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diff --git a/Documentation/media/kapi/v4l2-intro.rst b/Documentation/media/kapi/v4l2-intro.rst deleted file mode 100644 index 4d54fa9d7a12..000000000000 --- a/Documentation/media/kapi/v4l2-intro.rst +++ /dev/null @@ -1,76 +0,0 @@ -.. SPDX-License-Identifier: GPL-2.0 - -Introduction ------------- - -The V4L2 drivers tend to be very complex due to the complexity of the -hardware: most devices have multiple ICs, export multiple device nodes in -/dev, and create also non-V4L2 devices such as DVB, ALSA, FB, I2C and input -(IR) devices. - -Especially the fact that V4L2 drivers have to setup supporting ICs to -do audio/video muxing/encoding/decoding makes it more complex than most. -Usually these ICs are connected to the main bridge driver through one or -more I2C buses, but other buses can also be used. Such devices are -called 'sub-devices'. - -For a long time the framework was limited to the video_device struct for -creating V4L device nodes and video_buf for handling the video buffers -(note that this document does not discuss the video_buf framework). - -This meant that all drivers had to do the setup of device instances and -connecting to sub-devices themselves. Some of this is quite complicated -to do right and many drivers never did do it correctly. - -There is also a lot of common code that could never be refactored due to -the lack of a framework. - -So this framework sets up the basic building blocks that all drivers -need and this same framework should make it much easier to refactor -common code into utility functions shared by all drivers. - -A good example to look at as a reference is the v4l2-pci-skeleton.c -source that is available in samples/v4l/. It is a skeleton driver for -a PCI capture card, and demonstrates how to use the V4L2 driver -framework. It can be used as a template for real PCI video capture driver. - -Structure of a V4L driver -------------------------- - -All drivers have the following structure: - -1) A struct for each device instance containing the device state. - -2) A way of initializing and commanding sub-devices (if any). - -3) Creating V4L2 device nodes (/dev/videoX, /dev/vbiX and /dev/radioX) - and keeping track of device-node specific data. - -4) Filehandle-specific structs containing per-filehandle data; - -5) video buffer handling. - -This is a rough schematic of how it all relates: - -.. code-block:: none - - device instances - | - +-sub-device instances - | - \-V4L2 device nodes - | - \-filehandle instances - - -Structure of the V4L2 framework -------------------------------- - -The framework closely resembles the driver structure: it has a v4l2_device -struct for the device instance data, a v4l2_subdev struct to refer to -sub-device instances, the video_device struct stores V4L2 device node data -and the v4l2_fh struct keeps track of filehandle instances. - -The V4L2 framework also optionally integrates with the media framework. If a -driver sets the struct v4l2_device mdev field, sub-devices and video nodes -will automatically appear in the media framework as entities. |