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 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");