iio: Add channel for Phase

Add new channel type support for phase.

This channel may be used by Time-of-flight sensors to express the
phase difference between emitted and received signals. Those sensor
will then use the phase shift of return signals to approximate the
distance to objects.

Signed-off-by: Mathieu Othacehe <[email protected]>
Signed-off-by: Jonathan Cameron <[email protected]>
diff --git a/Documentation/ABI/testing/sysfs-bus-iio b/Documentation/ABI/testing/sysfs-bus-iio
index c735303..c9cfa83 100644
--- a/Documentation/ABI/testing/sysfs-bus-iio
+++ b/Documentation/ABI/testing/sysfs-bus-iio
@@ -1675,3 +1675,10 @@
 Contact:	[email protected]
 Description:
 		Raw counter device counters direction for channel Y.
+
+What:		/sys/bus/iio/devices/iio:deviceX/in_phaseY_raw
+KernelVersion:	4.18
+Contact:	[email protected]
+Description:
+		Raw (unscaled) phase difference reading from channel Y
+		that can be processed to radians.
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