hih6130.c

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/* Honeywell HIH-6130/HIH-6131 humidity and temperature sensor driver
 *
 * Copyright (C) 2012 Iain Paton <[email protected]>
 *
 * heavily based on the sht21 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 sheets available (2012-06-22) at
 * http://sensing.honeywell.com/index.php?ci_id=3106&la_id=1&defId=44872
 */

#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/delay.h>
#include <linux/jiffies.h>

struct hih6130 {
    struct device *hwmon_dev;
    struct mutex lock;
    bool valid;
    unsigned long last_update;
    int temperature;
    int humidity;
};

static inline int hih6130_temp_ticks_to_millicelsius(int ticks)
{

    ticks = ticks >> 2;
    /*
     * from data sheet section 5.0
     * Formula T = ( ticks / ( 2^14 - 2 ) ) * 165 -40
     */
    return (DIV_ROUND_CLOSEST(ticks * 1650, 16382) - 400) * 100;
}

static inline int hih6130_rh_ticks_to_per_cent_mille(int ticks)
{

    ticks &= ~0xC000; /* clear status bits */
    /*
     * from data sheet section 4.0
     * Formula RH = ( ticks / ( 2^14 -2 ) ) * 100
     */
    return DIV_ROUND_CLOSEST(ticks * 1000, 16382) * 100;
}

static int hih6130_update_measurements(struct i2c_client *client)
{
    int ret = 0;
    int t;
    struct hih6130 *hih6130 = i2c_get_clientdata(client);
    unsigned char tmp[4];
    struct i2c_msg msgs[1] = {
        {
            .addr = client->addr,
            .flags = I2C_M_RD,
            .len = 4,
            .buf = tmp,
        }
    };

    mutex_lock(&hih6130->lock);

    /*
     * While the measurement can be completed in ~40ms the sensor takes
     * much longer to react to a change in external conditions. How quickly
     * it reacts depends on airflow and other factors outwith our control.
     * The datasheet specifies maximum 'Response time' for humidity at 8s
     * and temperature at 30s under specified conditions.
     * We therefore choose to only read the sensor at most once per second.
     * This trades off pointless activity polling the sensor much faster
     * than it can react against better response times in conditions more
     * favourable than specified in the datasheet.
     */
    if (time_after(jiffies, hih6130->last_update + HZ) || !hih6130->valid) {

        /* write to slave address, no data, to request a measurement */
        ret = i2c_master_send(client, tmp, 0);
        if (ret < 0)
            goto out;

        /* measurement cycle time is ~36.65msec */
        msleep(40);

        ret = i2c_transfer(client->adapter, msgs, 1);
        if (ret < 0)
            goto out;

        if ((tmp[0] & 0xC0) != 0) {
            dev_err(&client->dev, "Error while reading measurement result\n");
            ret = -EIO;
            goto out;
        }

        t = (tmp[0] << 8) + tmp[1];
        hih6130->humidity = hih6130_rh_ticks_to_per_cent_mille(t);

        t = (tmp[2] << 8) + tmp[3];
        hih6130->temperature = hih6130_temp_ticks_to_millicelsius(t);

        hih6130->last_update = jiffies;
        hih6130->valid = true;
    }
out:
    mutex_unlock(&hih6130->lock);

    return ret >= 0 ? 0 : ret;
}

static ssize_t hih6130_show_temperature(struct device *dev,
                    struct device_attribute *attr,
                    char *buf)
{
    struct i2c_client *client = to_i2c_client(dev);
    struct hih6130 *hih6130 = i2c_get_clientdata(client);
    int ret = hih6130_update_measurements(client);
    if (ret < 0)
        return ret;
    return sprintf(buf, "%d\n", hih6130->temperature);
}

static ssize_t hih6130_show_humidity(struct device *dev,
                     struct device_attribute *attr, char *buf)
{
    struct i2c_client *client = to_i2c_client(dev);
    struct hih6130 *hih6130 = i2c_get_clientdata(client);
    int ret = hih6130_update_measurements(client);
    if (ret < 0)
        return ret;
    return sprintf(buf, "%d\n", hih6130->humidity);
}

/* sysfs attributes */
static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO, hih6130_show_temperature,
    NULL, 0);
static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO, hih6130_show_humidity,
    NULL, 0);

static struct attribute *hih6130_attributes[] = {
    &sensor_dev_attr_temp1_input.dev_attr.attr,
    &sensor_dev_attr_humidity1_input.dev_attr.attr,
    NULL
};

static const struct attribute_group hih6130_attr_group = {
    .attrs = hih6130_attributes,
};

static int __devinit hih6130_probe(struct i2c_client *client,
                   const struct i2c_device_id *id)
{
    struct hih6130 *hih6130;
    int err;

    if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C)) {
        dev_err(&client->dev, "adapter does not support true I2C\n");
        return -ENODEV;
    }

    hih6130 = devm_kzalloc(&client->dev, sizeof(*hih6130), GFP_KERNEL);
    if (!hih6130)
        return -ENOMEM;

    i2c_set_clientdata(client, hih6130);

    mutex_init(&hih6130->lock);

    err = sysfs_create_group(&client->dev.kobj, &hih6130_attr_group);
    if (err) {
        dev_dbg(&client->dev, "could not create sysfs files\n");
        return err;
    }

    hih6130->hwmon_dev = hwmon_device_register(&client->dev);
    if (IS_ERR(hih6130->hwmon_dev)) {
        dev_dbg(&client->dev, "unable to register hwmon device\n");
        err = PTR_ERR(hih6130->hwmon_dev);
        goto fail_remove_sysfs;
    }

    return 0;

fail_remove_sysfs:
    sysfs_remove_group(&client->dev.kobj, &hih6130_attr_group);
    return err;
}

static int __devexit hih6130_remove(struct i2c_client *client)
{
    struct hih6130 *hih6130 = i2c_get_clientdata(client);

    hwmon_device_unregister(hih6130->hwmon_dev);
    sysfs_remove_group(&client->dev.kobj, &hih6130_attr_group);

    return 0;
}

/* Device ID table */
static const struct i2c_device_id hih6130_id[] = {
    { "hih6130", 0 },
    { }
};
MODULE_DEVICE_TABLE(i2c, hih6130_id);

static struct i2c_driver hih6130_driver = {
    .driver.name = "hih6130",
    .probe       = hih6130_probe,
    .remove      = __devexit_p(hih6130_remove),
    .id_table    = hih6130_id,
};

module_i2c_driver(hih6130_driver);

MODULE_AUTHOR("Iain Paton <[email protected]>");
MODULE_DESCRIPTION("Honeywell HIH-6130 humidity and temperature sensor driver");
MODULE_LICENSE("GPL");