iio: Add support for humidity sensors

There are already humidity sensors in the hwmon subsystem,
so we use their unit (milli percent) here as well.
Signed-off-by: Harald Geyer <harald@ccbib.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Documentation/ABI/testing/sysfs-bus-iio

@@ -197,6 +197,19 @@ Description:
 		Raw pressure measurement from channel Y. Units after
 		application of scale and offset are kilopascal.
 
+What:		/sys/bus/iio/devices/iio:deviceX/in_humidityrelative_raw
+KernelVersion:	3.14
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Raw humidity measurement of air. Units after application of
+		scale and offset are milli percent.
+
+What:		/sys/bus/iio/devices/iio:deviceX/in_humidityrelative_input
+KernelVersion:	3.14
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Scaled humidity measurement in milli percent.
+
 What:		/sys/bus/iio/devices/iio:deviceX/in_accel_offset
 What:		/sys/bus/iio/devices/iio:deviceX/in_accel_x_offset
 What:		/sys/bus/iio/devices/iio:deviceX/in_accel_y_offset

drivers/iio/industrialio-core.c

@@ -69,6 +69,7 @@ static const char * const iio_chan_type_name_spec[] = {
 	[IIO_ALTVOLTAGE] = "altvoltage",
 	[IIO_CCT] = "cct",
 	[IIO_PRESSURE] = "pressure",
+	[IIO_HUMIDITYRELATIVE] = "humidityrelative",
 };
 
 static const char * const iio_modifier_names[] = {

include/linux/iio/types.h

@@ -29,6 +29,7 @@ enum iio_chan_type {
 	IIO_ALTVOLTAGE,
 	IIO_CCT,
 	IIO_PRESSURE,
+	IIO_HUMIDITYRELATIVE,
 };
 
 enum iio_modifier {