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 <[email protected]>
[groeck: Fixed 'Variable length array is used' gcc warning]
Signed-off-by: Guenter Roeck <[email protected]>

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 <[email protected]>
+  Pascal Sachs <[email protected]>
+
+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