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_HPM 8200 /* see t_MEAS,h in datasheet */ 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_HPM, SHT4X_MEAS_DELAY_HPM + 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, INT_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 * const 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 { 237 struct device *device = &client->dev; 238 struct device *hwmon_dev; 239 struct sht4x_data *data; 240 u8 cmd[] = {SHT4X_CMD_RESET}; 241 int ret; 242 243 /* 244 * we require full i2c support since the sht4x uses multi-byte read and 245 * writes as well as multi-byte commands which are not supported by 246 * the smbus protocol 247 */ 248 if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C)) 249 return -EOPNOTSUPP; 250 251 data = devm_kzalloc(device, sizeof(*data), GFP_KERNEL); 252 if (!data) 253 return -ENOMEM; 254 255 data->update_interval = SHT4X_MIN_POLL_INTERVAL; 256 data->client = client; 257 258 mutex_init(&data->lock); 259 260 crc8_populate_msb(sht4x_crc8_table, SHT4X_CRC8_POLYNOMIAL); 261 262 ret = i2c_master_send(client, cmd, SHT4X_CMD_LEN); 263 if (ret < 0) 264 return ret; 265 if (ret != SHT4X_CMD_LEN) 266 return -EIO; 267 268 hwmon_dev = devm_hwmon_device_register_with_info(device, 269 client->name, 270 data, 271 &sht4x_chip_info, 272 NULL); 273 274 return PTR_ERR_OR_ZERO(hwmon_dev); 275 } 276 277 static const struct i2c_device_id sht4x_id[] = { 278 { "sht4x", 0 }, 279 { }, 280 }; 281 MODULE_DEVICE_TABLE(i2c, sht4x_id); 282 283 static const struct of_device_id sht4x_of_match[] = { 284 { .compatible = "sensirion,sht4x" }, 285 { } 286 }; 287 MODULE_DEVICE_TABLE(of, sht4x_of_match); 288 289 static struct i2c_driver sht4x_driver = { 290 .driver = { 291 .name = "sht4x", 292 .of_match_table = sht4x_of_match, 293 }, 294 .probe_new = sht4x_probe, 295 .id_table = sht4x_id, 296 }; 297 298 module_i2c_driver(sht4x_driver); 299 300 MODULE_AUTHOR("Navin Sankar Velliangiri <navin@linumiz.com>"); 301 MODULE_DESCRIPTION("Sensirion SHT4x humidity and temperature sensor driver"); 302 MODULE_LICENSE("GPL v2"); 303