--- /dev/null
+/* Sensirion SHT21 humidity and temperature sensor driver
+ *
+ * Copyright (C) 2010 Urs Fleisch <urs.fleisch@sensirion.com>
+ *
+ * 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 - SHT21 device specific data
+ * @hwmon_dev: device registered with hwmon
+ * @lock: mutex to protect measurement values
+ * @valid: only 0 before first measurement is taken
+ * @last_update: time of last update (jiffies)
+ * @temperature: cached temperature measurement value
+ * @humidity: cached humidity measurement value
+ */
+struct sht21 {
+ struct i2c_client *client;
+ struct mutex lock;
+ char valid;
+ unsigned long last_update;
+ int temperature;
+ int humidity;
+};
+
+/**
+ * sht21_temp_ticks_to_millicelsius() - convert raw temperature ticks to
+ * milli celsius
+ * @ticks: temperature ticks value received from sensor
+ */
+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;
+}
+
+/**
+ * sht21_rh_ticks_to_per_cent_mille() - convert raw humidity ticks to
+ * one-thousandths of a percent relative humidity
+ * @ticks: humidity ticks value received from sensor
+ */
+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;
+}
+
+/**
+ * sht21_update_measurements() - get updated measurements from device
+ * @dev: device
+ *
+ * Returns 0 on success, else negative errno.
+ */
+static int sht21_update_measurements(struct device *dev)
+{
+ int ret = 0;
+ struct sht21 *sht21 = dev_get_drvdata(dev);
+ struct i2c_client *client = sht21->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;
+}
+
+/**
+ * sht21_show_temperature() - show temperature measurement value in sysfs
+ * @dev: device
+ * @attr: device attribute
+ * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
+ *
+ * Will be called on read access to temp1_input sysfs attribute.
+ * Returns number of bytes written into buffer, negative errno on error.
+ */
+static ssize_t sht21_show_temperature(struct device *dev,
+ struct device_attribute *attr,
+ char *buf)
+{
+ struct sht21 *sht21 = dev_get_drvdata(dev);
+ int ret;
+
+ ret = sht21_update_measurements(dev);
+ if (ret < 0)
+ return ret;
+ return sprintf(buf, "%d\n", sht21->temperature);
+}
+
+/**
+ * sht21_show_humidity() - show humidity measurement value in sysfs
+ * @dev: device
+ * @attr: device attribute
+ * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
+ *
+ * Will be called on read access to humidity1_input sysfs attribute.
+ * Returns number of bytes written into buffer, negative errno on error.
+ */
+static ssize_t sht21_show_humidity(struct device *dev,
+ struct device_attribute *attr,
+ char *buf)
+{
+ struct sht21 *sht21 = dev_get_drvdata(dev);
+ int ret;
+
+ ret = sht21_update_measurements(dev);
+ 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_attrs[] = {
+ &sensor_dev_attr_temp1_input.dev_attr.attr,
+ &sensor_dev_attr_humidity1_input.dev_attr.attr,
+ NULL
+};
+
+ATTRIBUTE_GROUPS(sht21);
+
+static int sht21_probe(struct i2c_client *client,
+ const struct i2c_device_id *id)
+{
+ struct device *dev = &client->dev;
+ struct device *hwmon_dev;
+ struct sht21 *sht21;
+
+ 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(dev, sizeof(*sht21), GFP_KERNEL);
+ if (!sht21)
+ return -ENOMEM;
+
+ sht21->client = client;
+
+ mutex_init(&sht21->lock);
+
+ hwmon_dev = devm_hwmon_device_register_with_groups(dev, client->name,
+ sht21, sht21_groups);
+ return PTR_ERR_OR_ZERO(hwmon_dev);
+}
+
+/* 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,
+ .id_table = sht21_id,
+};
+
+module_i2c_driver(sht21_driver);
+
+MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>");
+MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver");
+MODULE_LICENSE("GPL");
Code Review / kvmfornfv.git / blobdiff