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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..0fcf46f26276 --- /dev/null +++ b/Documentation/admin-guide/media/raspberrypi-pisp-be.rst @@ -0,0 +1,109 @@ +.. 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 (PiSP) Specification document`_ + +The PiSP Back End ISP processes images in tiles. 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 <https://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`. + +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 + + +The media graph 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 +`Raspberry Pi Image Signal Processor (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 `Raspberry Pi Image Signal Processor (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. + +.. _Raspberry Pi Image Signal Processor (PiSP) Specification document: https://datasheets.raspberrypi.com/camera/raspberry-pi-image-signal-processor-specification.pdf |