drivers/hwmon/sht21.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /* Sensirion SHT21 humidity and temperature sensor driver
   3  *
   4  * Copyright (C) 2010 Urs Fleisch <urs.fleisch@sensirion.com>
   5  *
   6  * Data sheet available at https://www.sensirion.com/file/datasheet_sht21
   7  */
   8
   9 #include <linux/module.h>
  10 #include <linux/init.h>
  11 #include <linux/slab.h>
  12 #include <linux/i2c.h>
  13 #include <linux/hwmon.h>
  14 #include <linux/hwmon-sysfs.h>
  15 #include <linux/err.h>
  16 #include <linux/mutex.h>
  17 #include <linux/device.h>
  18 #include <linux/jiffies.h>
  19
  20 /* I2C command bytes */
  21 #define SHT21_TRIG_T_MEASUREMENT_HM  0xe3
  22 #define SHT21_TRIG_RH_MEASUREMENT_HM 0xe5
  23 #define SHT21_READ_SNB_CMD1 0xFA
  24 #define SHT21_READ_SNB_CMD2 0x0F
  25 #define SHT21_READ_SNAC_CMD1 0xFC
  26 #define SHT21_READ_SNAC_CMD2 0xC9
  27
  28 /**
  29  * struct sht21 - SHT21 device specific data
  30  * @client: I2C client device
  31  * @lock: mutex to protect measurement values
  32  * @last_update: time of last update (jiffies)
  33  * @temperature: cached temperature measurement value
  34  * @humidity: cached humidity measurement value
  35  * @valid: only 0 before first measurement is taken
  36  * @eic: cached electronic identification code text
  37  */
  38 struct sht21 {
  39         struct i2c_client *client;
  40         struct mutex lock;
  41         unsigned long last_update;
  42         int temperature;
  43         int humidity;
  44         char valid;
  45         char eic[18];
  46 };
  47
  48 /**
  49  * sht21_temp_ticks_to_millicelsius() - convert raw temperature ticks to
  50  * milli celsius
  51  * @ticks: temperature ticks value received from sensor
  52  */
  53 static inline int sht21_temp_ticks_to_millicelsius(int ticks)
  54 {
  55         ticks &= ~0x0003; /* clear status bits */
  56         /*
  57          * Formula T = -46.85 + 175.72 * ST / 2^16 from data sheet 6.2,
  58          * optimized for integer fixed point (3 digits) arithmetic
  59          */
  60         return ((21965 * ticks) >> 13) - 46850;
  61 }
  62
  63 /**
  64  * sht21_rh_ticks_to_per_cent_mille() - convert raw humidity ticks to
  65  * one-thousandths of a percent relative humidity
  66  * @ticks: humidity ticks value received from sensor
  67  */
  68 static inline int sht21_rh_ticks_to_per_cent_mille(int ticks)
  69 {
  70         ticks &= ~0x0003; /* clear status bits */
  71         /*
  72          * Formula RH = -6 + 125 * SRH / 2^16 from data sheet 6.1,
  73          * optimized for integer fixed point (3 digits) arithmetic
  74          */
  75         return ((15625 * ticks) >> 13) - 6000;
  76 }
  77
  78 /**
  79  * sht21_update_measurements() - get updated measurements from device
  80  * @dev: device
  81  *
  82  * Returns 0 on success, else negative errno.
  83  */
  84 static int sht21_update_measurements(struct device *dev)
  85 {
  86         int ret = 0;
  87         struct sht21 *sht21 = dev_get_drvdata(dev);
  88         struct i2c_client *client = sht21->client;
  89
  90         mutex_lock(&sht21->lock);
  91         /*
  92          * Data sheet 2.4:
  93          * SHT2x should not be active for more than 10% of the time - e.g.
  94          * maximum two measurements per second at 12bit accuracy shall be made.
  95          */
  96         if (time_after(jiffies, sht21->last_update + HZ / 2) || !sht21->valid) {
  97                 ret = i2c_smbus_read_word_swapped(client,
  98                                                   SHT21_TRIG_T_MEASUREMENT_HM);
  99                 if (ret < 0)
 100                         goto out;
 101                 sht21->temperature = sht21_temp_ticks_to_millicelsius(ret);
 102                 ret = i2c_smbus_read_word_swapped(client,
 103                                                   SHT21_TRIG_RH_MEASUREMENT_HM);
 104                 if (ret < 0)
 105                         goto out;
 106                 sht21->humidity = sht21_rh_ticks_to_per_cent_mille(ret);
 107                 sht21->last_update = jiffies;
 108                 sht21->valid = 1;
 109         }
 110 out:
 111         mutex_unlock(&sht21->lock);
 112
 113         return ret >= 0 ? 0 : ret;
 114 }
 115
 116 /**
 117  * sht21_show_temperature() - show temperature measurement value in sysfs
 118  * @dev: device
 119  * @attr: device attribute
 120  * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
 121  *
 122  * Will be called on read access to temp1_input sysfs attribute.
 123  * Returns number of bytes written into buffer, negative errno on error.
 124  */
 125 static ssize_t sht21_temperature_show(struct device *dev,
 126                                       struct device_attribute *attr,
 127                                       char *buf)
 128 {
 129         struct sht21 *sht21 = dev_get_drvdata(dev);
 130         int ret;
 131
 132         ret = sht21_update_measurements(dev);
 133         if (ret < 0)
 134                 return ret;
 135         return sprintf(buf, "%d\n", sht21->temperature);
 136 }
 137
 138 /**
 139  * sht21_show_humidity() - show humidity measurement value in sysfs
 140  * @dev: device
 141  * @attr: device attribute
 142  * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
 143  *
 144  * Will be called on read access to humidity1_input sysfs attribute.
 145  * Returns number of bytes written into buffer, negative errno on error.
 146  */
 147 static ssize_t sht21_humidity_show(struct device *dev,
 148                                    struct device_attribute *attr, char *buf)
 149 {
 150         struct sht21 *sht21 = dev_get_drvdata(dev);
 151         int ret;
 152
 153         ret = sht21_update_measurements(dev);
 154         if (ret < 0)
 155                 return ret;
 156         return sprintf(buf, "%d\n", sht21->humidity);
 157 }
 158
 159 static ssize_t eic_read(struct sht21 *sht21)
 160 {
 161         struct i2c_client *client = sht21->client;
 162         u8 tx[2];
 163         u8 rx[8];
 164         u8 eic[8];
 165         struct i2c_msg msgs[2] = {
 166                 {
 167                         .addr = client->addr,
 168                         .flags = 0,
 169                         .len = 2,
 170                         .buf = tx,
 171                 },
 172                 {
 173                         .addr = client->addr,
 174                         .flags = I2C_M_RD,
 175                         .len = 8,
 176                         .buf = rx,
 177                 },
 178         };
 179         int ret;
 180
 181         tx[0] = SHT21_READ_SNB_CMD1;
 182         tx[1] = SHT21_READ_SNB_CMD2;
 183         ret = i2c_transfer(client->adapter, msgs, 2);
 184         if (ret < 0)
 185                 goto out;
 186         eic[2] = rx[0];
 187         eic[3] = rx[2];
 188         eic[4] = rx[4];
 189         eic[5] = rx[6];
 190
 191         tx[0] = SHT21_READ_SNAC_CMD1;
 192         tx[1] = SHT21_READ_SNAC_CMD2;
 193         msgs[1].len = 6;
 194         ret = i2c_transfer(client->adapter, msgs, 2);
 195         if (ret < 0)
 196                 goto out;
 197         eic[0] = rx[3];
 198         eic[1] = rx[4];
 199         eic[6] = rx[0];
 200         eic[7] = rx[1];
 201
 202         ret = snprintf(sht21->eic, sizeof(sht21->eic),
 203                        "%02x%02x%02x%02x%02x%02x%02x%02x\n",
 204                        eic[0], eic[1], eic[2], eic[3],
 205                        eic[4], eic[5], eic[6], eic[7]);
 206 out:
 207         if (ret < 0)
 208                 sht21->eic[0] = 0;
 209
 210         return ret;
 211 }
 212
 213 /**
 214  * eic_show() - show Electronic Identification Code in sysfs
 215  * @dev: device
 216  * @attr: device attribute
 217  * @buf: sysfs buffer (PAGE_SIZE) where EIC is written
 218  *
 219  * Will be called on read access to eic sysfs attribute.
 220  * Returns number of bytes written into buffer, negative errno on error.
 221  */
 222 static ssize_t eic_show(struct device *dev,
 223         struct device_attribute *attr,
 224         char *buf)
 225 {
 226         struct sht21 *sht21 = dev_get_drvdata(dev);
 227         int ret;
 228
 229         ret = sizeof(sht21->eic) - 1;
 230         mutex_lock(&sht21->lock);
 231         if (!sht21->eic[0])
 232                 ret = eic_read(sht21);
 233         if (ret > 0)
 234                 memcpy(buf, sht21->eic, ret);
 235         mutex_unlock(&sht21->lock);
 236         return ret;
 237 }
 238
 239 /* sysfs attributes */
 240 static SENSOR_DEVICE_ATTR_RO(temp1_input, sht21_temperature, 0);
 241 static SENSOR_DEVICE_ATTR_RO(humidity1_input, sht21_humidity, 0);
 242 static DEVICE_ATTR_RO(eic);
 243
 244 static struct attribute *sht21_attrs[] = {
 245         &sensor_dev_attr_temp1_input.dev_attr.attr,
 246         &sensor_dev_attr_humidity1_input.dev_attr.attr,
 247         &dev_attr_eic.attr,
 248         NULL
 249 };
 250
 251 ATTRIBUTE_GROUPS(sht21);
 252
 253 static int sht21_probe(struct i2c_client *client)
 254 {
 255         struct device *dev = &client->dev;
 256         struct device *hwmon_dev;
 257         struct sht21 *sht21;
 258
 259         if (!i2c_check_functionality(client->adapter,
 260                                      I2C_FUNC_SMBUS_WORD_DATA)) {
 261                 dev_err(&client->dev,
 262                         "adapter does not support SMBus word transactions\n");
 263                 return -ENODEV;
 264         }
 265
 266         sht21 = devm_kzalloc(dev, sizeof(*sht21), GFP_KERNEL);
 267         if (!sht21)
 268                 return -ENOMEM;
 269
 270         sht21->client = client;
 271
 272         mutex_init(&sht21->lock);
 273
 274         hwmon_dev = devm_hwmon_device_register_with_groups(dev, client->name,
 275                                                            sht21, sht21_groups);
 276         return PTR_ERR_OR_ZERO(hwmon_dev);
 277 }
 278
 279 /* Device ID table */
 280 static const struct i2c_device_id sht21_id[] = {
 281         { "sht21", 0 },
 282         { }
 283 };
 284 MODULE_DEVICE_TABLE(i2c, sht21_id);
 285
 286 static struct i2c_driver sht21_driver = {
 287         .driver.name = "sht21",
 288         .probe_new   = sht21_probe,
 289         .id_table    = sht21_id,
 290 };
 291
 292 module_i2c_driver(sht21_driver);
 293
 294 MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>");
 295 MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver");
 296 MODULE_LICENSE("GPL");