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 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 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 = 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"); 265