1 /* Sensirion SHT21 humidity and temperature sensor driver 2 * 3 * Copyright (C) 2010 Urs Fleisch <urs.fleisch@sensirion.com> 4 * 5 * This program is free software; you can redistribute it and/or modify 6 * it under the terms of the GNU General Public License as published by 7 * the Free Software Foundation; either version 2 of the License, or 8 * (at your option) any later version. 9 * 10 * This program is distributed in the hope that it will be useful, 11 * but WITHOUT ANY WARRANTY; without even the implied warranty of 12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 13 * GNU General Public License for more details. 14 * 15 * You should have received a copy of the GNU General Public License 16 * along with this program; if not, write to the Free Software 17 * Foundation, Inc., 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA 18 * 19 * Data sheet available (5/2010) at 20 * http://www.sensirion.com/en/pdf/product_information/Datasheet-humidity-sensor-SHT21.pdf 21 */ 22 23 #include <linux/module.h> 24 #include <linux/init.h> 25 #include <linux/slab.h> 26 #include <linux/i2c.h> 27 #include <linux/hwmon.h> 28 #include <linux/hwmon-sysfs.h> 29 #include <linux/err.h> 30 #include <linux/mutex.h> 31 #include <linux/device.h> 32 #include <linux/jiffies.h> 33 34 /* I2C command bytes */ 35 #define SHT21_TRIG_T_MEASUREMENT_HM 0xe3 36 #define SHT21_TRIG_RH_MEASUREMENT_HM 0xe5 37 #define SHT21_READ_SNB_CMD1 0xFA 38 #define SHT21_READ_SNB_CMD2 0x0F 39 #define SHT21_READ_SNAC_CMD1 0xFC 40 #define SHT21_READ_SNAC_CMD2 0xC9 41 42 /** 43 * struct sht21 - SHT21 device specific data 44 * @hwmon_dev: device registered with hwmon 45 * @lock: mutex to protect measurement values 46 * @last_update: time of last update (jiffies) 47 * @temperature: cached temperature measurement value 48 * @humidity: cached humidity measurement value 49 * @valid: only 0 before first measurement is taken 50 * @eic: cached electronic identification code text 51 */ 52 struct sht21 { 53 struct i2c_client *client; 54 struct mutex lock; 55 unsigned long last_update; 56 int temperature; 57 int humidity; 58 char valid; 59 char eic[18]; 60 }; 61 62 /** 63 * sht21_temp_ticks_to_millicelsius() - convert raw temperature ticks to 64 * milli celsius 65 * @ticks: temperature ticks value received from sensor 66 */ 67 static inline int sht21_temp_ticks_to_millicelsius(int ticks) 68 { 69 ticks &= ~0x0003; /* clear status bits */ 70 /* 71 * Formula T = -46.85 + 175.72 * ST / 2^16 from data sheet 6.2, 72 * optimized for integer fixed point (3 digits) arithmetic 73 */ 74 return ((21965 * ticks) >> 13) - 46850; 75 } 76 77 /** 78 * sht21_rh_ticks_to_per_cent_mille() - convert raw humidity ticks to 79 * one-thousandths of a percent relative humidity 80 * @ticks: humidity ticks value received from sensor 81 */ 82 static inline int sht21_rh_ticks_to_per_cent_mille(int ticks) 83 { 84 ticks &= ~0x0003; /* clear status bits */ 85 /* 86 * Formula RH = -6 + 125 * SRH / 2^16 from data sheet 6.1, 87 * optimized for integer fixed point (3 digits) arithmetic 88 */ 89 return ((15625 * ticks) >> 13) - 6000; 90 } 91 92 /** 93 * sht21_update_measurements() - get updated measurements from device 94 * @dev: device 95 * 96 * Returns 0 on success, else negative errno. 97 */ 98 static int sht21_update_measurements(struct device *dev) 99 { 100 int ret = 0; 101 struct sht21 *sht21 = dev_get_drvdata(dev); 102 struct i2c_client *client = sht21->client; 103 104 mutex_lock(&sht21->lock); 105 /* 106 * Data sheet 2.4: 107 * SHT2x should not be active for more than 10% of the time - e.g. 108 * maximum two measurements per second at 12bit accuracy shall be made. 109 */ 110 if (time_after(jiffies, sht21->last_update + HZ / 2) || !sht21->valid) { 111 ret = i2c_smbus_read_word_swapped(client, 112 SHT21_TRIG_T_MEASUREMENT_HM); 113 if (ret < 0) 114 goto out; 115 sht21->temperature = sht21_temp_ticks_to_millicelsius(ret); 116 ret = i2c_smbus_read_word_swapped(client, 117 SHT21_TRIG_RH_MEASUREMENT_HM); 118 if (ret < 0) 119 goto out; 120 sht21->humidity = sht21_rh_ticks_to_per_cent_mille(ret); 121 sht21->last_update = jiffies; 122 sht21->valid = 1; 123 } 124 out: 125 mutex_unlock(&sht21->lock); 126 127 return ret >= 0 ? 0 : ret; 128 } 129 130 /** 131 * sht21_show_temperature() - show temperature measurement value in sysfs 132 * @dev: device 133 * @attr: device attribute 134 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to 135 * 136 * Will be called on read access to temp1_input sysfs attribute. 137 * Returns number of bytes written into buffer, negative errno on error. 138 */ 139 static ssize_t sht21_show_temperature(struct device *dev, 140 struct device_attribute *attr, 141 char *buf) 142 { 143 struct sht21 *sht21 = dev_get_drvdata(dev); 144 int ret; 145 146 ret = sht21_update_measurements(dev); 147 if (ret < 0) 148 return ret; 149 return sprintf(buf, "%d\n", sht21->temperature); 150 } 151 152 /** 153 * sht21_show_humidity() - show humidity measurement value in sysfs 154 * @dev: device 155 * @attr: device attribute 156 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to 157 * 158 * Will be called on read access to humidity1_input sysfs attribute. 159 * Returns number of bytes written into buffer, negative errno on error. 160 */ 161 static ssize_t sht21_show_humidity(struct device *dev, 162 struct device_attribute *attr, 163 char *buf) 164 { 165 struct sht21 *sht21 = dev_get_drvdata(dev); 166 int ret; 167 168 ret = sht21_update_measurements(dev); 169 if (ret < 0) 170 return ret; 171 return sprintf(buf, "%d\n", sht21->humidity); 172 } 173 174 static ssize_t eic_read(struct sht21 *sht21) 175 { 176 struct i2c_client *client = sht21->client; 177 u8 tx[2]; 178 u8 rx[8]; 179 u8 eic[8]; 180 struct i2c_msg msgs[2] = { 181 { 182 .addr = client->addr, 183 .flags = 0, 184 .len = 2, 185 .buf = tx, 186 }, 187 { 188 .addr = client->addr, 189 .flags = I2C_M_RD, 190 .len = 8, 191 .buf = rx, 192 }, 193 }; 194 int ret; 195 196 tx[0] = SHT21_READ_SNB_CMD1; 197 tx[1] = SHT21_READ_SNB_CMD2; 198 ret = i2c_transfer(client->adapter, msgs, 2); 199 if (ret < 0) 200 goto out; 201 eic[2] = rx[0]; 202 eic[3] = rx[2]; 203 eic[4] = rx[4]; 204 eic[5] = rx[6]; 205 206 tx[0] = SHT21_READ_SNAC_CMD1; 207 tx[1] = SHT21_READ_SNAC_CMD2; 208 msgs[1].len = 6; 209 ret = i2c_transfer(client->adapter, msgs, 2); 210 if (ret < 0) 211 goto out; 212 eic[0] = rx[3]; 213 eic[1] = rx[4]; 214 eic[6] = rx[0]; 215 eic[7] = rx[1]; 216 217 ret = snprintf(sht21->eic, sizeof(sht21->eic), 218 "%02x%02x%02x%02x%02x%02x%02x%02x\n", 219 eic[0], eic[1], eic[2], eic[3], 220 eic[4], eic[5], eic[6], eic[7]); 221 out: 222 if (ret < 0) 223 sht21->eic[0] = 0; 224 225 return ret; 226 } 227 228 /** 229 * eic_show() - show Electronic Identification Code in sysfs 230 * @dev: device 231 * @attr: device attribute 232 * @buf: sysfs buffer (PAGE_SIZE) where EIC is written 233 * 234 * Will be called on read access to eic sysfs attribute. 235 * Returns number of bytes written into buffer, negative errno on error. 236 */ 237 static ssize_t eic_show(struct device *dev, 238 struct device_attribute *attr, 239 char *buf) 240 { 241 struct sht21 *sht21 = dev_get_drvdata(dev); 242 int ret; 243 244 ret = sizeof(sht21->eic) - 1; 245 mutex_lock(&sht21->lock); 246 if (!sht21->eic[0]) 247 ret = eic_read(sht21); 248 if (ret > 0) 249 memcpy(buf, sht21->eic, ret); 250 mutex_unlock(&sht21->lock); 251 return ret; 252 } 253 254 /* sysfs attributes */ 255 static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO, sht21_show_temperature, 256 NULL, 0); 257 static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO, sht21_show_humidity, 258 NULL, 0); 259 static DEVICE_ATTR_RO(eic); 260 261 static struct attribute *sht21_attrs[] = { 262 &sensor_dev_attr_temp1_input.dev_attr.attr, 263 &sensor_dev_attr_humidity1_input.dev_attr.attr, 264 &dev_attr_eic.attr, 265 NULL 266 }; 267 268 ATTRIBUTE_GROUPS(sht21); 269 270 static int sht21_probe(struct i2c_client *client, 271 const struct i2c_device_id *id) 272 { 273 struct device *dev = &client->dev; 274 struct device *hwmon_dev; 275 struct sht21 *sht21; 276 277 if (!i2c_check_functionality(client->adapter, 278 I2C_FUNC_SMBUS_WORD_DATA)) { 279 dev_err(&client->dev, 280 "adapter does not support SMBus word transactions\n"); 281 return -ENODEV; 282 } 283 284 sht21 = devm_kzalloc(dev, sizeof(*sht21), GFP_KERNEL); 285 if (!sht21) 286 return -ENOMEM; 287 288 sht21->client = client; 289 290 mutex_init(&sht21->lock); 291 292 hwmon_dev = devm_hwmon_device_register_with_groups(dev, client->name, 293 sht21, sht21_groups); 294 return PTR_ERR_OR_ZERO(hwmon_dev); 295 } 296 297 /* Device ID table */ 298 static const struct i2c_device_id sht21_id[] = { 299 { "sht21", 0 }, 300 { } 301 }; 302 MODULE_DEVICE_TABLE(i2c, sht21_id); 303 304 static struct i2c_driver sht21_driver = { 305 .driver.name = "sht21", 306 .probe = sht21_probe, 307 .id_table = sht21_id, 308 }; 309 310 module_i2c_driver(sht21_driver); 311 312 MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>"); 313 MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver"); 314 MODULE_LICENSE("GPL"); 315