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>

Documentation/hwmon/sht3x

+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

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

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

include/linux/platform_data/sht3x.h

+/*
+ * 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_ */