iio: core: Introduce IIO_CHAN_INFO_CALIBEMISSIVITY

Contact-less IR temperature sensors measure the temperature of an object
by using its thermal radiation.  Surfaces with different emissivity
ratios emit different amounts of energy at the same temperature.

IIO_CHAN_INFO_CALIBEMISSIVITY allows the user to inform the sensor of the
emissivity of the object in front of it, in order to effectively measure
its temperature.

A device providing such setting is Melexis's MLX90614:
http://melexis.com/Assets/IR-sensor-thermometer-MLX90614-Datasheet-5152.aspx.
Signed-off-by: NVianney le Clément de Saint-Marcq <vianney.leclement@essensium.com>
Cc: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: NJonathan Cameron <jic23@kernel.org>

Documentation/ABI/testing/sysfs-bus-iio

@@ -1364,3 +1364,14 @@ Description:
 		hwfifo_watermak_min but not equal to any of the values in this
 		list, the driver will chose an appropriate value for the
 		hardware fifo watermark level.
+
+What:		/sys/bus/iio/devices/iio:deviceX/in_temp_calibemissivity
+What:		/sys/bus/iio/devices/iio:deviceX/in_tempX_calibemissivity
+What:		/sys/bus/iio/devices/iio:deviceX/in_temp_object_calibemissivity
+What:		/sys/bus/iio/devices/iio:deviceX/in_tempX_object_calibemissivity
+KernelVersion:	4.1
+Contact:	linux-iio@vger.kernel.org
+Description:
+		The emissivity ratio of the surface in the field of view of the
+		contactless temperature sensor.  Emissivity varies from 0 to 1,
+		with 1 being the emissivity of a black body.

drivers/iio/industrialio-core.c

@@ -128,6 +128,7 @@ static const char * const iio_chan_info_postfix[] = {
 	[IIO_CHAN_INFO_CALIBWEIGHT] = "calibweight",
 	[IIO_CHAN_INFO_DEBOUNCE_COUNT] = "debounce_count",
 	[IIO_CHAN_INFO_DEBOUNCE_TIME] = "debounce_time",
+	[IIO_CHAN_INFO_CALIBEMISSIVITY] = "calibemissivity",
 };
 
 /**

include/linux/iio/iio.h

@@ -43,6 +43,7 @@ enum iio_chan_info_enum {
 	IIO_CHAN_INFO_CALIBWEIGHT,
 	IIO_CHAN_INFO_DEBOUNCE_COUNT,
 	IIO_CHAN_INFO_DEBOUNCE_TIME,
+	IIO_CHAN_INFO_CALIBEMISSIVITY,
 };
 
 enum iio_shared_by {