--- /dev/null
+Kernel driver htu21
+===================
+
+Supported chips:
+ * Measurement Specialties HTU21D
+ Prefix: 'htu21'
+ Addresses scanned: none
+ Datasheet: Publicly available at the Measurement Specialties website
+ http://www.meas-spec.com/downloads/HTU21D.pdf
+
+
+Author:
+ William Markezana <william.markezana@meas-spec.com>
+
+Description
+-----------
+
+The HTU21D is a humidity and temperature sensor in a DFN package of
+only 3 x 3 mm footprint and 0.9 mm height.
+
+The devices communicate with the I2C protocol. All sensors are set to the
+same I2C address 0x40, so an entry with I2C_BOARD_INFO("htu21", 0x40) can
+be used in the board setup code.
+
+This driver does not auto-detect devices. You will have to instantiate the
+devices explicitly. Please see Documentation/i2c/instantiating-devices
+for details.
+
+sysfs-Interface
+---------------
+
+temp1_input - temperature input
+humidity1_input - humidity input
+
+Notes
+-----
+
+The driver uses the default resolution settings of 12 bit for humidity and 14
+bit for temperature, which results in typical measurement times of 11 ms for
+humidity and 44 ms for temperature. To keep self heating below 0.1 degree
+Celsius, the device should not be active for more than 10% of the time. For
+this reason, the driver performs no more than two measurements per second and
+reports cached information if polled more frequently.
+
+Different resolutions, the on-chip heater, using the CRC checksum and reading
+the serial number are not supported yet.
--- /dev/null
+/*
+ * Measurement Specialties HTU21D humidity and temperature sensor driver
+ *
+ * Copyright (C) 2013 William Markezana <william.markezana@meas-spec.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.
+ *
+ */
+
+#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>
+
+/* HTU21 Commands */
+#define HTU21_T_MEASUREMENT_HM 0xE3
+#define HTU21_RH_MEASUREMENT_HM 0xE5
+
+struct htu21 {
+ struct device *hwmon_dev;
+ struct mutex lock;
+ bool valid;
+ unsigned long last_update;
+ int temperature;
+ int humidity;
+};
+
+static inline int htu21_temp_ticks_to_millicelsius(int ticks)
+{
+ ticks &= ~0x0003; /* clear status bits */
+ /*
+ * Formula T = -46.85 + 175.72 * ST / 2^16 from datasheet p14,
+ * optimized for integer fixed point (3 digits) arithmetic
+ */
+ return ((21965 * ticks) >> 13) - 46850;
+}
+
+static inline int htu21_rh_ticks_to_per_cent_mille(int ticks)
+{
+ ticks &= ~0x0003; /* clear status bits */
+ /*
+ * Formula RH = -6 + 125 * SRH / 2^16 from datasheet p14,
+ * optimized for integer fixed point (3 digits) arithmetic
+ */
+ return ((15625 * ticks) >> 13) - 6000;
+}
+
+static int htu21_update_measurements(struct i2c_client *client)
+{
+ int ret = 0;
+ struct htu21 *htu21 = i2c_get_clientdata(client);
+
+ mutex_lock(&htu21->lock);
+
+ if (time_after(jiffies, htu21->last_update + HZ / 2) ||
+ !htu21->valid) {
+ ret = i2c_smbus_read_word_swapped(client,
+ HTU21_T_MEASUREMENT_HM);
+ if (ret < 0)
+ goto out;
+ htu21->temperature = htu21_temp_ticks_to_millicelsius(ret);
+ ret = i2c_smbus_read_word_swapped(client,
+ HTU21_RH_MEASUREMENT_HM);
+ if (ret < 0)
+ goto out;
+ htu21->humidity = htu21_rh_ticks_to_per_cent_mille(ret);
+ htu21->last_update = jiffies;
+ htu21->valid = true;
+ }
+out:
+ mutex_unlock(&htu21->lock);
+
+ return ret >= 0 ? 0 : ret;
+}
+
+static ssize_t htu21_show_temperature(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ struct i2c_client *client = to_i2c_client(dev);
+ struct htu21 *htu21 = i2c_get_clientdata(client);
+ int ret = htu21_update_measurements(client);
+ if (ret < 0)
+ return ret;
+ return sprintf(buf, "%d\n", htu21->temperature);
+}
+
+static ssize_t htu21_show_humidity(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ struct i2c_client *client = to_i2c_client(dev);
+ struct htu21 *htu21 = i2c_get_clientdata(client);
+ int ret = htu21_update_measurements(client);
+ if (ret < 0)
+ return ret;
+ return sprintf(buf, "%d\n", htu21->humidity);
+}
+
+static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO,
+ htu21_show_temperature, NULL, 0);
+static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO,
+ htu21_show_humidity, NULL, 0);
+
+static struct attribute *htu21_attributes[] = {
+ &sensor_dev_attr_temp1_input.dev_attr.attr,
+ &sensor_dev_attr_humidity1_input.dev_attr.attr,
+ NULL
+};
+
+static const struct attribute_group htu21_group = {
+ .attrs = htu21_attributes,
+};
+
+static int htu21_probe(struct i2c_client *client,
+ const struct i2c_device_id *id)
+{
+ struct htu21 *htu21;
+ int err;
+
+ if (!i2c_check_functionality(client->adapter,
+ I2C_FUNC_SMBUS_READ_WORD_DATA)) {
+ dev_err(&client->dev,
+ "adapter does not support SMBus word transactions\n");
+ return -ENODEV;
+ }
+
+ htu21 = devm_kzalloc(&client->dev, sizeof(*htu21), GFP_KERNEL);
+ if (!htu21)
+ return -ENOMEM;
+
+ i2c_set_clientdata(client, htu21);
+
+ mutex_init(&htu21->lock);
+
+ err = sysfs_create_group(&client->dev.kobj, &htu21_group);
+ if (err) {
+ dev_dbg(&client->dev, "could not create sysfs files\n");
+ return err;
+ }
+ htu21->hwmon_dev = hwmon_device_register(&client->dev);
+ if (IS_ERR(htu21->hwmon_dev)) {
+ dev_dbg(&client->dev, "unable to register hwmon device\n");
+ err = PTR_ERR(htu21->hwmon_dev);
+ goto error;
+ }
+
+ dev_info(&client->dev, "initialized\n");
+
+ return 0;
+
+error:
+ sysfs_remove_group(&client->dev.kobj, &htu21_group);
+ return err;
+}
+
+static int htu21_remove(struct i2c_client *client)
+{
+ struct htu21 *htu21 = i2c_get_clientdata(client);
+
+ hwmon_device_unregister(htu21->hwmon_dev);
+ sysfs_remove_group(&client->dev.kobj, &htu21_group);
+
+ return 0;
+}
+
+static const struct i2c_device_id htu21_id[] = {
+ { "htu21", 0 },
+ { }
+};
+MODULE_DEVICE_TABLE(i2c, htu21_id);
+
+static struct i2c_driver htu21_driver = {
+ .class = I2C_CLASS_HWMON,
+ .driver = {
+ .name = "htu21",
+ },
+ .probe = htu21_probe,
+ .remove = htu21_remove,
+ .id_table = htu21_id,
+};
+
+module_i2c_driver(htu21_driver);
+
+MODULE_AUTHOR("William Markezana <william.markezana@meas-spec.com>");
+MODULE_DESCRIPTION("MEAS HTU21D humidity and temperature sensor driver");
+MODULE_LICENSE("GPL");
projects / kernel.git / commitdiff