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 i2c_client *client; 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 * @dev: device 89 * 90 * Returns 0 on success, else negative errno. 91 */ 92 static int sht21_update_measurements(struct device *dev) 93 { 94 int ret = 0; 95 struct sht21 *sht21 = dev_get_drvdata(dev); 96 struct i2c_client *client = sht21->client; 97 98 mutex_lock(&sht21->lock); 99 /* 100 * Data sheet 2.4: 101 * SHT2x should not be active for more than 10% of the time - e.g. 102 * maximum two measurements per second at 12bit accuracy shall be made. 103 */ 104 if (time_after(jiffies, sht21->last_update + HZ / 2) || !sht21->valid) { 105 ret = i2c_smbus_read_word_swapped(client, 106 SHT21_TRIG_T_MEASUREMENT_HM); 107 if (ret < 0) 108 goto out; 109 sht21->temperature = sht21_temp_ticks_to_millicelsius(ret); 110 ret = i2c_smbus_read_word_swapped(client, 111 SHT21_TRIG_RH_MEASUREMENT_HM); 112 if (ret < 0) 113 goto out; 114 sht21->humidity = sht21_rh_ticks_to_per_cent_mille(ret); 115 sht21->last_update = jiffies; 116 sht21->valid = 1; 117 } 118 out: 119 mutex_unlock(&sht21->lock); 120 121 return ret >= 0 ? 0 : ret; 122 } 123 124 /** 125 * sht21_show_temperature() - show temperature measurement value in sysfs 126 * @dev: device 127 * @attr: device attribute 128 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to 129 * 130 * Will be called on read access to temp1_input sysfs attribute. 131 * Returns number of bytes written into buffer, negative errno on error. 132 */ 133 static ssize_t sht21_show_temperature(struct device *dev, 134 struct device_attribute *attr, 135 char *buf) 136 { 137 struct sht21 *sht21 = dev_get_drvdata(dev); 138 int ret; 139 140 ret = sht21_update_measurements(dev); 141 if (ret < 0) 142 return ret; 143 return sprintf(buf, "%d\n", sht21->temperature); 144 } 145 146 /** 147 * sht21_show_humidity() - show humidity measurement value in sysfs 148 * @dev: device 149 * @attr: device attribute 150 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to 151 * 152 * Will be called on read access to humidity1_input sysfs attribute. 153 * Returns number of bytes written into buffer, negative errno on error. 154 */ 155 static ssize_t sht21_show_humidity(struct device *dev, 156 struct device_attribute *attr, 157 char *buf) 158 { 159 struct sht21 *sht21 = dev_get_drvdata(dev); 160 int ret; 161 162 ret = sht21_update_measurements(dev); 163 if (ret < 0) 164 return ret; 165 return sprintf(buf, "%d\n", sht21->humidity); 166 } 167 168 /* sysfs attributes */ 169 static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO, sht21_show_temperature, 170 NULL, 0); 171 static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO, sht21_show_humidity, 172 NULL, 0); 173 174 static struct attribute *sht21_attrs[] = { 175 &sensor_dev_attr_temp1_input.dev_attr.attr, 176 &sensor_dev_attr_humidity1_input.dev_attr.attr, 177 NULL 178 }; 179 180 ATTRIBUTE_GROUPS(sht21); 181 182 static int sht21_probe(struct i2c_client *client, 183 const struct i2c_device_id *id) 184 { 185 struct device *dev = &client->dev; 186 struct device *hwmon_dev; 187 struct sht21 *sht21; 188 189 if (!i2c_check_functionality(client->adapter, 190 I2C_FUNC_SMBUS_WORD_DATA)) { 191 dev_err(&client->dev, 192 "adapter does not support SMBus word transactions\n"); 193 return -ENODEV; 194 } 195 196 sht21 = devm_kzalloc(dev, sizeof(*sht21), GFP_KERNEL); 197 if (!sht21) 198 return -ENOMEM; 199 200 sht21->client = client; 201 202 mutex_init(&sht21->lock); 203 204 hwmon_dev = devm_hwmon_device_register_with_groups(dev, client->name, 205 sht21, sht21_groups); 206 return PTR_ERR_OR_ZERO(hwmon_dev); 207 } 208 209 /* Device ID table */ 210 static const struct i2c_device_id sht21_id[] = { 211 { "sht21", 0 }, 212 { } 213 }; 214 MODULE_DEVICE_TABLE(i2c, sht21_id); 215 216 static struct i2c_driver sht21_driver = { 217 .driver.name = "sht21", 218 .probe = sht21_probe, 219 .id_table = sht21_id, 220 }; 221 222 module_i2c_driver(sht21_driver); 223 224 MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>"); 225 MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver"); 226 MODULE_LICENSE("GPL"); 227