[RFC 3/7] media: uapi: v4l: Document source routes

[Sakari Ailus <sakari.ailus@linux.intel.com>]

Document how internal pads are used on source routes.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
---
 .../userspace-api/media/v4l/dev-subdev.rst     | 18 ++++++++++++++++++
 .../media/v4l/vidioc-subdev-g-routing.rst      |  5 +++++
 include/uapi/linux/v4l2-subdev.h               |  6 +++++-
 3 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/Documentation/userspace-api/media/v4l/dev-subdev.rst b/Documentation/userspace-api/media/v4l/dev-subdev.rst
index a4f1df7093e8..395e06d2f0f2 100644
--- a/Documentation/userspace-api/media/v4l/dev-subdev.rst
+++ b/Documentation/userspace-api/media/v4l/dev-subdev.rst
@@ -551,6 +551,24 @@ A stream at a specific point in the media pipeline is identified by the
 sub-device and a (pad, stream) pair. For sub-devices that do not support
 multiplexed streams the 'stream' field is always 0.
 
+.. _v4l2-subdev-source-routes:
+
+Source routes
+^^^^^^^^^^^^^
+
+Cases where a single sub-device pad is a source of multiple streams are special
+as there is no sink pad for such a route. In those cases, an internal pad is
+used as the sink pad. Such pads have the :ref:`MEDIA_PAD_FL_INTERNAL_SOURCE
+<MEDIA-PAD-FL-INTERNAL-SOURCE>` flag set.
+
+Internal pads have all the properties of a sink pad in such case, including
+formats and selections. The format in this case is the source format of the
+stream. An internal pad always has a single stream only (0).
+
+Generally source routes are not modifiable but they can be activated and
+inactivated using the :ref:`V4L2_SUBDEV_ROUTE_FL_ACTIVE
+<v4l2-subdev-routing-flags>` flag, depending on driver capabilities.
+
 Interaction between routes, streams, formats and selections
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
diff --git a/Documentation/userspace-api/media/v4l/vidioc-subdev-g-routing.rst b/Documentation/userspace-api/media/v4l/vidioc-subdev-g-routing.rst
index 68ca343c3b44..e00622071b64 100644
--- a/Documentation/userspace-api/media/v4l/vidioc-subdev-g-routing.rst
+++ b/Documentation/userspace-api/media/v4l/vidioc-subdev-g-routing.rst
@@ -94,6 +94,11 @@ for all the route entries and call ``VIDIOC_SUBDEV_G_ROUTING`` again.
     * - __u32
       - ``sink_pad``
       - Sink pad number.
+    * - __u32
+      - ``internal_source_pad``
+      - Internal source pad number. For pads with :ref:`internal source pad flag
+	<MEDIA-PAD-FL-INTERNAL-SOURCE>`, for use with :ref:`source routes
+	<v4l2-subdev-source-routes>`.
     * - __u32
       - ``sink_stream``
       - Sink pad stream number.
diff --git a/include/uapi/linux/v4l2-subdev.h b/include/uapi/linux/v4l2-subdev.h
index 4a195b68f28f..703e3a1f199b 100644
--- a/include/uapi/linux/v4l2-subdev.h
+++ b/include/uapi/linux/v4l2-subdev.h
@@ -203,6 +203,7 @@ struct v4l2_subdev_capability {
  * struct v4l2_subdev_route - A route inside a subdev
  *
  * @sink_pad: the sink pad index
+ * @internal_source_pad: the internal source pad
  * @sink_stream: the sink stream identifier
  * @source_pad: the source pad index
  * @source_stream: the source stream identifier
@@ -210,7 +211,10 @@ struct v4l2_subdev_capability {
  * @reserved: drivers and applications must zero this array
  */
 struct v4l2_subdev_route {
-	__u32 sink_pad;
+	union {
+		__u32 sink_pad;
+		__u32 internal_source_pad;
+	};
 	__u32 sink_stream;
 	__u32 source_pad;
 	__u32 source_stream;
-- 
2.30.2