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Add documentation for rp1-cfe driver. Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com> Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
79 lines
3.0 KiB
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79 lines
3.0 KiB
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.. SPDX-License-Identifier: GPL-2.0
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============================================
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Raspberry Pi PiSP Camera Front End (rp1-cfe)
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============================================
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The PiSP Camera Front End
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=========================
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The PiSP Camera Front End (CFE) is a module which combines a CSI-2 receiver with
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a simple ISP, called the Front End (FE).
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The CFE has four DMA engines and can write frames from four separate streams
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received from the CSI-2 to the memory. One of those streams can also be routed
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directly to the FE, which can do minimal image processing, write two versions
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(e.g. non-scaled and downscaled versions) of the received frames to memory and
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provide statistics of the received frames.
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The FE registers are documented in the `Raspberry Pi Image Signal Processor
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(ISP) Specification document
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<https://datasheets.raspberrypi.com/camera/raspberry-pi-image-signal-processor-specification.pdf>`_,
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and example code for FE can be found in `libpisp
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<https://github.com/raspberrypi/libpisp>`_.
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The rp1-cfe driver
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==================
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The Raspberry Pi PiSP Camera Front End (rp1-cfe) driver is located under
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drivers/media/platform/raspberrypi/rp1-cfe. It uses the `V4L2 API` to register
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a number of video capture and output devices, the `V4L2 subdev API` to register
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subdevices for the CSI-2 received and the FE that connects the video devices in
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a single media graph realized using the `Media Controller (MC) API`.
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The media topology registered by the `rp1-cfe` driver, in this particular
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example connected to an imx219 sensor, is the following one:
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.. _rp1-cfe-topology:
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.. kernel-figure:: raspberrypi-rp1-cfe.dot
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:alt: Diagram of an example media pipeline topology
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:align: center
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The media graph contains the following video device nodes:
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- rp1-cfe-csi2-ch0: capture device for the first CSI-2 stream
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- rp1-cfe-csi2-ch1: capture device for the second CSI-2 stream
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- rp1-cfe-csi2-ch2: capture device for the third CSI-2 stream
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- rp1-cfe-csi2-ch3: capture device for the fourth CSI-2 stream
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- rp1-cfe-fe-image0: capture device for the first FE output
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- rp1-cfe-fe-image1: capture device for the second FE output
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- rp1-cfe-fe-stats: capture device for the FE statistics
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- rp1-cfe-fe-config: output device for FE configuration
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rp1-cfe-csi2-chX
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----------------
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The rp1-cfe-csi2-chX capture devices are normal V4L2 capture devices which
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can be used to capture video frames or metadata received from the CSI-2.
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rp1-cfe-fe-image0, rp1-cfe-fe-image1
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------------------------------------
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The rp1-cfe-fe-image0 and rp1-cfe-fe-image1 capture devices are used to write
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the processed frames to memory.
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rp1-cfe-fe-stats
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----------------
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The format of the FE statistics buffer is defined by
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:c:type:`pisp_statistics` C structure and the meaning of each parameter is
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described in the `PiSP specification` document.
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rp1-cfe-fe-config
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-----------------
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The format of the FE configuration buffer is defined by
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:c:type:`pisp_fe_config` C structure and the meaning of each parameter is
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described in the `PiSP specification` document.
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