Add documentation for the PiSP Back End memory-to-memory ISP.
Signed-off-by: Jacopo Mondi <jacopo.mondi@xxxxxxxxxxxxxxxx>
---
.../admin-guide/media/raspberrypi-pisp-be.dot | 20 ++++
.../admin-guide/media/raspberrypi-pisp-be.rst | 112 ++++++++++++++++++
.../admin-guide/media/v4l-drivers.rst | 1 +
3 files changed, 133 insertions(+)
create mode 100644 Documentation/admin-guide/media/raspberrypi-pisp-be.dot
create mode 100644 Documentation/admin-guide/media/raspberrypi-pisp-be.rst
diff --git a/Documentation/admin-guide/media/raspberrypi-pisp-be.dot b/Documentation/admin-guide/media/raspberrypi-pisp-be.dot
new file mode 100644
index 000000000000..55671dc1d443
--- /dev/null
+++ b/Documentation/admin-guide/media/raspberrypi-pisp-be.dot
@@ -0,0 +1,20 @@
+digraph board {
+ rankdir=TB
+ n00000001 [label="{{<port0> 0 | <port1> 1 | <port2> 2 | <port7> 7} | pispbe\n | {<port3> 3 | <port4> 4 | <port5> 5 | <port6> 6}}", shape=Mrecord, style=filled, fillcolor=green]
+ n00000001:port3 -> n0000001c [style=bold]
+ n00000001:port4 -> n00000022 [style=bold]
+ n00000001:port5 -> n00000028 [style=bold]
+ n00000001:port6 -> n0000002e [style=bold]
+ n0000000a [label="pispbe-input\n/dev/video0", shape=box, style=filled, fillcolor=yellow]
+ n0000000a -> n00000001:port0 [style=bold]
+ n00000010 [label="pispbe-tdn_input\n/dev/video1", shape=box, style=filled, fillcolor=yellow]
+ n00000010 -> n00000001:port1 [style=bold]
+ n00000016 [label="pispbe-stitch_input\n/dev/video2", shape=box, style=filled, fillcolor=yellow]
+ n00000016 -> n00000001:port2 [style=bold]
+ n0000001c [label="pispbe-output0\n/dev/video3", shape=box, style=filled, fillcolor=yellow]
+ n00000022 [label="pispbe-output1\n/dev/video4", shape=box, style=filled, fillcolor=yellow]
+ n00000028 [label="pispbe-tdn_output\n/dev/video5", shape=box, style=filled, fillcolor=yellow]
+ n0000002e [label="pispbe-stitch_output\n/dev/video6", shape=box, style=filled, fillcolor=yellow]
+ n00000034 [label="pispbe-config\n/dev/video7", shape=box, style=filled, fillcolor=yellow]
+ n00000034 -> n00000001:port7 [style=bold]
+}
diff --git a/Documentation/admin-guide/media/raspberrypi-pisp-be.rst b/Documentation/admin-guide/media/raspberrypi-pisp-be.rst
new file mode 100644
index 000000000000..60fb4a882d31
--- /dev/null
+++ b/Documentation/admin-guide/media/raspberrypi-pisp-be.rst
@@ -0,0 +1,112 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=========================================================
+Raspberry Pi PiSP Back End Memory-to-Memory ISP (pisp-be)
+=========================================================
+
+The PiSP Back End
+=================
+
+The PiSP Back End is a memory-to-memory Image Signal Processor (ISP) which reads
+image data from DRAM memory and performs image processing as specified by the
+application through the parameters in a configuration buffer, before writing
+pixel data back to memory through two distinct output channels.
+
+The ISP registers and programming model are documented in the `Raspberry Pi
+Image Signal Processor (ISP) Specification document
+<https://datasheets.raspberrypi.com/camera/raspberry-pi-image-signal-processor-specification.pdf>`_
+
+The PiSP Back End ISP processes images in tiles to allow concurrent processing
+of different images. The handling of image tessellation and the computation of
+low-level configuration parameters is realized by a free software library
+called `libpisp <https://github.com/raspberrypi/libpisp>`_.
+
+The full image processing pipeline, which involves capturing RAW Bayer data from
+an image sensor through a MIPI CSI-2 compatible capture interface, storing them
+in DRAM memory and processing them in the PiSP Back End to obtain images usable
+by an application is implemented in `libcamera <www.libcamera.org>`_ as part of
+the Raspberry Pi platform support.
+
+The pisp-be driver
+==================
+
+The Raspberry Pi PiSP Back End (pisp-be) driver is located under
+drivers/media/platform/raspberrypi/pisp-be. It uses the `V4L2 API` to register
+a number of video capture and output devices, the `V4L2 subdev API` to register
+a subdevice for the ISP that connects the video devices in a single media graph
+realized using the `Media Controller (MC) API`.
+
+As the PiSP Back End device processes images in tiles, it can be multiplexed
+between several different execution contexts. The driver registers two
+`contexts` represented as two distinct media graph instances but could
+potentially register more of them.
+
+The media topology registered by the `pisp-be` driver is represented below:
+
+.. _pips-be-topology:
+
+.. kernel-figure:: raspberrypi-pisp-be.dot
+ :alt: Diagram of the default media pipeline topology
+ :align: center
+
+
+Each media graph instance registers the following video device nodes:
+
+- pispbe-input: output device for images to be submitted to the ISP for
+ processing.
+- pispbe-tdn_input: output device for temporal denoise.
+- pispbe-stitch_input: output device for image stitching (HDR).
+- pispbe-output0: first capture device for processed images.
+- pispbe-output1: second capture device for processed images.
+- pispbe-tdn_output: capture device for temporal denoise.
+- pispbe-stitch_output: capture device for image stitching (HDR).
+- pispbe-config: output device for ISP configuration parameters.
+
+pispbe-input
+------------
+
+Images to be processed by the ISP are queued to the `pispbe-input` output device
+node. For a list of image formats supported as input to the ISP refer to the
+PiSP specification document.
+
+pispbe-tdn_input, pispbe-tdn_output
+-----------------------------------
+
+The `pispbe-tdn_input` output video device receives images to be processed by
+the temporal denoise block which are captured from the `pispbe-tdn_output`
+capture video device. Userspace is responsible for maintaining queues on both
+devices, and ensuring that buffers completed on the output are queued to the
+input.
+
+pispbe-stitch_input, pispbe-stitch_output
+-----------------------------------------
+
+To realize HDR (high dynamic range) image processing the image stitching and
+tonemapping blocks are used. The `pispbe-stitch_output` writes images to memory
+and the `pispbe-stitch_input` receives the previously written frame to process
+it along with the current input image. Userspace is responsible for maintaining
+queues on both devices, and ensuring that buffers completed on the output are
+queued to the input.
+
+pispbe-output0, pispbe-output1
+------------------------------
+
+The two capture devices write to memory the pixel data as processed by the ISP.
+
+pispbe-config
+-------------
+
+The `pispbe-config` output video devices receives a buffer of configuration
+parameters that define the desired image processing to be performed by the ISP.
+
+The format of the ISP configuration parameter is defined by
+:c:type:`pisp_be_tiles_config` C structure and the meaning of each parameter is
+described in the `PiSP specification` document.
+
+ISP configuration
+=================
+
+The ISP configuration is described solely by the content of the parameters
+buffer. The only parameter that userspace needs to configure using the V4L2 API
+is the image format on the output and capture video devices for validation of
+the content of the parameters buffer.
diff --git a/Documentation/admin-guide/media/v4l-drivers.rst b/Documentation/admin-guide/media/v4l-drivers.rst
index f4bb2605f07e..c15a6bb952d9 100644
--- a/Documentation/admin-guide/media/v4l-drivers.rst
+++ b/Documentation/admin-guide/media/v4l-drivers.rst
@@ -22,6 +22,7 @@ Video4Linux (V4L) driver-specific documentation
omap4_camera
philips
qcom_camss
+ raspberrypi-pisp-be
rcar-fdp1
rkisp1
saa7134
--
2.44.0
