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