media: admin-guide: Add starfive_camss.rst for Starfive Camera Subsystem

Add starfive_camss.rst file that documents the Starfive Camera
Subsystem driver which is used for handing image sensor data.
Signed-off-by: Jack Zhu <jack.zhu@starfivetech.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>

Documentation/admin-guide/media/starfive_camss.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+.. include:: <isonum.txt>
+
+================================
+Starfive Camera Subsystem driver
+================================
+
+Introduction
+------------
+
+This file documents the driver for the Starfive Camera Subsystem found on
+Starfive JH7110 SoC. The driver is located under drivers/staging/media/starfive/
+camss.
+
+The driver implements V4L2, Media controller and v4l2_subdev interfaces. Camera
+sensor using V4L2 subdev interface in the kernel is supported.
+
+The driver has been successfully used on the Gstreamer 1.18.5 with v4l2src
+plugin.
+
+
+Starfive Camera Subsystem hardware
+----------------------------------
+
+The Starfive Camera Subsystem hardware consists of::
+
+                    |\         +---------------+      +-----------+
+  +----------+      |  \       |               |      |           |
+  |          |      |   |      |               |      |           |
+  |   MIPI   |----->|   |----->|      ISP      |----->|           |
+  |          |      |   |      |               |      |           |
+  +----------+      |   |      |               |      |  Memory   |
+                    |MUX|      +---------------+      | Interface |
+  +----------+      |   |                             |           |
+  |          |      |   |---------------------------->|           |
+  | Parallel |----->|   |                             |           |
+  |          |      |   |                             |           |
+  +----------+      |  /                              |           |
+                    |/                                +-----------+
+
+- MIPI: The MIPI interface, receiving data from a MIPI CSI-2 camera sensor.
+
+- Parallel: The parallel interface,  receiving data from a parallel sensor.
+
+- ISP: The ISP, processing raw Bayer data from an image sensor and producing
+  YUV frames.
+
+
+Topology
+--------
+
+The media controller pipeline graph is as follows:
+
+.. _starfive_camss_graph:
+
+.. kernel-figure:: starfive_camss_graph.dot
+    :alt:   starfive_camss_graph.dot
+    :align: center
+
+The driver has 2 video devices:
+
+- capture_raw: The capture device, capturing image data directly from a sensor.
+- capture_yuv: The capture device, capturing YUV frame data processed by the
+  ISP module
+
+The driver has 3 subdevices:
+
+- stf_isp: is responsible for all the isp operations, outputs YUV frames.
+- cdns_csi2rx: a CSI-2 bridge supporting up to 4 CSI lanes in input, and 4
+  different pixel streams in output.
+- imx219: an image sensor, image data is sent through MIPI CSI-2.

Documentation/admin-guide/media/starfive_camss_graph.dot

+digraph board {
+	rankdir=TB
+	n00000001 [label="{{<port0> 0} | stf_isp\n/dev/v4l-subdev0 | {<port1> 1}}", shape=Mrecord, style=filled, fillcolor=green]
+	n00000001:port1 -> n00000008 [style=dashed]
+	n00000004 [label="capture_raw\n/dev/video0", shape=box, style=filled, fillcolor=yellow]
+	n00000008 [label="capture_yuv\n/dev/video1", shape=box, style=filled, fillcolor=yellow]
+	n0000000e [label="{{<port0> 0} | cdns_csi2rx.19800000.csi-bridge\n | {<port1> 1 | <port2> 2 | <port3> 3 | <port4> 4}}", shape=Mrecord, style=filled, fillcolor=green]
+	n0000000e:port1 -> n00000001:port0 [style=dashed]
+	n0000000e:port1 -> n00000004 [style=dashed]
+	n00000018 [label="{{} | imx219 6-0010\n/dev/v4l-subdev1 | {<port0> 0}}", shape=Mrecord, style=filled, fillcolor=green]
+	n00000018:port0 -> n0000000e:port0 [style=bold]
+}

Documentation/admin-guide/media/v4l-drivers.rst

@@ -28,6 +28,7 @@ Video4Linux (V4L) driver-specific documentation
 	si470x
 	si4713
 	si476x
+	starfive_camss
 	vimc
 	visl
 	vivid

MAINTAINERS

@@ -20643,6 +20643,7 @@ M:	Jack Zhu <jack.zhu@starfivetech.com>
 M:	Changhuang Liang <changhuang.liang@starfivetech.com>
 L:	linux-media@vger.kernel.org
 S:	Maintained
+F:	Documentation/admin-guide/media/starfive_camss.rst
 F:	Documentation/devicetree/bindings/media/starfive,jh7110-camss.yaml
 
 STARFIVE CRYPTO DRIVER