iio: documentation: Document scd4x calibration use

Add entries from Documentation/ABI/testing/sysfs-bus-iio-scd30
to Documentation/ABI/testing/sysfs-bus-iio. The attributes of the scd4x
and scd30 are common.

Remove Documentation/ABI/testing/sysfs-bus-iio-scd30.

Signed-off-by: Roan van Dijk <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

Documentation/ABI/testing/sysfs-bus-iio

···
 		Specify the percent for light sensor relative to the channel
 		absolute value that a data field should change before an event
 		is generated. Units are a percentage of the prior reading.
+
+What:		/sys/bus/iio/devices/iio:deviceX/calibration_auto_enable
+Date:		June 2020
+KernelVersion:	5.8
+Contact:	[e-mail]
+Description:
+		Some sensors have the ability to apply auto calibration at
+		runtime. For example, it may be necessary to compensate for
+		contaminant build-up in a measurement chamber or optical
+		element deterioration that would otherwise lead to sensor drift.
+
+		Writing 1 or 0 to this attribute will respectively activate or
+		deactivate this auto calibration function.
+
+		Upon reading, the current status is returned.
+
+What:		/sys/bus/iio/devices/iio:deviceX/calibration_forced_value
+Date:		June 2020
+KernelVersion:	5.8
+Contact:	[e-mail]
+Description:
+		Some sensors have the ability to apply a manual calibration using
+		a known measurement value, perhaps obtained from an external
+		reference device.
+
+		Writing a value to this function will force such a calibration
+		change. For the scd30 the value should be from the range
+		[400 1 2000].
+
+		Note for the scd30 that a valid value may only be obtained once
+		it is has been written. Until then any read back of this value
+		should be ignored. As for the scd4x an error will be returned
+		immediately if the manual calibration has failed.
+
+What:		/sys/bus/iio/devices/iio:deviceX/calibration_forced_value_available
+KernelVersion:  5.15
+Contact:        [e-mail]
+Description:
+		Available range for the forced calibration value, expressed as:
+
+		- a range specified as "[min step max]"

Documentation/ABI/testing/sysfs-bus-iio-scd30

···
-What:		/sys/bus/iio/devices/iio:deviceX/calibration_auto_enable
-Date:		June 2020
-KernelVersion:	5.8
-Contact:	[e-mail]
-Description:
-		Contaminants build-up in the measurement chamber or optical
-		elements deterioration leads to sensor drift.
-
-		One can compensate for sensor drift by using automatic self
-		calibration procedure (asc).
-
-		Writing 1 or 0 to this attribute will respectively activate or
-		deactivate asc.
-
-		Upon reading current asc status is returned.
-
-What:		/sys/bus/iio/devices/iio:deviceX/calibration_forced_value
-Date:		June 2020
-KernelVersion:	5.8
-Contact:	[e-mail]
-Description:
-		Contaminants build-up in the measurement chamber or optical
-		elements deterioration leads to sensor drift.
-
-		One can compensate for sensor drift by using forced
-		recalibration (frc). This is useful in case there's known
-		co2 reference available nearby the sensor.
-
-		Picking value from the range [400 1 2000] and writing it to the
-		sensor will set frc.
-
-		Upon reading current frc value is returned. Note that after
-		power cycling default value (i.e 400) is returned even though
-		internally sensor had recalibrated itself.