forked from Minki/linux
68 lines
2.5 KiB
Plaintext
68 lines
2.5 KiB
Plaintext
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Linux kernel media framework
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============================
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This document describes the Linux kernel media framework, its data structures,
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functions and their usage.
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Introduction
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------------
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The media controller API is documented in DocBook format in
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Documentation/DocBook/v4l/media-controller.xml. This document will focus on
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the kernel-side implementation of the media framework.
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Media device
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------------
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A media device is represented by a struct media_device instance, defined in
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include/media/media-device.h. Allocation of the structure is handled by the
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media device driver, usually by embedding the media_device instance in a
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larger driver-specific structure.
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Drivers register media device instances by calling
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media_device_register(struct media_device *mdev);
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The caller is responsible for initializing the media_device structure before
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registration. The following fields must be set:
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- dev must point to the parent device (usually a pci_dev, usb_interface or
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platform_device instance).
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- model must be filled with the device model name as a NUL-terminated UTF-8
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string. The device/model revision must not be stored in this field.
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The following fields are optional:
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- serial is a unique serial number stored as a NUL-terminated ASCII string.
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The field is big enough to store a GUID in text form. If the hardware
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doesn't provide a unique serial number this field must be left empty.
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- bus_info represents the location of the device in the system as a
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NUL-terminated ASCII string. For PCI/PCIe devices bus_info must be set to
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"PCI:" (or "PCIe:") followed by the value of pci_name(). For USB devices,
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the usb_make_path() function must be used. This field is used by
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applications to distinguish between otherwise identical devices that don't
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provide a serial number.
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- hw_revision is the hardware device revision in a driver-specific format.
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When possible the revision should be formatted with the KERNEL_VERSION
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macro.
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- driver_version is formatted with the KERNEL_VERSION macro. The version
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minor must be incremented when new features are added to the userspace API
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without breaking binary compatibility. The version major must be
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incremented when binary compatibility is broken.
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Upon successful registration a character device named media[0-9]+ is created.
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The device major and minor numbers are dynamic. The model name is exported as
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a sysfs attribute.
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Drivers unregister media device instances by calling
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media_device_unregister(struct media_device *mdev);
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Unregistering a media device that hasn't been registered is *NOT* safe.
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