media: dt-bindings: video-interfaces: Document 'orientation' property

Add the 'orientation' device property, used to specify the device mounting
position. The property is particularly meaningful for mobile devices
with a well defined usage orientation.
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Tomasz Figa <tfiga@chromium.org>
Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Documentation/devicetree/bindings/media/video-interfaces.txt

@@ -89,6 +89,17 @@ Optional properties
   but a number of degrees counter clockwise. Typical values are 0 and 180
   (upside down).
 
+- orientation: The orientation of a device (typically an image sensor or a flash
+  LED) describing its mounting position relative to the usage orientation of the
+  system where the device is installed on.
+  Possible values are:
+  0 - Front. The device is mounted on the front facing side of the system.
+  For mobile devices such as smartphones, tablets and laptops the front side is
+  the user facing side.
+  1 - Back. The device is mounted on the back side of the system, which is
+  defined as the opposite side of the front facing one.
+  2 - External. The device is not attached directly to the system but is
+  attached in a way that allows it to move freely.
 
 Optional endpoint properties
 ----------------------------