hwmon: add support for Sensirion SHT3x sensors

This driver implements support for the Sensirion SHT3x-DIS chip,
a humidity and temperature sensor. Temperature is measured
in degrees celsius, relative humidity is expressed as a percentage.
In the sysfs interface, all values are scaled by 1000,
i.e. the value for 31.5 degrees celsius is 31500.

Signed-off-by: Pascal Sachs <pascal.sachs@sensirion.com>
[groeck: Fixed 'Variable length array is used' gcc warning]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

5 files changed, 834 insertions, 0 deletions

diff --git a/Documentation/hwmon/sht3x b/Documentation/hwmon/sht3x
new file mode 100644
index 000000000000..f5aa633ed383
--- /dev/null
+++ b/Documentation/hwmon/sht3x
@@ -0,0 +1,72 @@
+Kernel driver sht3x
+===================
+
+Supported chips:
+  * Sensirion SHT3x-DIS
+    Prefix: 'sht3x'
+    Addresses scanned: none
+    Datasheet: http://www.sensirion.com/fileadmin/user_upload/customers/sensirion/Dokumente/Humidity/Sensirion_Humidity_Datasheet_SHT3x_DIS.pdf
+
+Author:
+  David Frey <david.frey@sensirion.com>
+  Pascal Sachs <pascal.sachs@sensirion.com>
+
+Description
+-----------
+
+This driver implements support for the Sensirion SHT3x-DIS chip, a humidity
+and temperature sensor. Temperature is measured in degrees celsius, relative
+humidity is expressed as a percentage. In the sysfs interface, all values are
+scaled by 1000, i.e. the value for 31.5 degrees celsius is 31500.
+
+The device communicates with the I2C protocol. Sensors can have the I2C
+addresses 0x44 or 0x45, depending on the wiring. See
+Documentation/i2c/instantiating-devices for methods to instantiate the device.
+
+There are two options configurable by means of sht3x_platform_data:
+1. blocking (pull the I2C clock line down while performing the measurement) or
+   non-blocking mode. Blocking mode will guarantee the fastest result but
+   the I2C bus will be busy during that time. By default, non-blocking mode
+   is used. Make sure clock-stretching works properly on your device if you
+   want to use blocking mode.
+2. high or low accuracy. High accuracy is used by default and using it is
+   strongly recommended.
+
+The sht3x sensor supports a single shot mode as well as 5 periodic measure
+modes, which can be controlled with the update_interval sysfs interface.
+The allowed update_interval in milliseconds are as follows:
+  *     0   single shot mode
+  *  2000   0.5 Hz periodic measurement
+  *  1000   1   Hz periodic measurement
+  *   500   2   Hz periodic measurement
+  *   250   4   Hz periodic measurement
+  *   100  10   Hz periodic measurement
+
+In the periodic measure mode, the sensor automatically triggers a measurement
+with the configured update interval on the chip. When a temperature or humidity
+reading exceeds the configured limits, the alert attribute is set to 1 and
+the alert pin on the sensor is set to high.
+When the temperature and humidity readings move back between the hysteresis
+values, the alert bit is set to 0 and the alert pin on the sensor is set to
+low.
+
+sysfs-Interface
+---------------
+
+temp1_input:        temperature input
+humidity1_input:    humidity input
+temp1_max:          temperature max value
+temp1_max_hyst:     temperature hysteresis value for max limit
+humidity1_max:      humidity max value
+humidity1_max_hyst: humidity hysteresis value for max limit
+temp1_min:          temperature min value
+temp1_min_hyst:     temperature hysteresis value for min limit
+humidity1_min:      humidity min value
+humidity1_min_hyst: humidity hysteresis value for min limit
+temp1_alarm:        alarm flag is set to 1 if the temperature is outside the
+                    configured limits. Alarm only works in periodic measure mode
+humidity1_alarm:    alarm flag is set to 1 if the humidity is outside the
+                    configured limits. Alarm only works in periodic measure mode
+update_interval:    update interval, 0 for single shot, interval in msec
+                    for periodic measurement. If the interval is not supported
+                    by the sensor, the next faster interval is chosen
diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
index ff940075bb90..e0be99a4615c 100644
--- a/drivers/hwmon/Kconfig
+++ b/drivers/hwmon/Kconfig
@@ -1265,6 +1265,17 @@ config SENSORS_SHT21
 	  This driver can also be built as a module.  If so, the module
 	  will be called sht21.
 
+config SENSORS_SHT3x
+	tristate "Sensiron humidity and temperature sensors. SHT3x and compat."
+	depends on I2C
+	select CRC8
+	help
+	  If you say yes here you get support for the Sensiron SHT30 and SHT31
+	  humidity and temperature sensors.
+
+	  This driver can also be built as a module.  If so, the module
+	  will be called sht3x.
+
 config SENSORS_SHTC1
 	tristate "Sensiron humidity and temperature sensors. SHTC1 and compat."
 	depends on I2C
diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
index 2ef5b7c4c54f..406b18b995b3 100644
--- a/drivers/hwmon/Makefile
+++ b/drivers/hwmon/Makefile
@@ -138,6 +138,7 @@ obj-$(CONFIG_SENSORS_SCH5627)	+= sch5627.o
 obj-$(CONFIG_SENSORS_SCH5636)	+= sch5636.o
 obj-$(CONFIG_SENSORS_SHT15)	+= sht15.o
 obj-$(CONFIG_SENSORS_SHT21)	+= sht21.o
+obj-$(CONFIG_SENSORS_SHT3x)	+= sht3x.o
 obj-$(CONFIG_SENSORS_SHTC1)	+= shtc1.o
 obj-$(CONFIG_SENSORS_SIS5595)	+= sis5595.o
 obj-$(CONFIG_SENSORS_SMM665)	+= smm665.o
diff --git a/drivers/hwmon/sht3x.c b/drivers/hwmon/sht3x.c
new file mode 100644
index 000000000000..707a3f85385b
--- /dev/null
+++ b/drivers/hwmon/sht3x.c
@@ -0,0 +1,725 @@
+/* Sensirion SHT3x-DIS humidity and temperature sensor driver.
+ * The SHT3x comes in many different versions, this driver is for the
+ * I2C version only.
+ *
+ * Copyright (C) 2016 Sensirion AG, Switzerland
+ * Author: David Frey <david.frey@sensirion.com>
+ * Author: Pascal Sachs <pascal.sachs@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.
+ *
+ */
+
+#include <asm/page.h>
+#include <linux/crc8.h>
+#include <linux/delay.h>
+#include <linux/err.h>
+#include <linux/hwmon.h>
+#include <linux/hwmon-sysfs.h>
+#include <linux/i2c.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/jiffies.h>
+#include <linux/platform_data/sht3x.h>
+
+/* commands (high precision mode) */
+static const unsigned char sht3x_cmd_measure_blocking_hpm[]    = { 0x2c, 0x06 };
+static const unsigned char sht3x_cmd_measure_nonblocking_hpm[] = { 0x24, 0x00 };
+
+/* commands (low power mode) */
+static const unsigned char sht3x_cmd_measure_blocking_lpm[]    = { 0x2c, 0x10 };
+static const unsigned char sht3x_cmd_measure_nonblocking_lpm[] = { 0x24, 0x16 };
+
+/* commands for periodic mode */
+static const unsigned char sht3x_cmd_measure_periodic_mode[]   = { 0xe0, 0x00 };
+static const unsigned char sht3x_cmd_break[]                   = { 0x30, 0x93 };
+
+/* other commands */
+static const unsigned char sht3x_cmd_read_status_reg[]         = { 0xf3, 0x2d };
+static const unsigned char sht3x_cmd_clear_status_reg[]        = { 0x30, 0x41 };
+
+/* delays for non-blocking i2c commands, both in us */
+#define SHT3X_NONBLOCKING_WAIT_TIME_HPM  15000
+#define SHT3X_NONBLOCKING_WAIT_TIME_LPM   4000
+
+#define SHT3X_WORD_LEN         2
+#define SHT3X_CMD_LENGTH       2
+#define SHT3X_CRC8_LEN         1
+#define SHT3X_RESPONSE_LENGTH  6
+#define SHT3X_CRC8_POLYNOMIAL  0x31
+#define SHT3X_CRC8_INIT        0xFF
+#define SHT3X_MIN_TEMPERATURE  -45000
+#define SHT3X_MAX_TEMPERATURE  130000
+#define SHT3X_MIN_HUMIDITY     0
+#define SHT3X_MAX_HUMIDITY     100000
+
+enum sht3x_chips {
+	sht3x,
+	sts3x,
+};
+
+enum sht3x_limits {
+	limit_max = 0,
+	limit_max_hyst,
+	limit_min,
+	limit_min_hyst,
+};
+
+DECLARE_CRC8_TABLE(sht3x_crc8_table);
+
+/* periodic measure commands (high precision mode) */
+static const char periodic_measure_commands_hpm[][SHT3X_CMD_LENGTH] = {
+	/* 0.5 measurements per second */
+	{0x20, 0x32},
+	/* 1 measurements per second */
+	{0x21, 0x30},
+	/* 2 measurements per second */
+	{0x22, 0x36},
+	/* 4 measurements per second */
+	{0x23, 0x34},
+	/* 10 measurements per second */
+	{0x27, 0x37},
+};
+
+/* periodic measure commands (low power mode) */
+static const char periodic_measure_commands_lpm[][SHT3X_CMD_LENGTH] = {
+	/* 0.5 measurements per second */
+	{0x20, 0x2f},
+	/* 1 measurements per second */
+	{0x21, 0x2d},
+	/* 2 measurements per second */
+	{0x22, 0x2b},
+	/* 4 measurements per second */
+	{0x23, 0x29},
+	/* 10 measurements per second */
+	{0x27, 0x2a},
+};
+
+struct sht3x_limit_commands {
+	const char read_command[SHT3X_CMD_LENGTH];
+	const char write_command[SHT3X_CMD_LENGTH];
+};
+
+static const struct sht3x_limit_commands limit_commands[] = {
+	/* temp1_max, humidity1_max */
+	[limit_max] = { {0xe1, 0x1f}, {0x61, 0x1d} },
+	/* temp_1_max_hyst, humidity1_max_hyst */
+	[limit_max_hyst] = { {0xe1, 0x14}, {0x61, 0x16} },
+	/* temp1_min, humidity1_min */
+	[limit_min] = { {0xe1, 0x02}, {0x61, 0x00} },
+	/* temp_1_min_hyst, humidity1_min_hyst */
+	[limit_min_hyst] = { {0xe1, 0x09}, {0x61, 0x0B} },
+};
+
+#define SHT3X_NUM_LIMIT_CMD  ARRAY_SIZE(limit_commands)
+
+static const u16 mode_to_update_interval[] = {
+	   0,
+	2000,
+	1000,
+	 500,
+	 250,
+	 100,
+};
+
+struct sht3x_data {
+	struct i2c_client *client;
+	struct mutex i2c_lock; /* lock for sending i2c commands */
+	struct mutex data_lock; /* lock for updating driver data */
+
+	u8 mode;
+	const unsigned char *command;
+	u32 wait_time;			/* in us*/
+	unsigned long last_update;	/* last update in periodic mode*/
+
+	struct sht3x_platform_data setup;
+
+	/*
+	 * cached values for temperature and humidity and limits
+	 * the limits arrays have the following order:
+	 * max, max_hyst, min, min_hyst
+	 */
+	int temperature;
+	int temperature_limits[SHT3X_NUM_LIMIT_CMD];
+	u32 humidity;
+	u32 humidity_limits[SHT3X_NUM_LIMIT_CMD];
+};
+
+static u8 get_mode_from_update_interval(u16 value)
+{
+	size_t index;
+	u8 number_of_modes = ARRAY_SIZE(mode_to_update_interval);
+
+	if (value == 0)
+		return 0;
+
+	/* find next faster update interval */
+	for (index = 1; index < number_of_modes; index++) {
+		if (mode_to_update_interval[index] <= value)
+			return index;
+	}
+
+	return number_of_modes - 1;
+}
+
+static int sht3x_read_from_command(struct i2c_client *client,
+				   struct sht3x_data *data,
+				   const char *command,
+				   char *buf, int length, u32 wait_time)
+{
+	int ret;
+
+	mutex_lock(&data->i2c_lock);
+	ret = i2c_master_send(client, command, SHT3X_CMD_LENGTH);
+
+	if (ret != SHT3X_CMD_LENGTH) {
+		ret = ret < 0 ? ret : -EIO;
+		goto out;
+	}
+
+	if (wait_time)
+		usleep_range(wait_time, wait_time + 1000);
+
+	ret = i2c_master_recv(client, buf, length);
+	if (ret != length) {
+		ret = ret < 0 ? ret : -EIO;
+		goto out;
+	}
+
+	ret = 0;
+out:
+	mutex_unlock(&data->i2c_lock);
+	return ret;
+}
+
+static int sht3x_extract_temperature(u16 raw)
+{
+	/*
+	 * From datasheet:
+	 * T = -45 + 175 * ST / 2^16
+	 * Adapted for integer fixed point (3 digit) arithmetic.
+	 */
+	return ((21875 * (int)raw) >> 13) - 45000;
+}
+
+static u32 sht3x_extract_humidity(u16 raw)
+{
+	/*
+	 * From datasheet:
+	 * RH = 100 * SRH / 2^16
+	 * Adapted for integer fixed point (3 digit) arithmetic.
+	 */
+	return (12500 * (u32)raw) >> 13;
+}
+
+static struct sht3x_data *sht3x_update_client(struct device *dev)
+{
+	struct sht3x_data *data = dev_get_drvdata(dev);
+	struct i2c_client *client = data->client;
+	u16 interval_ms = mode_to_update_interval[data->mode];
+	unsigned long interval_jiffies = msecs_to_jiffies(interval_ms);
+	unsigned char buf[SHT3X_RESPONSE_LENGTH];
+	u16 val;
+	int ret = 0;
+
+	mutex_lock(&data->data_lock);
+	/*
+	 * Only update cached readings once per update interval in periodic
+	 * mode. In single shot mode the sensor measures values on demand, so
+	 * every time the sysfs interface is called, a measurement is triggered.
+	 * In periodic mode however, the measurement process is handled
+	 * internally by the sensor and reading out sensor values only makes
+	 * sense if a new reading is available.
+	 */
+	if (time_after(jiffies, data->last_update + interval_jiffies)) {
+		ret = sht3x_read_from_command(client, data, data->command, buf,
+					      sizeof(buf), data->wait_time);
+		if (ret)
+			goto out;
+
+		val = be16_to_cpup((__be16 *)buf);
+		data->temperature = sht3x_extract_temperature(val);
+		val = be16_to_cpup((__be16 *)(buf + 3));
+		data->humidity = sht3x_extract_humidity(val);
+		data->last_update = jiffies;
+	}
+
+out:
+	mutex_unlock(&data->data_lock);
+	if (ret)
+		return ERR_PTR(ret);
+
+	return data;
+}
+
+/* sysfs attributes */
+static ssize_t temp1_input_show(struct device *dev,
+				struct device_attribute *attr, char *buf)
+{
+	struct sht3x_data *data = sht3x_update_client(dev);
+
+	if (IS_ERR(data))
+		return PTR_ERR(data);
+
+	return sprintf(buf, "%d\n", data->temperature);
+}
+
+static ssize_t humidity1_input_show(struct device *dev,
+				    struct device_attribute *attr, char *buf)
+{
+	struct sht3x_data *data = sht3x_update_client(dev);
+
+	if (IS_ERR(data))
+		return PTR_ERR(data);
+
+	return sprintf(buf, "%u\n", data->humidity);
+}
+
+/*
+ * limits_update must only be called from probe or with data_lock held
+ */
+static int limits_update(struct sht3x_data *data)
+{
+	int ret;
+	u8 index;
+	int temperature;
+	u32 humidity;
+	u16 raw;
+	char buffer[SHT3X_RESPONSE_LENGTH];
+	const struct sht3x_limit_commands *commands;
+	struct i2c_client *client = data->client;
+
+	for (index = 0; index < SHT3X_NUM_LIMIT_CMD; index++) {
+		commands = &limit_commands[index];
+		ret = sht3x_read_from_command(client, data,
+					      commands->read_command, buffer,
+					      SHT3X_RESPONSE_LENGTH, 0);
+
+		if (ret)
+			return ret;
+
+		raw = be16_to_cpup((__be16 *)buffer);
+		temperature = sht3x_extract_temperature((raw & 0x01ff) << 7);
+		humidity = sht3x_extract_humidity(raw & 0xfe00);
+		data->temperature_limits[index] = temperature;
+		data->humidity_limits[index] = humidity;
+	}
+
+	return ret;
+}
+
+static ssize_t temp1_limit_show(struct device *dev,
+				struct device_attribute *attr,
+				char *buf)
+{
+	struct sht3x_data *data = dev_get_drvdata(dev);
+	u8 index = to_sensor_dev_attr(attr)->index;
+	int temperature_limit = data->temperature_limits[index];
+
+	return scnprintf(buf, PAGE_SIZE, "%d\n", temperature_limit);
+}
+
+static ssize_t humidity1_limit_show(struct device *dev,
+				    struct device_attribute *attr,
+				    char *buf)
+{
+	struct sht3x_data *data = dev_get_drvdata(dev);
+	u8 index = to_sensor_dev_attr(attr)->index;
+	u32 humidity_limit = data->humidity_limits[index];
+
+	return scnprintf(buf, PAGE_SIZE, "%u\n", humidity_limit);
+}
+
+/*
+ * limit_store must only be called with data_lock held
+ */
+static size_t limit_store(struct device *dev,
+			  size_t count,
+			  u8 index,
+			  int temperature,
+			  u32 humidity)
+{
+	char buffer[SHT3X_CMD_LENGTH + SHT3X_WORD_LEN + SHT3X_CRC8_LEN];
+	char *position = buffer;
+	int ret;
+	u16 raw;
+	struct sht3x_data *data = dev_get_drvdata(dev);
+	struct i2c_client *client = data->client;
+	const struct sht3x_limit_commands *commands;
+
+	commands = &limit_commands[index];
+
+	memcpy(position, commands->write_command, SHT3X_CMD_LENGTH);
+	position += SHT3X_CMD_LENGTH;
+	/*
+	 * ST = (T + 45) / 175 * 2^16
+	 * SRH = RH / 100 * 2^16
+	 * adapted for fixed point arithmetic and packed the same as
+	 * in limit_show()
+	 */
+	raw = ((u32)(temperature + 45000) * 24543) >> (16 + 7);
+	raw |= ((humidity * 42950) >> 16) & 0xfe00;
+
+	*((__be16 *)position) = cpu_to_be16(raw);
+	position += SHT3X_WORD_LEN;
+	*position = crc8(sht3x_crc8_table,
+			 position - SHT3X_WORD_LEN,
+			 SHT3X_WORD_LEN,
+			 SHT3X_CRC8_INIT);
+
+	mutex_lock(&data->i2c_lock);
+	ret = i2c_master_send(client, buffer, sizeof(buffer));
+	mutex_unlock(&data->i2c_lock);
+
+	if (ret != sizeof(buffer))
+		return ret < 0 ? ret : -EIO;
+
+	data->temperature_limits[index] = temperature;
+	data->humidity_limits[index] = humidity;
+	return count;
+}
+
+static ssize_t temp1_limit_store(struct device *dev,
+				 struct device_attribute *attr,
+				 const char *buf,
+				 size_t count)
+{
+	int temperature;
+	int ret;
+	struct sht3x_data *data = dev_get_drvdata(dev);
+	u8 index = to_sensor_dev_attr(attr)->index;
+
+	ret = kstrtoint(buf, 0, &temperature);
+	if (ret)
+		return ret;
+
+	temperature = clamp_val(temperature, SHT3X_MIN_TEMPERATURE,
+				SHT3X_MAX_TEMPERATURE);
+	mutex_lock(&data->data_lock);
+	ret = limit_store(dev, count, index, temperature,
+			  data->humidity_limits[index]);
+	mutex_unlock(&data->data_lock);
+
+	return ret;
+}
+
+static ssize_t humidity1_limit_store(struct device *dev,
+				     struct device_attribute *attr,
+				     const char *buf,
+				     size_t count)
+{
+	u32 humidity;
+	int ret;
+	struct sht3x_data *data = dev_get_drvdata(dev);
+	u8 index = to_sensor_dev_attr(attr)->index;
+
+	ret = kstrtou32(buf, 0, &humidity);
+	if (ret)
+		return ret;
+
+	humidity = clamp_val(humidity, SHT3X_MIN_HUMIDITY, SHT3X_MAX_HUMIDITY);
+	mutex_lock(&data->data_lock);
+	ret = limit_store(dev, count, index, data->temperature_limits[index],
+			  humidity);
+	mutex_unlock(&data->data_lock);
+
+	return ret;
+}
+
+static void sht3x_select_command(struct sht3x_data *data)
+{
+	/*
+	 * In blocking mode (clock stretching mode) the I2C bus
+	 * is blocked for other traffic, thus the call to i2c_master_recv()
+	 * will wait until the data is ready. For non blocking mode, we
+	 * have to wait ourselves.
+	 */
+	if (data->mode > 0) {
+		data->command = sht3x_cmd_measure_periodic_mode;
+		data->wait_time = 0;
+	} else if (data->setup.blocking_io) {
+		data->command = data->setup.high_precision ?
+				sht3x_cmd_measure_blocking_hpm :
+				sht3x_cmd_measure_blocking_lpm;
+		data->wait_time = 0;
+	} else {
+		if (data->setup.high_precision) {
+			data->command = sht3x_cmd_measure_nonblocking_hpm;
+			data->wait_time = SHT3X_NONBLOCKING_WAIT_TIME_HPM;
+		} else {
+			data->command = sht3x_cmd_measure_nonblocking_lpm;
+			data->wait_time = SHT3X_NONBLOCKING_WAIT_TIME_LPM;
+		}
+	}
+}
+
+static int status_register_read(struct device *dev,
+				struct device_attribute *attr,
+				char *buffer, int length)
+{
+	int ret;
+	struct sht3x_data *data = dev_get_drvdata(dev);
+	struct i2c_client *client = data->client;
+
+	ret = sht3x_read_from_command(client, data, sht3x_cmd_read_status_reg,
+				      buffer, length, 0);
+
+	return ret;
+}
+
+static ssize_t temp1_alarm_show(struct device *dev,
+				struct device_attribute *attr,
+				char *buf)
+{
+	char buffer[SHT3X_WORD_LEN + SHT3X_CRC8_LEN];
+	int ret;
+
+	ret = status_register_read(dev, attr, buffer,
+				   SHT3X_WORD_LEN + SHT3X_CRC8_LEN);
+	if (ret)
+		return ret;
+
+	return scnprintf(buf, PAGE_SIZE, "%d\n", !!(buffer[0] & 0x04));
+}
+
+static ssize_t humidity1_alarm_show(struct device *dev,
+				    struct device_attribute *attr,
+				    char *buf)
+{
+	char buffer[SHT3X_WORD_LEN + SHT3X_CRC8_LEN];
+	int ret;
+
+	ret = status_register_read(dev, attr, buffer,
+				   SHT3X_WORD_LEN + SHT3X_CRC8_LEN);
+	if (ret)
+		return ret;
+
+	return scnprintf(buf, PAGE_SIZE, "%d\n", !!(buffer[0] & 0x08));
+}
+
+static ssize_t update_interval_show(struct device *dev,
+				    struct device_attribute *attr,
+				    char *buf)
+{
+	struct sht3x_data *data = dev_get_drvdata(dev);
+
+	return scnprintf(buf, PAGE_SIZE, "%u\n",
+			 mode_to_update_interval[data->mode]);
+}
+
+static ssize_t update_interval_store(struct device *dev,
+				     struct device_attribute *attr,
+				     const char *buf,
+				     size_t count)
+{
+	u16 update_interval;
+	u8 mode;
+	int ret;
+	const char *command;
+	struct sht3x_data *data = dev_get_drvdata(dev);
+	struct i2c_client *client = data->client;
+
+	ret = kstrtou16(buf, 0, &update_interval);
+	if (ret)
+		return ret;
+
+	mode = get_mode_from_update_interval(update_interval);
+
+	mutex_lock(&data->data_lock);
+	/* mode did not change */
+	if (mode == data->mode) {
+		mutex_unlock(&data->data_lock);
+		return count;
+	}
+
+	mutex_lock(&data->i2c_lock);
+	/*
+	 * Abort periodic measure mode.
+	 * To do any changes to the configuration while in periodic mode, we
+	 * have to send a break command to the sensor, which then falls back
+	 * to single shot (mode = 0).
+	 */
+	if (data->mode > 0) {
+		ret = i2c_master_send(client, sht3x_cmd_break,
+				      SHT3X_CMD_LENGTH);
+		if (ret != SHT3X_CMD_LENGTH)
+			goto out;
+		data->mode = 0;
+	}
+
+	if (mode > 0) {
+		if (data->setup.high_precision)
+			command = periodic_measure_commands_hpm[mode - 1];
+		else
+			command = periodic_measure_commands_lpm[mode - 1];
+
+		/* select mode */
+		ret = i2c_master_send(client, command, SHT3X_CMD_LENGTH);
+		if (ret != SHT3X_CMD_LENGTH)
+			goto out;
+	}
+
+	/* select mode and command */
+	data->mode = mode;
+	sht3x_select_command(data);
+
+out:
+	mutex_unlock(&data->i2c_lock);
+	mutex_unlock(&data->data_lock);
+	if (ret != SHT3X_CMD_LENGTH)
+		return ret < 0 ? ret : -EIO;
+
+	return count;
+}
+
+static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO, temp1_input_show, NULL, 0);
+static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO, humidity1_input_show,
+			  NULL, 0);
+static SENSOR_DEVICE_ATTR(temp1_max, S_IRUGO | S_IWUSR,
+			  temp1_limit_show, temp1_limit_store,
+			  limit_max);
+static SENSOR_DEVICE_ATTR(humidity1_max, S_IRUGO | S_IWUSR,
+			  humidity1_limit_show, humidity1_limit_store,
+			  limit_max);
+static SENSOR_DEVICE_ATTR(temp1_max_hyst, S_IRUGO | S_IWUSR,
+			  temp1_limit_show, temp1_limit_store,
+			  limit_max_hyst);
+static SENSOR_DEVICE_ATTR(humidity1_max_hyst, S_IRUGO | S_IWUSR,
+			  humidity1_limit_show, humidity1_limit_store,
+			  limit_max_hyst);
+static SENSOR_DEVICE_ATTR(temp1_min, S_IRUGO | S_IWUSR,
+			  temp1_limit_show, temp1_limit_store,
+			  limit_min);
+static SENSOR_DEVICE_ATTR(humidity1_min, S_IRUGO | S_IWUSR,
+			  humidity1_limit_show, humidity1_limit_store,
+			  limit_min);
+static SENSOR_DEVICE_ATTR(temp1_min_hyst, S_IRUGO | S_IWUSR,
+			  temp1_limit_show, temp1_limit_store,
+			  limit_min_hyst);
+static SENSOR_DEVICE_ATTR(humidity1_min_hyst, S_IRUGO | S_IWUSR,
+			  humidity1_limit_show, humidity1_limit_store,
+			  limit_min_hyst);
+static SENSOR_DEVICE_ATTR(temp1_alarm, S_IRUGO, temp1_alarm_show, NULL, 0);
+static SENSOR_DEVICE_ATTR(humidity1_alarm, S_IRUGO, humidity1_alarm_show,
+			  NULL, 0);
+static SENSOR_DEVICE_ATTR(update_interval, S_IRUGO | S_IWUSR,
+			  update_interval_show, update_interval_store, 0);
+
+static struct attribute *sht3x_attrs[] = {
+	&sensor_dev_attr_temp1_input.dev_attr.attr,
+	&sensor_dev_attr_humidity1_input.dev_attr.attr,
+	&sensor_dev_attr_temp1_max.dev_attr.attr,
+	&sensor_dev_attr_temp1_max_hyst.dev_attr.attr,
+	&sensor_dev_attr_humidity1_max.dev_attr.attr,
+	&sensor_dev_attr_humidity1_max_hyst.dev_attr.attr,
+	&sensor_dev_attr_temp1_min.dev_attr.attr,
+	&sensor_dev_attr_temp1_min_hyst.dev_attr.attr,
+	&sensor_dev_attr_humidity1_min.dev_attr.attr,
+	&sensor_dev_attr_humidity1_min_hyst.dev_attr.attr,
+	&sensor_dev_attr_temp1_alarm.dev_attr.attr,
+	&sensor_dev_attr_humidity1_alarm.dev_attr.attr,
+	&sensor_dev_attr_update_interval.dev_attr.attr,
+	NULL
+};
+
+static struct attribute *sts3x_attrs[] = {
+	&sensor_dev_attr_temp1_input.dev_attr.attr,
+	NULL
+};
+
+ATTRIBUTE_GROUPS(sht3x);
+ATTRIBUTE_GROUPS(sts3x);
+
+static int sht3x_probe(struct i2c_client *client,
+		       const struct i2c_device_id *id)
+{
+	int ret;
+	struct sht3x_data *data;
+	struct device *hwmon_dev;
+	struct i2c_adapter *adap = client->adapter;
+	struct device *dev = &client->dev;
+	const struct attribute_group **attribute_groups;
+
+	/*
+	 * we require full i2c support since the sht3x uses multi-byte read and
+	 * writes as well as multi-byte commands which are not supported by
+	 * the smbus protocol
+	 */
+	if (!i2c_check_functionality(adap, I2C_FUNC_I2C))
+		return -ENODEV;
+
+	ret = i2c_master_send(client, sht3x_cmd_clear_status_reg,
+			      SHT3X_CMD_LENGTH);
+	if (ret != SHT3X_CMD_LENGTH)
+		return ret < 0 ? ret : -ENODEV;
+
+	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->setup.blocking_io = false;
+	data->setup.high_precision = true;
+	data->mode = 0;
+	data->last_update = 0;
+	data->client = client;
+	crc8_populate_msb(sht3x_crc8_table, SHT3X_CRC8_POLYNOMIAL);
+
+	if (client->dev.platform_data)
+		data->setup = *(struct sht3x_platform_data *)dev->platform_data;
+
+	sht3x_select_command(data);
+
+	mutex_init(&data->i2c_lock);
+	mutex_init(&data->data_lock);
+
+	ret = limits_update(data);
+	if (ret)
+		return ret;
+
+	if (id->driver_data == sts3x)
+		attribute_groups = sts3x_groups;
+	else
+		attribute_groups = sht3x_groups;
+
+	hwmon_dev = devm_hwmon_device_register_with_groups(dev,
+							   client->name,
+							   data,
+							   attribute_groups);
+
+	if (IS_ERR(hwmon_dev))
+		dev_dbg(dev, "unable to register hwmon device\n");
+
+	return PTR_ERR_OR_ZERO(hwmon_dev);
+}
+
+/* device ID table */
+static const struct i2c_device_id sht3x_ids[] = {
+	{"sht3x", sht3x},
+	{"sts3x", sts3x},
+	{}
+};
+
+MODULE_DEVICE_TABLE(i2c, sht3x_ids);
+
+static struct i2c_driver sht3x_i2c_driver = {
+	.driver.name = "sht3x",
+	.probe       = sht3x_probe,
+	.id_table    = sht3x_ids,
+};
+
+module_i2c_driver(sht3x_i2c_driver);
+
+MODULE_AUTHOR("David Frey <david.frey@sensirion.com>");
+MODULE_AUTHOR("Pascal Sachs <pascal.sachs@sensirion.com>");
+MODULE_DESCRIPTION("Sensirion SHT3x humidity and temperature sensor driver");
+MODULE_LICENSE("GPL");
diff --git a/include/linux/platform_data/sht3x.h b/include/linux/platform_data/sht3x.h
new file mode 100644
index 000000000000..2e5eea358194
--- /dev/null
+++ b/include/linux/platform_data/sht3x.h
@@ -0,0 +1,25 @@
+/*
+ * Copyright (C) 2016 Sensirion AG, Switzerland
+ * Author: David Frey <david.frey@sensirion.com>
+ * Author: Pascal Sachs <pascal.sachs@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.
+ *
+ */
+
+#ifndef __SHT3X_H_
+#define __SHT3X_H_
+
+struct sht3x_platform_data {
+	bool blocking_io;
+	bool high_precision;
+};
+#endif /* __SHT3X_H_ */