u32 attr, int channel)
 175 {
 176         switch (type) {
 177         case hwmon_temp:
 178         case hwmon_humidity:
 179                 return 0444;
 180         case hwmon_chip:
 181                 return 0644;
 182         default:
 183                 return 0;
 184         }
 185 }
 186
 187 static int sht4x_hwmon_read(struct device *dev, enum hwmon_sensor_types type,
 188                             u32 attr, int channel, long *val)
 189 {
 190         struct sht4x_data *data = dev_get_drvdata(dev);
 191
 192         switch (type) {
 193         case hwmon_temp:
 194                 return sht4x_temperature1_read(data, val);
 195         case hwmon_humidity:
 196                 return sht4x_humidity1_read(data, val);
 197         case hwmon_chip:
 198                 return sht4x_interval_read(data, val);
 199         default:
 200                 return -EOPNOTSUPP;
 201         }
 202 }
 203
 204 static int sht4x_hwmon_write(struct device *dev, enum hwmon_sensor_types type,
 205                              u32 attr, int channel, long val)
 206 {
 207         struct sht4x_data *data = dev_get_drvdata(dev);
 208
 209         switch (type) {
 210         case hwmon_chip:
 211                 return sht4x_interval_write(data, val);
 212         default:
 213                 return -EOPNOTSUPP;
 214         }
 215 }
 216
 217 static const struct hwmon_channel_info *sht4x_info[] = {
 218         HWMON_CHANNEL_INFO(chip, HWMON_C_UPDATE_INTERVAL),
 219         HWMON_CHANNEL_INFO(temp, HWMON_T_INPUT),
 220         HWMON_CHANNEL_INFO(humidity, HWMON_H_INPUT),
 221         NULL,
 222 };
 223
 224 static const struct hwmon_ops sht4x_hwmon_ops = {
 225         .is_visible = sht4x_hwmon_visible,
 226         .read = sht4x_hwmon_read,
 227         .write = sht4x_hwmon_write,
 228 };
 229
 230 static const struct hwmon_chip_info sht4x_chip_info = {
 231         .ops = &sht4x_hwmon_ops,
 232         .info = sht4x_info,
 233 };
 234
 235 static int sht4x_probe(struct i2c_client *client,
 236                        const struct i2c_device_id *sht4x_id)
 237 {
 238         struct device *device = &client->dev;
 239         struct device *hwmon_dev;
 240         struct sht4x_data *data;
 241         u8 cmd[] = {SHT4X_CMD_RESET};
 242         int ret;
 243
 244         /*
 245          * we require full i2c support since the sht4x uses multi-byte read and
 246          * writes as well as multi-byte commands which are not supported by
 247          * the smbus protocol
 248          */
 249         if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
 250                 return -EOPNOTSUPP;
 251
 252         data = devm_kzalloc(device, sizeof(*data), GFP_KERNEL);
 253         if (!data)
 254                 return -ENOMEM;
 255
 256         data->update_interval = SHT4X_MIN_POLL_INTERVAL;
 257         data->client = client;
 258
 259         mutex_init(&data->lock);
 260
 261         crc8_populate_msb(sht4x_crc8_table, SHT4X_CRC8_POLYNOMIAL);
 262
 263         ret = i2c_master_send(client, cmd, SHT4X_CMD_LEN);
 264         if (ret < 0)
 265                 return ret;
 266         if (ret != SHT4X_CMD_LEN)
 267                 return -EIO;
 268
 269         hwmon_dev = devm_hwmon_device_register_with_info(device,
 270                                                          client->name,
 271                                                          data,
 272                                                          &sht4x_chip_info,
 273                                                          NULL);
 274
 275         return PTR_ERR_OR_ZERO(hwmon_dev);
 276 }
 277
 278 static const struct i2c_device_id sht4x_id[] = {
 279         { "sht4x", 0 },
 280         { },
 281 };
 282 MODULE_DEVICE_TABLE(i2c, sht4x_id);
 283
 284 static struct i2c_driver sht4x_driver = {
 285         .driver = {
 286                 .name = "sht4x",
 287         },
 288         .probe          = sht4x_probe,
 289         .id_table       = sht4x_id,
 290 };
 291
 292 module_i2c_driver(sht4x_driver);
 293
 294 MODULE_AUTHOR("Navin Sankar Velliangiri <navin@linumiz.com>");
 295 MODULE_DESCRIPTION("Sensirion SHT4x humidity and temperature sensor driver");
 296 MODULE_LICENSE("GPL v2");