[PATCH 4/4] media: admin-guide: Document the Raspberry Pi CFE (rp1-cfe)

[Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>]

Add documentation for rp1-cfe driver.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
---
 .../admin-guide/media/raspberrypi-rp1-cfe.dot      | 27 ++++++++
 .../admin-guide/media/raspberrypi-rp1-cfe.rst      | 78 ++++++++++++++++++++++
 Documentation/admin-guide/media/v4l-drivers.rst    |  1 +
 3 files changed, 106 insertions(+)

diff --git a/Documentation/admin-guide/media/raspberrypi-rp1-cfe.dot b/Documentation/admin-guide/media/raspberrypi-rp1-cfe.dot
new file mode 100644
index 000000000000..7717f2291049
--- /dev/null
+++ b/Documentation/admin-guide/media/raspberrypi-rp1-cfe.dot
@@ -0,0 +1,27 @@
+digraph board {
+	rankdir=TB
+	n00000001 [label="{{<port0> 0} | csi2\n/dev/v4l-subdev0 | {<port1> 1 | <port2> 2 | <port3> 3 | <port4> 4}}", shape=Mrecord, style=filled, fillcolor=green]
+	n00000001:port1 -> n00000011 [style=dashed]
+	n00000001:port1 -> n00000007:port0
+	n00000001:port2 -> n00000015
+	n00000001:port2 -> n00000007:port0 [style=dashed]
+	n00000001:port3 -> n00000019 [style=dashed]
+	n00000001:port3 -> n00000007:port0 [style=dashed]
+	n00000001:port4 -> n0000001d [style=dashed]
+	n00000001:port4 -> n00000007:port0 [style=dashed]
+	n00000007 [label="{{<port0> 0 | <port1> 1} | pisp-fe\n/dev/v4l-subdev1 | {<port2> 2 | <port3> 3 | <port4> 4}}", shape=Mrecord, style=filled, fillcolor=green]
+	n00000007:port2 -> n00000021
+	n00000007:port3 -> n00000025 [style=dashed]
+	n00000007:port4 -> n00000029
+	n0000000d [label="{imx219 6-0010\n/dev/v4l-subdev2 | {<port0> 0}}", shape=Mrecord, style=filled, fillcolor=green]
+	n0000000d:port0 -> n00000001:port0 [style=bold]
+	n00000011 [label="rp1-cfe-csi2-ch0\n/dev/video0", shape=box, style=filled, fillcolor=yellow]
+	n00000015 [label="rp1-cfe-csi2-ch1\n/dev/video1", shape=box, style=filled, fillcolor=yellow]
+	n00000019 [label="rp1-cfe-csi2-ch2\n/dev/video2", shape=box, style=filled, fillcolor=yellow]
+	n0000001d [label="rp1-cfe-csi2-ch3\n/dev/video3", shape=box, style=filled, fillcolor=yellow]
+	n00000021 [label="rp1-cfe-fe-image0\n/dev/video4", shape=box, style=filled, fillcolor=yellow]
+	n00000025 [label="rp1-cfe-fe-image1\n/dev/video5", shape=box, style=filled, fillcolor=yellow]
+	n00000029 [label="rp1-cfe-fe-stats\n/dev/video6", shape=box, style=filled, fillcolor=yellow]
+	n0000002d [label="rp1-cfe-fe-config\n/dev/video7", shape=box, style=filled, fillcolor=yellow]
+	n0000002d -> n00000007:port1
+}
diff --git a/Documentation/admin-guide/media/raspberrypi-rp1-cfe.rst b/Documentation/admin-guide/media/raspberrypi-rp1-cfe.rst
new file mode 100644
index 000000000000..668d978a9875
--- /dev/null
+++ b/Documentation/admin-guide/media/raspberrypi-rp1-cfe.rst
@@ -0,0 +1,78 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+============================================
+Raspberry Pi PiSP Camera Front End (rp1-cfe)
+============================================
+
+The PiSP Camera Front End
+=========================
+
+The PiSP Camera Front End (CFE) is a module which combines a CSI-2 receiver with
+a simple ISP, called the Front End (FE).
+
+The CFE has four DMA engines and can write frames from four separate streams
+received from the CSI-2 to the memory. One of those streams can also be routed
+directly to the FE, which can do minimal image processing, write two versions
+(e.g. non-scaled and downscaled versions) of the received frames to memory and
+provide statistics of the received frames.
+
+The FE registers are documented in the `Raspberry Pi Image Signal Processor
+(ISP) Specification document
+<https://datasheets.raspberrypi.com/camera/raspberry-pi-image-signal-processor-specification.pdf>`_,
+and example code for FE can be found in `libpisp
+<https://github.com/raspberrypi/libpisp>`_.
+
+The rp1-cfe driver
+==================
+
+The Raspberry Pi PiSP Camera Front End (rp1-cfe) driver is located under
+drivers/media/platform/raspberrypi/rp1-cfe. It uses the `V4L2 API` to register
+a number of video capture and output devices, the `V4L2 subdev API` to register
+subdevices for the CSI-2 received and the FE that connects the video devices in
+a single media graph realized using the `Media Controller (MC) API`.
+
+The media topology registered by the `rp1-cfe` driver, in this particular
+example connected to an imx219 sensor, is the following one:
+
+.. _rp1-cfe-topology:
+
+.. kernel-figure:: raspberrypi-rp1-cfe.dot
+    :alt:   Diagram of an example media pipeline topology
+    :align: center
+
+The media graph contains the following video device nodes:
+
+- rp1-cfe-csi2-ch0: capture device for the first CSI-2 stream
+- rp1-cfe-csi2-ch1: capture device for the second CSI-2 stream
+- rp1-cfe-csi2-ch2: capture device for the third CSI-2 stream
+- rp1-cfe-csi2-ch3: capture device for the fourth CSI-2 stream
+- rp1-cfe-fe-image0: capture device for the first FE output
+- rp1-cfe-fe-image1: capture device for the second FE output
+- rp1-cfe-fe-stats: capture device for the FE statistics
+- rp1-cfe-fe-config: output device for FE configuration
+
+rp1-cfe-csi2-chX
+----------------
+
+The rp1-cfe-csi2-chX capture devices are normal V4L2 capture devices which
+can be used to capture video frames or metadata received from the CSI-2.
+
+rp1-cfe-fe-image0, rp1-cfe-fe-image1
+------------------------------------
+
+The rp1-cfe-fe-image0 and rp1-cfe-fe-image1 capture devices are used to write
+the processed frames to memory.
+
+rp1-cfe-fe-stats
+----------------
+
+The format of the FE statistics buffer is defined by
+:c:type:`pisp_statistics` C structure and the meaning of each parameter is
+described in the `PiSP specification` document.
+
+rp1-cfe-fe-config
+-----------------
+
+The format of the FE configuration buffer is defined by
+:c:type:`pisp_fe_config` C structure and the meaning of each parameter is
+described in the `PiSP specification` document.
diff --git a/Documentation/admin-guide/media/v4l-drivers.rst b/Documentation/admin-guide/media/v4l-drivers.rst
index c15a6bb952d9..20be545e866c 100644
--- a/Documentation/admin-guide/media/v4l-drivers.rst
+++ b/Documentation/admin-guide/media/v4l-drivers.rst
@@ -25,6 +25,7 @@ Video4Linux (V4L) driver-specific documentation
 	raspberrypi-pisp-be
 	rcar-fdp1
 	rkisp1
+	raspberrypi-rp1-cfe
 	saa7134
 	si470x
 	si4713

-- 
2.34.1