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- .. SPDX-License-Identifier: GPL-2.0
- Digital TV Demux kABI
- ---------------------
- Digital TV Demux
- ~~~~~~~~~~~~~~~~
- The Kernel Digital TV Demux kABI defines a driver-internal interface for
- registering low-level, hardware specific driver to a hardware independent
- demux layer. It is only of interest for Digital TV device driver writers.
- The header file for this kABI is named ``demux.h`` and located in
- ``include/media``.
- The demux kABI should be implemented for each demux in the system. It is
- used to select the TS source of a demux and to manage the demux resources.
- When the demux client allocates a resource via the demux kABI, it receives
- a pointer to the kABI of that resource.
- Each demux receives its TS input from a DVB front-end or from memory, as
- set via this demux kABI. In a system with more than one front-end, the kABI
- can be used to select one of the DVB front-ends as a TS source for a demux,
- unless this is fixed in the HW platform.
- The demux kABI only controls front-ends regarding to their connections with
- demuxes; the kABI used to set the other front-end parameters, such as
- tuning, are devined via the Digital TV Frontend kABI.
- The functions that implement the abstract interface demux should be defined
- static or module private and registered to the Demux core for external
- access. It is not necessary to implement every function in the struct
- :c:type:`dmx_demux`. For example, a demux interface might support Section filtering,
- but not PES filtering. The kABI client is expected to check the value of any
- function pointer before calling the function: the value of ``NULL`` means
- that the function is not available.
- Whenever the functions of the demux API modify shared data, the
- possibilities of lost update and race condition problems should be
- addressed, e.g. by protecting parts of code with mutexes.
- Note that functions called from a bottom half context must not sleep.
- Even a simple memory allocation without using ``GFP_ATOMIC`` can result in a
- kernel thread being put to sleep if swapping is needed. For example, the
- Linux Kernel calls the functions of a network device interface from a
- bottom half context. Thus, if a demux kABI function is called from network
- device code, the function must not sleep.
- Demux Callback API
- ~~~~~~~~~~~~~~~~~~
- This kernel-space API comprises the callback functions that deliver filtered
- data to the demux client. Unlike the other DVB kABIs, these functions are
- provided by the client and called from the demux code.
- The function pointers of this abstract interface are not packed into a
- structure as in the other demux APIs, because the callback functions are
- registered and used independent of each other. As an example, it is possible
- for the API client to provide several callback functions for receiving TS
- packets and no callbacks for PES packets or sections.
- The functions that implement the callback API need not be re-entrant: when
- a demux driver calls one of these functions, the driver is not allowed to
- call the function again before the original call returns. If a callback is
- triggered by a hardware interrupt, it is recommended to use the Linux
- bottom half mechanism or start a tasklet instead of making the callback
- function call directly from a hardware interrupt.
- This mechanism is implemented by :c:func:`dmx_ts_cb()` and :c:func:`dmx_section_cb()`
- callbacks.
- Digital TV Demux device registration functions and data structures
- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- .. kernel-doc:: include/media/dmxdev.h
- High-level Digital TV demux interface
- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- .. kernel-doc:: include/media/dvb_demux.h
- Driver-internal low-level hardware specific driver demux interface
- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- .. kernel-doc:: include/media/demux.h
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