[PATCH v12 37/86] media: Documentation: Add sub-device internal pads example

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

Add an example using sub-device internal pads, with the Sony IMX219 camera
sensor.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
---
 .../userspace-api/media/v4l/dev-subdev.rst    | 129 ++++++++++++++++++
 1 file changed, 129 insertions(+)

diff --git a/Documentation/userspace-api/media/v4l/dev-subdev.rst b/Documentation/userspace-api/media/v4l/dev-subdev.rst
index 2fc81e0205dc..a9d462b57b54 100644
--- a/Documentation/userspace-api/media/v4l/dev-subdev.rst
+++ b/Documentation/userspace-api/media/v4l/dev-subdev.rst
@@ -729,4 +729,133 @@ To configure this pipeline, the userspace must take the following steps:
    controls are present on the source sub-device to obtain the pixel array CFA
    pattern and metadata layout.
 
+Internal pads setup example
+---------------------------
+
+A simple example of a multiplexed stream setup might be as follows:
+
+- An IMX219 camera sensor source sub-device, with one source pad (0), one
+  internal sink pad (1) as the source of the image data and an internal sink
+  pad (2) as the source of the embedded data. There are two routes, one from the
+  internal sink pad 1 to the source pad 0 (image data) and another from the
+  internal sink pad 2 to the source pad 0 (embedded data). Both streams are
+  always active, i.e. there is no need to separately enable the embedded data
+  stream. The sensor uses the CSI-2 interface.
+
+- A CSI-2 receiver in the SoC. The receiver has a single sink pad (pad 0),
+  connected to the sensor's source pad (0), and two source pads (pads 1 and 2),
+  to two DMA engines. The receiver demultiplexes the incoming streams to the
+  source pads.
+
+- Two DMA engines in the SoC, one for each stream. Each DMA engine is connected
+  to a different source pad of the receiver.
+
+The sensor and the receiver are modelled as V4L2 sub-devices, exposed to
+userspace via /dev/v4l-subdevX device nodes. The DMA engines are modelled as
+V4L2 video devices, exposed to userspace via /dev/videoX nodes.
+
+To configure this pipeline, the userspace must take the following steps:
+
+1) Set up media links between entities: enable the links from the sensor to the
+   receiver and from the receiver to the DMA engines. This step does not differ
+   from normal non-multiplexed media controller setup.
+
+2) Configure routing
+
+.. flat-table:: Camera sensor. There are no configurable routes.
+    :header-rows: 1
+
+    * - Sink Pad/Stream
+      - Source Pad/Stream
+      - Routing Flags
+      - Comments
+    * - 1/0
+      - 0/0
+      - V4L2_SUBDEV_ROUTE_FL_ACTIVE | V4L2_SUBDEV_ROUTE_FL_IMMUTABLE |
+        V4L2_SUBDEV_ROUTE_FL_STATIC
+      - Pixel data stream from the internal image sink pad
+    * - 2/0
+      - 0/1
+      - V4L2_SUBDEV_ROUTE_FL_ACTIVE | V4L2_SUBDEV_ROUTE_FL_IMMUTABLE |
+        V4L2_SUBDEV_ROUTE_FL_STATIC
+      - Metadata stream from the internal embedded data sink pad
+
+While both routes are immutable for the IMX219, other camera sensors may offer
+more flexible configuration options. Routing configuration is dictated by the
+hardware capabilities: camera sensors typically always produce an image data
+stream, but some of them support enabling and disabling the embedded data
+stream.
+
+.. flat-table:: Receiver routing table. Typically both routes need to be
+		explicitly created.
+    :header-rows:  1
+
+    * - Sink Pad/Stream
+      - Source Pad/Stream
+      - Routing Flags
+      - Comments
+    * - 0/0
+      - 1/0
+      - V4L2_SUBDEV_ROUTE_FL_ACTIVE
+      - Pixel data stream from camera sensor
+    * - 0/1
+      - 2/0
+      - V4L2_SUBDEV_ROUTE_FL_ACTIVE
+      - Metadata stream from camera sensor
+
+3) Configure formats
+
+   This example assumes that the formats are propagated from sink pad to the
+   source pad as-is. The tables contain fields of both struct v4l2_subdev_format
+   and struct v4l2_mbus_framefmt.
+
+.. flat-table:: Formats set on the sub-devices. Bold values are set, others are
+                static or propagated. The order is aligned with configured
+                routes.
+    :header-rows: 1
+    :fill-cells:
+
+    * - Sub-device
+      - Pad/Stream
+      - Width
+      - Height
+      - Code
+    * - :rspan:`3` IMX219
+      - 1/0
+      - 3296
+      - 2480
+      - MEDIA_BUS_FMT_RAW_10
+    * - 0/0
+      - 3296
+      - 2480
+      - **MEDIA_BUS_FMT_RAW_10**
+    * - 2/0
+      - 3296
+      - 2
+      - MEDIA_BUS_FMT_META_10
+    * - 0/1
+      - 3296
+      - 2
+      - MEDIA_BUS_FMT_META_10
+    * - :rspan:`3` CSI-2 receiver
+      - 0/0
+      - **3296**
+      - **2480**
+      - **MEDIA_BUS_FMT_RAW_10**
+    * - 1/0
+      - 3296
+      - 2480
+      - MEDIA_BUS_FMT_RAW_10
+    * - 0/1
+      - **3296**
+      - **2**
+      - **MEDIA_BUS_FMT_META_10**
+    * - 2/0
+      - 3296
+      - 2
+      - MEDIA_BUS_FMT_META_10
+
+The embedded data format does not need to be configured on the sensor's pads as
+the format is dictated by the pixel data format in this case.
+
 .. include:: subdev-config-model.rst
-- 
2.47.3