[PATCH v3 7/7] media: open.rst: add a notice about subdev-API on vdev-centric

[Mauro Carvalho Chehab <mchehab@s-opensource.com>]

The documentation doesn't mention if vdev-centric hardware
control would have subdev API or not.

Add a notice about that, reflecting the current status, where
three drivers use it, in order to support some subdev-specific
controls.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
---
 Documentation/media/uapi/v4l/open.rst | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst
index 3257a0527ac9..547d191dcef2 100644
--- a/Documentation/media/uapi/v4l/open.rst
+++ b/Documentation/media/uapi/v4l/open.rst
@@ -43,6 +43,13 @@ the application to know with device nodes are available
 For **MC-centric** hardware peripheral control, before using the
 peripheral, it is required to set the pipelines via the
 
+.. note::
+
+   A **vdev-centric** may optionally expose V4L2 sub-devices via
+   :ref:`sub-device API <subdev>`. In that case, it has to implement
+   the :ref:`media controller API <media_controller>` as well.
+
+
 :ref:`media controller API <media_controller>`. For those devices, the
 sub-devices' configuration can be controlled via the
 :ref:`sub-device API <subdev>`, whith creates one device node
-- 
2.13.3