1 // SPDX-License-Identifier: GPL-2.0-or-later 2 /* Sensirion SHT21 humidity and temperature sensor driver 3 * 4 * Copyright (C) 2010 Urs Fleisch <urs.fleisch@sensirion.com> 5 * 6 * Data sheet available at https://www.sensirion.com/file/datasheet_sht21 7 */ 8 9 #include <linux/module.h> 10 #include <linux/init.h> 11 #include <linux/slab.h> 12 #include <linux/i2c.h> 13 #include <linux/hwmon.h> 14 #include <linux/hwmon-sysfs.h> 15 #include <linux/err.h> 16 #include <linux/mutex.h> 17 #include <linux/device.h> 18 #include <linux/jiffies.h> 19 20 /* I2C command bytes */ 21 #define SHT21_TRIG_T_MEASUREMENT_HM 0xe3 22 #define SHT21_TRIG_RH_MEASUREMENT_HM 0xe5 23 #define SHT21_READ_SNB_CMD1 0xFA 24 #define SHT21_READ_SNB_CMD2 0x0F 25 #define SHT21_READ_SNAC_CMD1 0xFC 26 #define SHT21_READ_SNAC_CMD2 0xC9 27 28 /** 29 * struct sht21 - SHT21 device specific data 30 * @client: I2C client device 31 * @lock: mutex to protect measurement values 32 * @last_update: time of last update (jiffies) 33 * @temperature: cached temperature measurement value 34 * @humidity: cached humidity measurement value 35 * @valid: only 0 before first measurement is taken 36 * @eic: cached electronic identification code text 37 */ 38 struct sht21 { 39 struct i2c_client *client; 40 struct mutex lock; 41 unsigned long last_update; 42 int temperature; 43 int humidity; 44 bool valid; 45 char eic[18]; 46 }; 47 48 /** 49 * sht21_temp_ticks_to_millicelsius() - convert raw temperature ticks to 50 * milli celsius 51 * @ticks: temperature ticks value received from sensor 52 */ 53 static inline int sht21_temp_ticks_to_millicelsius(int ticks) 54 { 55 ticks &= ~0x0003; /* clear status bits */ 56 /* 57 * Formula T = -46.85 + 175.72 * ST / 2^16 from data sheet 6.2, 58 * optimized for integer fixed point (3 digits) arithmetic 59 */ 60 return ((21965 * ticks) >> 13) - 46850; 61 } 62 63 /** 64 * sht21_rh_ticks_to_per_cent_mille() - convert raw humidity ticks to 65 * one-thousandths of a percent relative humidity 66 * @ticks: humidity ticks value received from sensor 67 */ 68 static inline int sht21_rh_ticks_to_per_cent_mille(int ticks) 69 { 70 ticks &= ~0x0003; /* clear status bits */ 71 /* 72 * Formula RH = -6 + 125 * SRH / 2^16 from data sheet 6.1, 73 * optimized for integer fixed point (3 digits) arithmetic 74 */ 75 return ((15625 * ticks) >> 13) - 6000; 76 } 77 78 /** 79 * sht21_update_measurements() - get updated measurements from device 80 * @dev: device 81 * 82 * Returns 0 on success, else negative errno. 83 */ 84 static int sht21_update_measurements(struct device *dev) 85 { 86 int ret = 0; 87 struct sht21 *sht21 = dev_get_drvdata(dev); 88 struct i2c_client *client = sht21->client; 89 90 mutex_lock(&sht21->lock); 91 /* 92 * Data sheet 2.4: 93 * SHT2x should not be active for more than 10% of the time - e.g. 94 * maximum two measurements per second at 12bit accuracy shall be made. 95 */ 96 if (time_after(jiffies, sht21->last_update + HZ / 2) || !sht21->valid) { 97 ret = i2c_smbus_read_word_swapped(client, 98 SHT21_TRIG_T_MEASUREMENT_HM); 99 if (ret < 0) 100 goto out; 101 sht21->temperature = sht21_temp_ticks_to_millicelsius(ret); 102 ret = i2c_smbus_read_word_swapped(client, 103 SHT21_TRIG_RH_MEASUREMENT_HM); 104 if (ret < 0) 105 goto out; 106 sht21->humidity = sht21_rh_ticks_to_per_cent_mille(ret); 107 sht21->last_update = jiffies; 108 sht21->valid = true; 109 } 110 out: 111 mutex_unlock(&sht21->lock); 112 113 return ret >= 0 ? 0 : ret; 114 } 115 116 /** 117 * sht21_show_temperature() - show temperature measurement value in sysfs 118 * @dev: device 119 * @attr: device attribute 120 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to 121 * 122 * Will be called on read access to temp1_input sysfs attribute. 123 * Returns number of bytes written into buffer, negative errno on error. 124 */ 125 static ssize_t sht21_temperature_show(struct device *dev, 126 struct device_attribute *attr, 127 char *buf) 128 { 129 struct sht21 *sht21 = dev_get_drvdata(dev); 130 int ret; 131 132 ret = sht21_update_measurements(dev); 133 if (ret < 0) 134 return ret; 135 return sprintf(buf, "%d\n", sht21->temperature); 136 } 137 138 /** 139 * sht21_show_humidity() - show humidity measurement value in sysfs 140 * @dev: device 141 * @attr: device attribute 142 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to 143 * 144 * Will be called on read access to humidity1_input sysfs attribute. 145 * Returns number of bytes written into buffer, negative errno on error. 146 */ 147 static ssize_t sht21_humidity_show(struct device *dev, 148 struct device_attribute *attr, char *buf) 149 { 150 struct sht21 *sht21 = dev_get_drvdata(dev); 151 int ret; 152 153 ret = sht21_update_measurements(dev); 154 if (ret < 0) 155 return ret; 156 return sprintf(buf, "%d\n", sht21->humidity); 157 } 158 159 static ssize_t eic_read(struct sht21 *sht21) 160 { 161 struct i2c_client *client = sht21->client; 162 u8 tx[2]; 163 u8 rx[8]; 164 u8 eic[8]; 165 struct i2c_msg msgs[2] = { 166 { 167 .addr = client->addr, 168 .flags = 0, 169 .len = 2, 170 .buf = tx, 171 }, 172 { 173 .addr = client->addr, 174 .flags = I2C_M_RD, 175 .len = 8, 176 .buf = rx, 177 }, 178 }; 179 int ret; 180 181 tx[0] = SHT21_READ_SNB_CMD1; 182 tx[1] = SHT21_READ_SNB_CMD2; 183 ret = i2c_transfer(client->adapter, msgs, 2); 184 if (ret < 0) 185 goto out; 186 eic[2] = rx[0]; 187 eic[3] = rx[2]; 188 eic[4] = rx[4]; 189 eic[5] = rx[6]; 190 191 tx[0] = SHT21_READ_SNAC_CMD1; 192 tx[1] = SHT21_READ_SNAC_CMD2; 193 msgs[1].len = 6; 194 ret = i2c_transfer(client->adapter, msgs, 2); 195 if (ret < 0) 196 goto out; 197 eic[0] = rx[3]; 198 eic[1] = rx[4]; 199 eic[6] = rx[0]; 200 eic[7] = rx[1]; 201 202 ret = snprintf(sht21->eic, sizeof(sht21->eic), 203 "%02x%02x%02x%02x%02x%02x%02x%02x\n", 204 eic[0], eic[1], eic[2], eic[3], 205 eic[4], eic[5], eic[6], eic[7]); 206 out: 207 if (ret < 0) 208 sht21->eic[0] = 0; 209 210 return ret; 211 } 212 213 /** 214 * eic_show() - show Electronic Identification Code in sysfs 215 * @dev: device 216 * @attr: device attribute 217 * @buf: sysfs buffer (PAGE_SIZE) where EIC is written 218 * 219 * Will be called on read access to eic sysfs attribute. 220 * Returns number of bytes written into buffer, negative errno on error. 221 */ 222 static ssize_t eic_show(struct device *dev, 223 struct device_attribute *attr, 224 char *buf) 225 { 226 struct sht21 *sht21 = dev_get_drvdata(dev); 227 int ret; 228 229 ret = sizeof(sht21->eic) - 1; 230 mutex_lock(&sht21->lock); 231 if (!sht21->eic[0]) 232 ret = eic_read(sht21); 233 if (ret > 0) 234 memcpy(buf, sht21->eic, ret); 235 mutex_unlock(&sht21->lock); 236 return ret; 237 } 238 239 /* sysfs attributes */ 240 static SENSOR_DEVICE_ATTR_RO(temp1_input, sht21_temperature, 0); 241 static SENSOR_DEVICE_ATTR_RO(humidity1_input, sht21_humidity, 0); 242 static DEVICE_ATTR_RO(eic); 243 244 static struct attribute *sht21_attrs[] = { 245 &sensor_dev_attr_temp1_input.dev_attr.attr, 246 &sensor_dev_attr_humidity1_input.dev_attr.attr, 247 &dev_attr_eic.attr, 248 NULL 249 }; 250 251 ATTRIBUTE_GROUPS(sht21); 252 253 static int sht21_probe(struct i2c_client *client) 254 { 255 struct device *dev = &client->dev; 256 struct device *hwmon_dev; 257 struct sht21 *sht21; 258 259 if (!i2c_check_functionality(client->adapter, 260 I2C_FUNC_SMBUS_WORD_DATA)) { 261 dev_err(&client->dev, 262 "adapter does not support SMBus word transactions\n"); 263 return -ENODEV; 264 } 265 266 sht21 = devm_kzalloc(dev, sizeof(*sht21), GFP_KERNEL); 267 if (!sht21) 268 return -ENOMEM; 269 270 sht21->client = client; 271 272 mutex_init(&sht21->lock); 273 274 hwmon_dev = devm_hwmon_device_register_with_groups(dev, client->name, 275 sht21, sht21_groups); 276 return PTR_ERR_OR_ZERO(hwmon_dev); 277 } 278 279 /* Device ID table */ 280 static const struct i2c_device_id sht21_id[] = { 281 { "sht21", 0 }, 282 { } 283 }; 284 MODULE_DEVICE_TABLE(i2c, sht21_id); 285 286 static struct i2c_driver sht21_driver = { 287 .driver.name = "sht21", 288 .probe_new = sht21_probe, 289 .id_table = sht21_id, 290 }; 291 292 module_i2c_driver(sht21_driver); 293 294 MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>"); 295 MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver"); 296 MODULE_LICENSE("GPL"); 297