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_ */