drivers/hwmon/sht21.c

   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");