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 33 /* I2C command bytes */ 34 #define SHT21_TRIG_T_MEASUREMENT_HM 0xe3 35 #define SHT21_TRIG_RH_MEASUREMENT_HM 0xe5 36 37 /** 38 * struct sht21 - SHT21 device specific data 39 * @hwmon_dev: device registered with hwmon 40 * @lock: mutex to protect measurement values 41 * @valid: only 0 before first measurement is taken 42 * @last_update: time of last update (jiffies) 43 * @temperature: cached temperature measurement value 44 * @humidity: cached humidity measurement value 45 */ 46 struct sht21 { 47 struct device *hwmon_dev; 48 struct mutex lock; 49 char valid; 50 unsigned long last_update; 51 int temperature; 52 int humidity; 53 }; 54 55 /** 56 * sht21_temp_ticks_to_millicelsius() - convert raw temperature ticks to 57 * milli celsius 58 * @ticks: temperature ticks value received from sensor 59 */ 60 static inline int sht21_temp_ticks_to_millicelsius(int ticks) 61 { 62 ticks &= ~0x0003; /* clear status bits */ 63 /* 64 * Formula T = -46.85 + 175.72 * ST / 2^16 from data sheet 6.2, 65 * optimized for integer fixed point (3 digits) arithmetic 66 */ 67 return ((21965 * ticks) >> 13) - 46850; 68 } 69 70 /** 71 * sht21_rh_ticks_to_per_cent_mille() - convert raw humidity ticks to 72 * one-thousandths of a percent relative humidity 73 * @ticks: humidity ticks value received from sensor 74 */ 75 static inline int sht21_rh_ticks_to_per_cent_mille(int ticks) 76 { 77 ticks &= ~0x0003; /* clear status bits */ 78 /* 79 * Formula RH = -6 + 125 * SRH / 2^16 from data sheet 6.1, 80 * optimized for integer fixed point (3 digits) arithmetic 81 */ 82 return ((15625 * ticks) >> 13) - 6000; 83 } 84 85 /** 86 * sht21_read_word_data() - read word from register 87 * @client: I2C client device 88 * @reg: I2C command byte 89 * 90 * Returns value, negative errno on error. 91 */ 92 static inline int sht21_read_word_data(struct i2c_client *client, u8 reg) 93 { 94 int ret = i2c_smbus_read_word_data(client, reg); 95 if (ret < 0) 96 return ret; 97 /* 98 * SMBus specifies low byte first, but the SHT21 returns MSB 99 * first, so we have to swab16 the values 100 */ 101 return swab16(ret); 102 } 103 104 /** 105 * sht21_update_measurements() - get updated measurements from device 106 * @client: I2C client device 107 * 108 * Returns 0 on success, else negative errno. 109 */ 110 static int sht21_update_measurements(struct i2c_client *client) 111 { 112 int ret = 0; 113 struct sht21 *sht21 = i2c_get_clientdata(client); 114 115 mutex_lock(&sht21->lock); 116 /* 117 * Data sheet 2.4: 118 * SHT2x should not be active for more than 10% of the time - e.g. 119 * maximum two measurements per second at 12bit accuracy shall be made. 120 */ 121 if (time_after(jiffies, sht21->last_update + HZ / 2) || !sht21->valid) { 122 ret = sht21_read_word_data(client, SHT21_TRIG_T_MEASUREMENT_HM); 123 if (ret < 0) 124 goto out; 125 sht21->temperature = sht21_temp_ticks_to_millicelsius(ret); 126 ret = sht21_read_word_data(client, 127 SHT21_TRIG_RH_MEASUREMENT_HM); 128 if (ret < 0) 129 goto out; 130 sht21->humidity = sht21_rh_ticks_to_per_cent_mille(ret); 131 sht21->last_update = jiffies; 132 sht21->valid = 1; 133 } 134 out: 135 mutex_unlock(&sht21->lock); 136 137 return ret >= 0 ? 0 : ret; 138 } 139 140 /** 141 * sht21_show_temperature() - show temperature measurement value in sysfs 142 * @dev: device 143 * @attr: device attribute 144 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to 145 * 146 * Will be called on read access to temp1_input sysfs attribute. 147 * Returns number of bytes written into buffer, negative errno on error. 148 */ 149 static ssize_t sht21_show_temperature(struct device *dev, 150 struct device_attribute *attr, 151 char *buf) 152 { 153 struct i2c_client *client = to_i2c_client(dev); 154 struct sht21 *sht21 = i2c_get_clientdata(client); 155 int ret = sht21_update_measurements(client); 156 if (ret < 0) 157 return ret; 158 return sprintf(buf, "%d\n", sht21->temperature); 159 } 160 161 /** 162 * sht21_show_humidity() - show humidity measurement value in sysfs 163 * @dev: device 164 * @attr: device attribute 165 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to 166 * 167 * Will be called on read access to humidity1_input sysfs attribute. 168 * Returns number of bytes written into buffer, negative errno on error. 169 */ 170 static ssize_t sht21_show_humidity(struct device *dev, 171 struct device_attribute *attr, 172 char *buf) 173 { 174 struct i2c_client *client = to_i2c_client(dev); 175 struct sht21 *sht21 = i2c_get_clientdata(client); 176 int ret = sht21_update_measurements(client); 177 if (ret < 0) 178 return ret; 179 return sprintf(buf, "%d\n", sht21->humidity); 180 } 181 182 /* sysfs attributes */ 183 static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO, sht21_show_temperature, 184 NULL, 0); 185 static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO, sht21_show_humidity, 186 NULL, 0); 187 188 static struct attribute *sht21_attributes[] = { 189 &sensor_dev_attr_temp1_input.dev_attr.attr, 190 &sensor_dev_attr_humidity1_input.dev_attr.attr, 191 NULL 192 }; 193 194 static const struct attribute_group sht21_attr_group = { 195 .attrs = sht21_attributes, 196 }; 197 198 /** 199 * sht21_probe() - probe device 200 * @client: I2C client device 201 * @id: device ID 202 * 203 * Called by the I2C core when an entry in the ID table matches a 204 * device's name. 205 * Returns 0 on success. 206 */ 207 static int __devinit sht21_probe(struct i2c_client *client, 208 const struct i2c_device_id *id) 209 { 210 struct sht21 *sht21; 211 int err; 212 213 if (!i2c_check_functionality(client->adapter, 214 I2C_FUNC_SMBUS_WORD_DATA)) { 215 dev_err(&client->dev, 216 "adapter does not support SMBus word transactions\n"); 217 return -ENODEV; 218 } 219 220 sht21 = kzalloc(sizeof(*sht21), GFP_KERNEL); 221 if (!sht21) { 222 dev_dbg(&client->dev, "kzalloc failed\n"); 223 return -ENOMEM; 224 } 225 i2c_set_clientdata(client, sht21); 226 227 mutex_init(&sht21->lock); 228 229 err = sysfs_create_group(&client->dev.kobj, &sht21_attr_group); 230 if (err) { 231 dev_dbg(&client->dev, "could not create sysfs files\n"); 232 goto fail_free; 233 } 234 sht21->hwmon_dev = hwmon_device_register(&client->dev); 235 if (IS_ERR(sht21->hwmon_dev)) { 236 dev_dbg(&client->dev, "unable to register hwmon device\n"); 237 err = PTR_ERR(sht21->hwmon_dev); 238 goto fail_remove_sysfs; 239 } 240 241 dev_info(&client->dev, "initialized\n"); 242 243 return 0; 244 245 fail_remove_sysfs: 246 sysfs_remove_group(&client->dev.kobj, &sht21_attr_group); 247 fail_free: 248 kfree(sht21); 249 250 return err; 251 } 252 253 /** 254 * sht21_remove() - remove device 255 * @client: I2C client device 256 */ 257 static int __devexit sht21_remove(struct i2c_client *client) 258 { 259 struct sht21 *sht21 = i2c_get_clientdata(client); 260 261 hwmon_device_unregister(sht21->hwmon_dev); 262 sysfs_remove_group(&client->dev.kobj, &sht21_attr_group); 263 kfree(sht21); 264 265 return 0; 266 } 267 268 /* Device ID table */ 269 static const struct i2c_device_id sht21_id[] = { 270 { "sht21", 0 }, 271 { } 272 }; 273 MODULE_DEVICE_TABLE(i2c, sht21_id); 274 275 static struct i2c_driver sht21_driver = { 276 .driver.name = "sht21", 277 .probe = sht21_probe, 278 .remove = __devexit_p(sht21_remove), 279 .id_table = sht21_id, 280 }; 281 282 /** 283 * sht21_init() - initialize driver 284 * 285 * Called when kernel is booted or module is inserted. 286 * Returns 0 on success. 287 */ 288 static int __init sht21_init(void) 289 { 290 return i2c_add_driver(&sht21_driver); 291 } 292 module_init(sht21_init); 293 294 /** 295 * sht21_init() - clean up driver 296 * 297 * Called when module is removed. 298 */ 299 static void __exit sht21_exit(void) 300 { 301 i2c_del_driver(&sht21_driver); 302 } 303 module_exit(sht21_exit); 304 305 MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>"); 306 MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver"); 307 MODULE_LICENSE("GPL"); 308