media: vimc: documentation for lens

Add documentation for vimc-lens.
Add a lens into the vimc topology graph.

Signed-off-by: Yunke Cao <yunkec@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
diff --git a/Documentation/admin-guide/media/vimc.rst b/Documentation/admin-guide/media/vimc.rst
index 0b07f05..3b4d2b3 100644
--- a/Documentation/admin-guide/media/vimc.rst
+++ b/Documentation/admin-guide/media/vimc.rst
@@ -53,6 +53,25 @@
 
 	* 1 Pad source
 
+vimc-lens:
+	Ancillary lens for a sensor. Supports auto focus control. Linked to
+	a vimc-sensor using an ancillary link. The lens supports FOCUS_ABSOLUTE
+	control.
+
+.. code-block:: bash
+
+	media-ctl -p
+	...
+	- entity 28: Lens A (0 pad, 0 link)
+			type V4L2 subdev subtype Lens flags 0
+			device node name /dev/v4l-subdev6
+	- entity 29: Lens B (0 pad, 0 link)
+			type V4L2 subdev subtype Lens flags 0
+			device node name /dev/v4l-subdev7
+	v4l2-ctl -d /dev/v4l-subdev7 -C focus_absolute
+	focus_absolute: 0
+
+
 vimc-debayer:
 	Transforms images in bayer format into a non-bayer format.
 	Exposes: