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 33 /* I2C command bytes */ 34 #define SHT21_TRIG_T_MEASUREMENT_HM 0xe3 35 #define SHT21_TRIG_RH_MEASUREMENT_HM 0xe5 36 37 /** 38 * struct sht21 - SHT21 device specific data 39 * @hwmon_dev: device registered with hwmon 40 * @lock: mutex to protect measurement values 41 * @valid: only 0 before first measurement is taken 42 * @last_update: time of last update (jiffies) 43 * @temperature: cached temperature measurement value 44 * @humidity: cached humidity measurement value 45 */ 46 struct sht21 { 47 struct device *hwmon_dev; 48 struct mutex lock; 49 char valid; 50 unsigned long last_update; 51 int temperature; 52 int humidity; 53 }; 54 55 /** 56 * sht21_temp_ticks_to_millicelsius() - convert raw temperature ticks to 57 * milli celsius 58 * @ticks: temperature ticks value received from sensor 59 */ 60 static inline int sht21_temp_ticks_to_millicelsius(int ticks) 61 { 62 ticks &= ~0x0003; /* clear status bits */ 63 /* 64 * Formula T = -46.85 + 175.72 * ST / 2^16 from data sheet 6.2, 65 * optimized for integer fixed point (3 digits) arithmetic 66 */ 67 return ((21965 * ticks) >> 13) - 46850; 68 } 69 70 /** 71 * sht21_rh_ticks_to_per_cent_mille() - convert raw humidity ticks to 72 * one-thousandths of a percent relative humidity 73 * @ticks: humidity ticks value received from sensor 74 */ 75 static inline int sht21_rh_ticks_to_per_cent_mille(int ticks) 76 { 77 ticks &= ~0x0003; /* clear status bits */ 78 /* 79 * Formula RH = -6 + 125 * SRH / 2^16 from data sheet 6.1, 80 * optimized for integer fixed point (3 digits) arithmetic 81 */ 82 return ((15625 * ticks) >> 13) - 6000; 83 } 84 85 /** 86 * sht21_update_measurements() - get updated measurements from device 87 * @client: I2C client device 88 * 89 * Returns 0 on success, else negative errno. 90 */ 91 static int sht21_update_measurements(struct i2c_client *client) 92 { 93 int ret = 0; 94 struct sht21 *sht21 = i2c_get_clientdata(client); 95 96 mutex_lock(&sht21->lock); 97 /* 98 * Data sheet 2.4: 99 * SHT2x should not be active for more than 10% of the time - e.g. 100 * maximum two measurements per second at 12bit accuracy shall be made. 101 */ 102 if (time_after(jiffies, sht21->last_update + HZ / 2) || !sht21->valid) { 103 ret = i2c_smbus_read_word_swapped(client, 104 SHT21_TRIG_T_MEASUREMENT_HM); 105 if (ret < 0) 106 goto out; 107 sht21->temperature = sht21_temp_ticks_to_millicelsius(ret); 108 ret = i2c_smbus_read_word_swapped(client, 109 SHT21_TRIG_RH_MEASUREMENT_HM); 110 if (ret < 0) 111 goto out; 112 sht21->humidity = sht21_rh_ticks_to_per_cent_mille(ret); 113 sht21->last_update = jiffies; 114 sht21->valid = 1; 115 } 116 out: 117 mutex_unlock(&sht21->lock); 118 119 return ret >= 0 ? 0 : ret; 120 } 121 122 /** 123 * sht21_show_temperature() - show temperature measurement value in sysfs 124 * @dev: device 125 * @attr: device attribute 126 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to 127 * 128 * Will be called on read access to temp1_input sysfs attribute. 129 * Returns number of bytes written into buffer, negative errno on error. 130 */ 131 static ssize_t sht21_show_temperature(struct device *dev, 132 struct device_attribute *attr, 133 char *buf) 134 { 135 struct i2c_client *client = to_i2c_client(dev); 136 struct sht21 *sht21 = i2c_get_clientdata(client); 137 int ret = sht21_update_measurements(client); 138 if (ret < 0) 139 return ret; 140 return sprintf(buf, "%d\n", sht21->temperature); 141 } 142 143 /** 144 * sht21_show_humidity() - show humidity measurement value in sysfs 145 * @dev: device 146 * @attr: device attribute 147 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to 148 * 149 * Will be called on read access to humidity1_input sysfs attribute. 150 * Returns number of bytes written into buffer, negative errno on error. 151 */ 152 static ssize_t sht21_show_humidity(struct device *dev, 153 struct device_attribute *attr, 154 char *buf) 155 { 156 struct i2c_client *client = to_i2c_client(dev); 157 struct sht21 *sht21 = i2c_get_clientdata(client); 158 int ret = sht21_update_measurements(client); 159 if (ret < 0) 160 return ret; 161 return sprintf(buf, "%d\n", sht21->humidity); 162 } 163 164 /* sysfs attributes */ 165 static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO, sht21_show_temperature, 166 NULL, 0); 167 static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO, sht21_show_humidity, 168 NULL, 0); 169 170 static struct attribute *sht21_attributes[] = { 171 &sensor_dev_attr_temp1_input.dev_attr.attr, 172 &sensor_dev_attr_humidity1_input.dev_attr.attr, 173 NULL 174 }; 175 176 static const struct attribute_group sht21_attr_group = { 177 .attrs = sht21_attributes, 178 }; 179 180 /** 181 * sht21_probe() - probe device 182 * @client: I2C client device 183 * @id: device ID 184 * 185 * Called by the I2C core when an entry in the ID table matches a 186 * device's name. 187 * Returns 0 on success. 188 */ 189 static int __devinit sht21_probe(struct i2c_client *client, 190 const struct i2c_device_id *id) 191 { 192 struct sht21 *sht21; 193 int err; 194 195 if (!i2c_check_functionality(client->adapter, 196 I2C_FUNC_SMBUS_WORD_DATA)) { 197 dev_err(&client->dev, 198 "adapter does not support SMBus word transactions\n"); 199 return -ENODEV; 200 } 201 202 sht21 = devm_kzalloc(&client->dev, sizeof(*sht21), GFP_KERNEL); 203 if (!sht21) 204 return -ENOMEM; 205 206 i2c_set_clientdata(client, sht21); 207 208 mutex_init(&sht21->lock); 209 210 err = sysfs_create_group(&client->dev.kobj, &sht21_attr_group); 211 if (err) { 212 dev_dbg(&client->dev, "could not create sysfs files\n"); 213 return err; 214 } 215 sht21->hwmon_dev = hwmon_device_register(&client->dev); 216 if (IS_ERR(sht21->hwmon_dev)) { 217 dev_dbg(&client->dev, "unable to register hwmon device\n"); 218 err = PTR_ERR(sht21->hwmon_dev); 219 goto fail_remove_sysfs; 220 } 221 222 dev_info(&client->dev, "initialized\n"); 223 224 return 0; 225 226 fail_remove_sysfs: 227 sysfs_remove_group(&client->dev.kobj, &sht21_attr_group); 228 return err; 229 } 230 231 /** 232 * sht21_remove() - remove device 233 * @client: I2C client device 234 */ 235 static int __devexit sht21_remove(struct i2c_client *client) 236 { 237 struct sht21 *sht21 = i2c_get_clientdata(client); 238 239 hwmon_device_unregister(sht21->hwmon_dev); 240 sysfs_remove_group(&client->dev.kobj, &sht21_attr_group); 241 242 return 0; 243 } 244 245 /* Device ID table */ 246 static const struct i2c_device_id sht21_id[] = { 247 { "sht21", 0 }, 248 { } 249 }; 250 MODULE_DEVICE_TABLE(i2c, sht21_id); 251 252 static struct i2c_driver sht21_driver = { 253 .driver.name = "sht21", 254 .probe = sht21_probe, 255 .remove = __devexit_p(sht21_remove), 256 .id_table = sht21_id, 257 }; 258 259 module_i2c_driver(sht21_driver); 260 261 MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>"); 262 MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver"); 263 MODULE_LICENSE("GPL"); 264