sht21.c

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/* Sensirion SHT21 humidity and temperature sensor driver
 *
 * Copyright (C) 2010 Urs Fleisch <[email protected]>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA
 *
 * Data sheet available (5/2010) at
 * http://www.sensirion.com/en/pdf/product_information/Datasheet-humidity-sensor-SHT21.pdf
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/i2c.h>
#include <linux/hwmon.h>
#include <linux/hwmon-sysfs.h>
#include <linux/err.h>
#include <linux/mutex.h>
#include <linux/device.h>
#include <linux/jiffies.h>

/* I2C command bytes */
#define SHT21_TRIG_T_MEASUREMENT_HM  0xe3
#define SHT21_TRIG_RH_MEASUREMENT_HM 0xe5

struct sht21 {
    struct device *hwmon_dev;
    struct mutex lock;
    char valid;
    unsigned long last_update;
    int temperature;
    int humidity;
};

static inline int sht21_temp_ticks_to_millicelsius(int ticks)
{
    ticks &= ~0x0003; /* clear status bits */
    /*
     * Formula T = -46.85 + 175.72 * ST / 2^16 from data sheet 6.2,
     * optimized for integer fixed point (3 digits) arithmetic
     */
    return ((21965 * ticks) >> 13) - 46850;
}

static inline int sht21_rh_ticks_to_per_cent_mille(int ticks)
{
    ticks &= ~0x0003; /* clear status bits */
    /*
     * Formula RH = -6 + 125 * SRH / 2^16 from data sheet 6.1,
     * optimized for integer fixed point (3 digits) arithmetic
     */
    return ((15625 * ticks) >> 13) - 6000;
}

static int sht21_update_measurements(struct i2c_client *client)
{
    int ret = 0;
    struct sht21 *sht21 = i2c_get_clientdata(client);

    mutex_lock(&sht21->lock);
    /*
     * Data sheet 2.4:
     * SHT2x should not be active for more than 10% of the time - e.g.
     * maximum two measurements per second at 12bit accuracy shall be made.
     */
    if (time_after(jiffies, sht21->last_update + HZ / 2) || !sht21->valid) {
        ret = i2c_smbus_read_word_swapped(client,
                          SHT21_TRIG_T_MEASUREMENT_HM);
        if (ret < 0)
            goto out;
        sht21->temperature = sht21_temp_ticks_to_millicelsius(ret);
        ret = i2c_smbus_read_word_swapped(client,
                          SHT21_TRIG_RH_MEASUREMENT_HM);
        if (ret < 0)
            goto out;
        sht21->humidity = sht21_rh_ticks_to_per_cent_mille(ret);
        sht21->last_update = jiffies;
        sht21->valid = 1;
    }
out:
    mutex_unlock(&sht21->lock);

    return ret >= 0 ? 0 : ret;
}

static ssize_t sht21_show_temperature(struct device *dev,
    struct device_attribute *attr,
    char *buf)
{
    struct i2c_client *client = to_i2c_client(dev);
    struct sht21 *sht21 = i2c_get_clientdata(client);
    int ret = sht21_update_measurements(client);
    if (ret < 0)
        return ret;
    return sprintf(buf, "%d\n", sht21->temperature);
}

static ssize_t sht21_show_humidity(struct device *dev,
    struct device_attribute *attr,
    char *buf)
{
    struct i2c_client *client = to_i2c_client(dev);
    struct sht21 *sht21 = i2c_get_clientdata(client);
    int ret = sht21_update_measurements(client);
    if (ret < 0)
        return ret;
    return sprintf(buf, "%d\n", sht21->humidity);
}

/* sysfs attributes */
static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO, sht21_show_temperature,
    NULL, 0);
static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO, sht21_show_humidity,
    NULL, 0);

static struct attribute *sht21_attributes[] = {
    &sensor_dev_attr_temp1_input.dev_attr.attr,
    &sensor_dev_attr_humidity1_input.dev_attr.attr,
    NULL
};

static const struct attribute_group sht21_attr_group = {
    .attrs = sht21_attributes,
};

static int __devinit sht21_probe(struct i2c_client *client,
    const struct i2c_device_id *id)
{
    struct sht21 *sht21;
    int err;

    if (!i2c_check_functionality(client->adapter,
                     I2C_FUNC_SMBUS_WORD_DATA)) {
        dev_err(&client->dev,
            "adapter does not support SMBus word transactions\n");
        return -ENODEV;
    }

    sht21 = devm_kzalloc(&client->dev, sizeof(*sht21), GFP_KERNEL);
    if (!sht21)
        return -ENOMEM;

    i2c_set_clientdata(client, sht21);

    mutex_init(&sht21->lock);

    err = sysfs_create_group(&client->dev.kobj, &sht21_attr_group);
    if (err) {
        dev_dbg(&client->dev, "could not create sysfs files\n");
        return err;
    }
    sht21->hwmon_dev = hwmon_device_register(&client->dev);
    if (IS_ERR(sht21->hwmon_dev)) {
        dev_dbg(&client->dev, "unable to register hwmon device\n");
        err = PTR_ERR(sht21->hwmon_dev);
        goto fail_remove_sysfs;
    }

    dev_info(&client->dev, "initialized\n");

    return 0;

fail_remove_sysfs:
    sysfs_remove_group(&client->dev.kobj, &sht21_attr_group);
    return err;
}

static int __devexit sht21_remove(struct i2c_client *client)
{
    struct sht21 *sht21 = i2c_get_clientdata(client);

    hwmon_device_unregister(sht21->hwmon_dev);
    sysfs_remove_group(&client->dev.kobj, &sht21_attr_group);

    return 0;
}

/* Device ID table */
static const struct i2c_device_id sht21_id[] = {
    { "sht21", 0 },
    { }
};
MODULE_DEVICE_TABLE(i2c, sht21_id);

static struct i2c_driver sht21_driver = {
    .driver.name = "sht21",
    .probe       = sht21_probe,
    .remove      = __devexit_p(sht21_remove),
    .id_table    = sht21_id,
};

module_i2c_driver(sht21_driver);

MODULE_AUTHOR("Urs Fleisch <[email protected]>");
MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver");
MODULE_LICENSE("GPL");