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1// SPDX-License-Identifier: GPL-2.0-or-later2/* Sensirion SHT21 humidity and temperature sensor driver3 *4 * Copyright (C) 2010 Urs Fleisch <urs.fleisch@sensirion.com>5 *6 * Data sheet available at https://www.sensirion.com/file/datasheet_sht217 */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 0xe322#define SHT21_TRIG_RH_MEASUREMENT_HM 0xe523#define SHT21_READ_SNB_CMD1 0xFA24#define SHT21_READ_SNB_CMD2 0x0F25#define SHT21_READ_SNAC_CMD1 0xFC26#define SHT21_READ_SNAC_CMD2 0xC927 28/**29 * struct sht21 - SHT21 device specific data30 * @client: I2C client device31 * @lock: mutex to protect measurement values32 * @last_update: time of last update (jiffies)33 * @temperature: cached temperature measurement value34 * @humidity: cached humidity measurement value35 * @valid: only 0 before first measurement is taken36 * @eic: cached electronic identification code text37 */38struct sht21 {39 struct i2c_client *client;40 struct mutex lock;41 unsigned long last_update;42 int temperature;43 int humidity;44 bool valid;45 char eic[18];46};47 48/**49 * sht21_temp_ticks_to_millicelsius() - convert raw temperature ticks to50 * milli celsius51 * @ticks: temperature ticks value received from sensor52 */53static 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) arithmetic59 */60 return ((21965 * ticks) >> 13) - 46850;61}62 63/**64 * sht21_rh_ticks_to_per_cent_mille() - convert raw humidity ticks to65 * one-thousandths of a percent relative humidity66 * @ticks: humidity ticks value received from sensor67 */68static 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) arithmetic74 */75 return ((15625 * ticks) >> 13) - 6000;76}77 78/**79 * sht21_update_measurements() - get updated measurements from device80 * @dev: device81 *82 * Returns 0 on success, else negative errno.83 */84static 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 = true;109 }110out:111 mutex_unlock(&sht21->lock);112 113 return ret >= 0 ? 0 : ret;114}115 116/**117 * sht21_temperature_show() - show temperature measurement value in sysfs118 * @dev: device119 * @attr: device attribute120 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to121 *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 */125static 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_humidity_show() - show humidity measurement value in sysfs140 * @dev: device141 * @attr: device attribute142 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to143 *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 */147static 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 159static 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), "%8phN\n", eic);203out:204 if (ret < 0)205 sht21->eic[0] = 0;206 207 return ret;208}209 210/**211 * eic_show() - show Electronic Identification Code in sysfs212 * @dev: device213 * @attr: device attribute214 * @buf: sysfs buffer (PAGE_SIZE) where EIC is written215 *216 * Will be called on read access to eic sysfs attribute.217 * Returns number of bytes written into buffer, negative errno on error.218 */219static ssize_t eic_show(struct device *dev,220 struct device_attribute *attr,221 char *buf)222{223 struct sht21 *sht21 = dev_get_drvdata(dev);224 int ret;225 226 ret = sizeof(sht21->eic) - 1;227 mutex_lock(&sht21->lock);228 if (!sht21->eic[0])229 ret = eic_read(sht21);230 if (ret > 0)231 memcpy(buf, sht21->eic, ret);232 mutex_unlock(&sht21->lock);233 return ret;234}235 236/* sysfs attributes */237static SENSOR_DEVICE_ATTR_RO(temp1_input, sht21_temperature, 0);238static SENSOR_DEVICE_ATTR_RO(humidity1_input, sht21_humidity, 0);239static DEVICE_ATTR_RO(eic);240 241static struct attribute *sht21_attrs[] = {242 &sensor_dev_attr_temp1_input.dev_attr.attr,243 &sensor_dev_attr_humidity1_input.dev_attr.attr,244 &dev_attr_eic.attr,245 NULL246};247 248ATTRIBUTE_GROUPS(sht21);249 250static int sht21_probe(struct i2c_client *client)251{252 struct device *dev = &client->dev;253 struct device *hwmon_dev;254 struct sht21 *sht21;255 256 if (!i2c_check_functionality(client->adapter,257 I2C_FUNC_SMBUS_WORD_DATA)) {258 dev_err(&client->dev,259 "adapter does not support SMBus word transactions\n");260 return -ENODEV;261 }262 263 sht21 = devm_kzalloc(dev, sizeof(*sht21), GFP_KERNEL);264 if (!sht21)265 return -ENOMEM;266 267 sht21->client = client;268 269 mutex_init(&sht21->lock);270 271 hwmon_dev = devm_hwmon_device_register_with_groups(dev, client->name,272 sht21, sht21_groups);273 return PTR_ERR_OR_ZERO(hwmon_dev);274}275 276/* Device ID table */277static const struct i2c_device_id sht21_id[] = {278 { "sht21" },279 { }280};281MODULE_DEVICE_TABLE(i2c, sht21_id);282 283static struct i2c_driver sht21_driver = {284 .driver.name = "sht21",285 .probe = sht21_probe,286 .id_table = sht21_id,287};288 289module_i2c_driver(sht21_driver);290 291MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>");292MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver");293MODULE_LICENSE("GPL");294