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 #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
  38 /**
  39  * struct sht21 - SHT21 device specific data
  40  * @hwmon_dev: device registered with hwmon
  41  * @lock: mutex to protect measurement values
  42  * @valid: only 0 before first measurement is taken
  43  * @last_update: time of last update (jiffies)
  44  * @temperature: cached temperature measurement value
  45  * @humidity: cached humidity measurement value
  46  */
  47 struct sht21 {
  48         struct device *hwmon_dev;
  49         struct mutex lock;
  50         char valid;
  51         unsigned long last_update;
  52         int temperature;
  53         int humidity;
  54 };
  55
  56 /**
  57  * sht21_temp_ticks_to_millicelsius() - convert raw temperature ticks to
  58  * milli celsius
  59  * @ticks: temperature ticks value received from sensor
  60  */
  61 static inline int sht21_temp_ticks_to_millicelsius(int ticks)
  62 {
  63         ticks &= ~0x0003; /* clear status bits */
  64         /*
  65          * Formula T = -46.85 + 175.72 * ST / 2^16 from data sheet 6.2,
  66          * optimized for integer fixed point (3 digits) arithmetic
  67          */
  68         return ((21965 * ticks) >> 13) - 46850;
  69 }
  70
  71 /**
  72  * sht21_rh_ticks_to_per_cent_mille() - convert raw humidity ticks to
  73  * one-thousandths of a percent relative humidity
  74  * @ticks: humidity ticks value received from sensor
  75  */
  76 static inline int sht21_rh_ticks_to_per_cent_mille(int ticks)
  77 {
  78         ticks &= ~0x0003; /* clear status bits */
  79         /*
  80          * Formula RH = -6 + 125 * SRH / 2^16 from data sheet 6.1,
  81          * optimized for integer fixed point (3 digits) arithmetic
  82          */
  83         return ((15625 * ticks) >> 13) - 6000;
  84 }
  85
  86 /**
  87  * sht21_update_measurements() - get updated measurements from device
  88  * @client: I2C client device
  89  *
  90  * Returns 0 on success, else negative errno.
  91  */
  92 static int sht21_update_measurements(struct i2c_client *client)
  93 {
  94         int ret = 0;
  95         struct sht21 *sht21 = i2c_get_clientdata(client);
  96
  97         mutex_lock(&sht21->lock);
  98         /*
  99          * Data sheet 2.4:
 100          * SHT2x should not be active for more than 10% of the time - e.g.
 101          * maximum two measurements per second at 12bit accuracy shall be made.
 102          */
 103         if (time_after(jiffies, sht21->last_update + HZ / 2) || !sht21->valid) {
 104                 ret = i2c_smbus_read_word_swapped(client,
 105                                                   SHT21_TRIG_T_MEASUREMENT_HM);
 106                 if (ret < 0)
 107                         goto out;
 108                 sht21->temperature = sht21_temp_ticks_to_millicelsius(ret);
 109                 ret = i2c_smbus_read_word_swapped(client,
 110                                                   SHT21_TRIG_RH_MEASUREMENT_HM);
 111                 if (ret < 0)
 112                         goto out;
 113                 sht21->humidity = sht21_rh_ticks_to_per_cent_mille(ret);
 114                 sht21->last_update = jiffies;
 115                 sht21->valid = 1;
 116         }
 117 out:
 118         mutex_unlock(&sht21->lock);
 119
 120         return ret >= 0 ? 0 : ret;
 121 }
 122
 123 /**
 124  * sht21_show_temperature() - show temperature measurement value in sysfs
 125  * @dev: device
 126  * @attr: device attribute
 127  * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
 128  *
 129  * Will be called on read access to temp1_input sysfs attribute.
 130  * Returns number of bytes written into buffer, negative errno on error.
 131  */
 132 static ssize_t sht21_show_temperature(struct device *dev,
 133         struct device_attribute *attr,
 134         char *buf)
 135 {
 136         struct i2c_client *client = to_i2c_client(dev);
 137         struct sht21 *sht21 = i2c_get_clientdata(client);
 138         int ret = sht21_update_measurements(client);
 139         if (ret < 0)
 140                 return ret;
 141         return sprintf(buf, "%d\n", sht21->temperature);
 142 }
 143
 144 /**
 145  * sht21_show_humidity() - show humidity measurement value in sysfs
 146  * @dev: device
 147  * @attr: device attribute
 148  * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
 149  *
 150  * Will be called on read access to humidity1_input sysfs attribute.
 151  * Returns number of bytes written into buffer, negative errno on error.
 152  */
 153 static ssize_t sht21_show_humidity(struct device *dev,
 154         struct device_attribute *attr,
 155         char *buf)
 156 {
 157         struct i2c_client *client = to_i2c_client(dev);
 158         struct sht21 *sht21 = i2c_get_clientdata(client);
 159         int ret = sht21_update_measurements(client);
 160         if (ret < 0)
 161                 return ret;
 162         return sprintf(buf, "%d\n", sht21->humidity);
 163 }
 164
 165 /* sysfs attributes */
 166 static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO, sht21_show_temperature,
 167         NULL, 0);
 168 static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO, sht21_show_humidity,
 169         NULL, 0);
 170
 171 static struct attribute *sht21_attributes[] = {
 172         &sensor_dev_attr_temp1_input.dev_attr.attr,
 173         &sensor_dev_attr_humidity1_input.dev_attr.attr,
 174         NULL
 175 };
 176
 177 static const struct attribute_group sht21_attr_group = {
 178         .attrs = sht21_attributes,
 179 };
 180
 181 /**
 182  * sht21_probe() - probe device
 183  * @client: I2C client device
 184  * @id: device ID
 185  *
 186  * Called by the I2C core when an entry in the ID table matches a
 187  * device's name.
 188  * Returns 0 on success.
 189  */
 190 static int __devinit sht21_probe(struct i2c_client *client,
 191         const struct i2c_device_id *id)
 192 {
 193         struct sht21 *sht21;
 194         int err;
 195
 196         if (!i2c_check_functionality(client->adapter,
 197                                      I2C_FUNC_SMBUS_WORD_DATA)) {
 198                 dev_err(&client->dev,
 199                         "adapter does not support SMBus word transactions\n");
 200                 return -ENODEV;
 201         }
 202
 203         sht21 = devm_kzalloc(&client->dev, sizeof(*sht21), GFP_KERNEL);
 204         if (!sht21)
 205                 return -ENOMEM;
 206
 207         i2c_set_clientdata(client, sht21);
 208
 209         mutex_init(&sht21->lock);
 210
 211         err = sysfs_create_group(&client->dev.kobj, &sht21_attr_group);
 212         if (err) {
 213                 dev_dbg(&client->dev, "could not create sysfs files\n");
 214                 return err;
 215         }
 216         sht21->hwmon_dev = hwmon_device_register(&client->dev);
 217         if (IS_ERR(sht21->hwmon_dev)) {
 218                 dev_dbg(&client->dev, "unable to register hwmon device\n");
 219                 err = PTR_ERR(sht21->hwmon_dev);
 220                 goto fail_remove_sysfs;
 221         }
 222
 223         dev_info(&client->dev, "initialized\n");
 224
 225         return 0;
 226
 227 fail_remove_sysfs:
 228         sysfs_remove_group(&client->dev.kobj, &sht21_attr_group);
 229         return err;
 230 }
 231
 232 /**
 233  * sht21_remove() - remove device
 234  * @client: I2C client device
 235  */
 236 static int __devexit sht21_remove(struct i2c_client *client)
 237 {
 238         struct sht21 *sht21 = i2c_get_clientdata(client);
 239
 240         hwmon_device_unregister(sht21->hwmon_dev);
 241         sysfs_remove_group(&client->dev.kobj, &sht21_attr_group);
 242
 243         return 0;
 244 }
 245
 246 /* Device ID table */
 247 static const struct i2c_device_id sht21_id[] = {
 248         { "sht21", 0 },
 249         { }
 250 };
 251 MODULE_DEVICE_TABLE(i2c, sht21_id);
 252
 253 static struct i2c_driver sht21_driver = {
 254         .driver.name = "sht21",
 255         .probe       = sht21_probe,
 256         .remove      = __devexit_p(sht21_remove),
 257         .id_table    = sht21_id,
 258 };
 259
 260 module_i2c_driver(sht21_driver);
 261
 262 MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>");
 263 MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver");
 264 MODULE_LICENSE("GPL");