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 at http://www.sensirion.com/file/datasheet_sht21 20 */ 21 22 #include <linux/module.h> 23 #include <linux/init.h> 24 #include <linux/slab.h> 25 #include <linux/i2c.h> 26 #include <linux/hwmon.h> 27 #include <linux/hwmon-sysfs.h> 28 #include <linux/err.h> 29 #include <linux/mutex.h> 30 #include <linux/device.h> 31 #include <linux/jiffies.h> 32 33 /* I2C command bytes */ 34 #define SHT21_TRIG_T_MEASUREMENT_HM 0xe3 35 #define SHT21_TRIG_RH_MEASUREMENT_HM 0xe5 36 #define SHT21_READ_SNB_CMD1 0xFA 37 #define SHT21_READ_SNB_CMD2 0x0F 38 #define SHT21_READ_SNAC_CMD1 0xFC 39 #define SHT21_READ_SNAC_CMD2 0xC9 40 41 /** 42 * struct sht21 - SHT21 device specific data 43 * @client: I2C client device 44 * @lock: mutex to protect measurement values 45 * @last_update: time of last update (jiffies) 46 * @temperature: cached temperature measurement value 47 * @humidity: cached humidity measurement value 48 * @valid: only 0 before first measurement is taken 49 * @eic: cached electronic identification code text 50 */ 51 struct sht21 { 52 struct i2c_client *client; 53 struct mutex lock; 54 unsigned long last_update; 55 int temperature; 56 int humidity; 57 char valid; 58 char eic[18]; 59 }; 60 61 /** 62 * sht21_temp_ticks_to_millicelsius() - convert raw temperature ticks to 63 * milli celsius 64 * @ticks: temperature ticks value received from sensor 65 */ 66 static inline int sht21_temp_ticks_to_millicelsius(int ticks) 67 { 68 ticks &= ~0x0003; /* clear status bits */ 69 /* 70 * Formula T = -46.85 + 175.72 * ST / 2^16 from data sheet 6.2, 71 * optimized for integer fixed point (3 digits) arithmetic 72 */ 73 return ((21965 * ticks) >> 13) - 46850; 74 } 75 76 /** 77 * sht21_rh_ticks_to_per_cent_mille() - convert raw humidity ticks to 78 * one-thousandths of a percent relative humidity 79 * @ticks: humidity ticks value received from sensor 80 */ 81 static inline int sht21_rh_ticks_to_per_cent_mille(int ticks) 82 { 83 ticks &= ~0x0003; /* clear status bits */ 84 /* 85 * Formula RH = -6 + 125 * SRH / 2^16 from data sheet 6.1, 86 * optimized for integer fixed point (3 digits) arithmetic 87 */ 88 return ((15625 * ticks) >> 13) - 6000; 89 } 90 91 /** 92 * sht21_update_measurements() - get updated measurements from device 93 * @dev: device 94 * 95 * Returns 0 on success, else negative errno. 96 */ 97 static int sht21_update_measurements(struct device *dev) 98 { 99 int ret = 0; 100 struct sht21 *sht21 = dev_get_drvdata(dev); 101 struct i2c_client *client = sht21->client; 102 103 mutex_lock(&sht21->lock); 104 /* 105 * Data sheet 2.4: 106 * SHT2x should not be active for more than 10% of the time - e.g. 107 * maximum two measurements per second at 12bit accuracy shall be made. 108 */ 109 if (time_after(jiffies, sht21->last_update + HZ / 2) || !sht21->valid) { 110 ret = i2c_smbus_read_word_swapped(client, 111 SHT21_TRIG_T_MEASUREMENT_HM); 112 if (ret < 0) 113 goto out; 114 sht21->temperature = sht21_temp_ticks_to_millicelsius(ret); 115 ret = i2c_smbus_read_word_swapped(client, 116 SHT21_TRIG_RH_MEASUREMENT_HM); 117 if (ret < 0) 118 goto out; 119 sht21->humidity = sht21_rh_ticks_to_per_cent_mille(ret); 120 sht21->last_update = jiffies; 121 sht21->valid = 1; 122 } 123 out: 124 mutex_unlock(&sht21->lock); 125 126 return ret >= 0 ? 0 : ret; 127 } 128 129 /** 130 * sht21_show_temperature() - show temperature measurement value in sysfs 131 * @dev: device 132 * @attr: device attribute 133 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to 134 * 135 * Will be called on read access to temp1_input sysfs attribute. 136 * Returns number of bytes written into buffer, negative errno on error. 137 */ 138 static ssize_t sht21_show_temperature(struct device *dev, 139 struct device_attribute *attr, 140 char *buf) 141 { 142 struct sht21 *sht21 = dev_get_drvdata(dev); 143 int ret; 144 145 ret = sht21_update_measurements(dev); 146 if (ret < 0) 147 return ret; 148 return sprintf(buf, "%d\n", sht21->temperature); 149 } 150 151 /** 152 * sht21_show_humidity() - show humidity measurement value in sysfs 153 * @dev: device 154 * @attr: device attribute 155 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to 156 * 157 * Will be called on read access to humidity1_input sysfs attribute. 158 * Returns number of bytes written into buffer, negative errno on error. 159 */ 160 static ssize_t sht21_show_humidity(struct device *dev, 161 struct device_attribute *attr, 162 char *buf) 163 { 164 struct sht21 *sht21 = dev_get_drvdata(dev); 165 int ret; 166 167 ret = sht21_update_measurements(dev); 168 if (ret < 0) 169 return ret; 170 return sprintf(buf, "%d\n", sht21->humidity); 171 } 172 173 static ssize_t eic_read(struct sht21 *sht21) 174 { 175 struct i2c_client *client = sht21->client; 176 u8 tx[2]; 177 u8 rx[8]; 178 u8 eic[8]; 179 struct i2c_msg msgs[2] = { 180 { 181 .addr = client->addr, 182 .flags = 0, 183 .len = 2, 184 .buf = tx, 185 }, 186 { 187 .addr = client->addr, 188 .flags = I2C_M_RD, 189 .len = 8, 190 .buf = rx, 191 }, 192 }; 193 int ret; 194 195 tx[0] = SHT21_READ_SNB_CMD1; 196 tx[1] = SHT21_READ_SNB_CMD2; 197 ret = i2c_transfer(client->adapter, msgs, 2); 198 if (ret < 0) 199 goto out; 200 eic[2] = rx[0]; 201 eic[3] = rx[2]; 202 eic[4] = rx[4]; 203 eic[5] = rx[6]; 204 205 tx[0] = SHT21_READ_SNAC_CMD1; 206 tx[1] = SHT21_READ_SNAC_CMD2; 207 msgs[1].len = 6; 208 ret = i2c_transfer(client->adapter, msgs, 2); 209 if (ret < 0) 210 goto out; 211 eic[0] = rx[3]; 212 eic[1] = rx[4]; 213 eic[6] = rx[0]; 214 eic[7] = rx[1]; 215 216 ret = snprintf(sht21->eic, sizeof(sht21->eic), 217 "%02x%02x%02x%02x%02x%02x%02x%02x\n", 218 eic[0], eic[1], eic[2], eic[3], 219 eic[4], eic[5], eic[6], eic[7]); 220 out: 221 if (ret < 0) 222 sht21->eic[0] = 0; 223 224 return ret; 225 } 226 227 /** 228 * eic_show() - show Electronic Identification Code in sysfs 229 * @dev: device 230 * @attr: device attribute 231 * @buf: sysfs buffer (PAGE_SIZE) where EIC is written 232 * 233 * Will be called on read access to eic sysfs attribute. 234 * Returns number of bytes written into buffer, negative errno on error. 235 */ 236 static ssize_t eic_show(struct device *dev, 237 struct device_attribute *attr, 238 char *buf) 239 { 240 struct sht21 *sht21 = dev_get_drvdata(dev); 241 int ret; 242 243 ret = sizeof(sht21->eic) - 1; 244 mutex_lock(&sht21->lock); 245 if (!sht21->eic[0]) 246 ret = eic_read(sht21); 247 if (ret > 0) 248 memcpy(buf, sht21->eic, ret); 249 mutex_unlock(&sht21->lock); 250 return ret; 251 } 252 253 /* sysfs attributes */ 254 static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO, sht21_show_temperature, 255 NULL, 0); 256 static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO, sht21_show_humidity, 257 NULL, 0); 258 static DEVICE_ATTR_RO(eic); 259 260 static struct attribute *sht21_attrs[] = { 261 &sensor_dev_attr_temp1_input.dev_attr.attr, 262 &sensor_dev_attr_humidity1_input.dev_attr.attr, 263 &dev_attr_eic.attr, 264 NULL 265 }; 266 267 ATTRIBUTE_GROUPS(sht21); 268 269 static int sht21_probe(struct i2c_client *client, 270 const struct i2c_device_id *id) 271 { 272 struct device *dev = &client->dev; 273 struct device *hwmon_dev; 274 struct sht21 *sht21; 275 276 if (!i2c_check_functionality(client->adapter, 277 I2C_FUNC_SMBUS_WORD_DATA)) { 278 dev_err(&client->dev, 279 "adapter does not support SMBus word transactions\n"); 280 return -ENODEV; 281 } 282 283 sht21 = devm_kzalloc(dev, sizeof(*sht21), GFP_KERNEL); 284 if (!sht21) 285 return -ENOMEM; 286 287 sht21->client = client; 288 289 mutex_init(&sht21->lock); 290 291 hwmon_dev = devm_hwmon_device_register_with_groups(dev, client->name, 292 sht21, sht21_groups); 293 return PTR_ERR_OR_ZERO(hwmon_dev); 294 } 295 296 /* Device ID table */ 297 static const struct i2c_device_id sht21_id[] = { 298 { "sht21", 0 }, 299 { } 300 }; 301 MODULE_DEVICE_TABLE(i2c, sht21_id); 302 303 static struct i2c_driver sht21_driver = { 304 .driver.name = "sht21", 305 .probe = sht21_probe, 306 .id_table = sht21_id, 307 }; 308 309 module_i2c_driver(sht21_driver); 310 311 MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>"); 312 MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver"); 313 MODULE_LICENSE("GPL"); 314