Mauro Carvalho Chehab | f2ac8ce8 | 2018-08-30 10:20:04 -0400 | [diff] [blame] | 1 | .. SPDX-License-Identifier: GPL-2.0 |
| 2 | |
Mauro Carvalho Chehab | 5b3b8c8 | 2017-09-19 16:54:15 -0400 | [diff] [blame] | 3 | Digital TV Demux kABI |
| 4 | --------------------- |
| 5 | |
| 6 | Digital TV Demux |
| 7 | ~~~~~~~~~~~~~~~~ |
| 8 | |
| 9 | The Kernel Digital TV Demux kABI defines a driver-internal interface for |
| 10 | registering low-level, hardware specific driver to a hardware independent |
| 11 | demux layer. It is only of interest for Digital TV device driver writers. |
Mauro Carvalho Chehab | 1607b8b | 2017-09-19 17:05:14 -0400 | [diff] [blame] | 12 | The header file for this kABI is named ``demux.h`` and located in |
Mauro Carvalho Chehab | fada193 | 2017-12-28 13:03:51 -0500 | [diff] [blame] | 13 | ``include/media``. |
Mauro Carvalho Chehab | 5b3b8c8 | 2017-09-19 16:54:15 -0400 | [diff] [blame] | 14 | |
| 15 | The demux kABI should be implemented for each demux in the system. It is |
| 16 | used to select the TS source of a demux and to manage the demux resources. |
| 17 | When the demux client allocates a resource via the demux kABI, it receives |
| 18 | a pointer to the kABI of that resource. |
| 19 | |
| 20 | Each demux receives its TS input from a DVB front-end or from memory, as |
| 21 | set via this demux kABI. In a system with more than one front-end, the kABI |
| 22 | can be used to select one of the DVB front-ends as a TS source for a demux, |
| 23 | unless this is fixed in the HW platform. |
| 24 | |
| 25 | The demux kABI only controls front-ends regarding to their connections with |
| 26 | demuxes; the kABI used to set the other front-end parameters, such as |
| 27 | tuning, are devined via the Digital TV Frontend kABI. |
| 28 | |
| 29 | The functions that implement the abstract interface demux should be defined |
| 30 | static or module private and registered to the Demux core for external |
| 31 | access. It is not necessary to implement every function in the struct |
Mauro Carvalho Chehab | 1607b8b | 2017-09-19 17:05:14 -0400 | [diff] [blame] | 32 | :c:type:`dmx_demux`. For example, a demux interface might support Section filtering, |
Mauro Carvalho Chehab | 5b3b8c8 | 2017-09-19 16:54:15 -0400 | [diff] [blame] | 33 | but not PES filtering. The kABI client is expected to check the value of any |
| 34 | function pointer before calling the function: the value of ``NULL`` means |
| 35 | that the function is not available. |
| 36 | |
| 37 | Whenever the functions of the demux API modify shared data, the |
| 38 | possibilities of lost update and race condition problems should be |
| 39 | addressed, e.g. by protecting parts of code with mutexes. |
| 40 | |
| 41 | Note that functions called from a bottom half context must not sleep. |
| 42 | Even a simple memory allocation without using ``GFP_ATOMIC`` can result in a |
| 43 | kernel thread being put to sleep if swapping is needed. For example, the |
| 44 | Linux Kernel calls the functions of a network device interface from a |
| 45 | bottom half context. Thus, if a demux kABI function is called from network |
| 46 | device code, the function must not sleep. |
| 47 | |
Mauro Carvalho Chehab | 5b3b8c8 | 2017-09-19 16:54:15 -0400 | [diff] [blame] | 48 | Demux Callback API |
| 49 | ~~~~~~~~~~~~~~~~~~ |
| 50 | |
| 51 | This kernel-space API comprises the callback functions that deliver filtered |
| 52 | data to the demux client. Unlike the other DVB kABIs, these functions are |
| 53 | provided by the client and called from the demux code. |
| 54 | |
| 55 | The function pointers of this abstract interface are not packed into a |
| 56 | structure as in the other demux APIs, because the callback functions are |
| 57 | registered and used independent of each other. As an example, it is possible |
| 58 | for the API client to provide several callback functions for receiving TS |
| 59 | packets and no callbacks for PES packets or sections. |
| 60 | |
| 61 | The functions that implement the callback API need not be re-entrant: when |
| 62 | a demux driver calls one of these functions, the driver is not allowed to |
| 63 | call the function again before the original call returns. If a callback is |
| 64 | triggered by a hardware interrupt, it is recommended to use the Linux |
| 65 | bottom half mechanism or start a tasklet instead of making the callback |
| 66 | function call directly from a hardware interrupt. |
| 67 | |
| 68 | This mechanism is implemented by :c:func:`dmx_ts_cb()` and :c:func:`dmx_section_cb()` |
| 69 | callbacks. |
| 70 | |
Mauro Carvalho Chehab | 8c6b186 | 2017-09-19 19:03:14 -0400 | [diff] [blame] | 71 | Digital TV Demux device registration functions and data structures |
| 72 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| 73 | |
Mauro Carvalho Chehab | fada193 | 2017-12-28 13:03:51 -0500 | [diff] [blame] | 74 | .. kernel-doc:: include/media/dmxdev.h |
Mauro Carvalho Chehab | 8c6b186 | 2017-09-19 19:03:14 -0400 | [diff] [blame] | 75 | |
| 76 | High-level Digital TV demux interface |
| 77 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| 78 | |
Mauro Carvalho Chehab | fada193 | 2017-12-28 13:03:51 -0500 | [diff] [blame] | 79 | .. kernel-doc:: include/media/dvb_demux.h |
Mauro Carvalho Chehab | 8c6b186 | 2017-09-19 19:03:14 -0400 | [diff] [blame] | 80 | |
| 81 | Driver-internal low-level hardware specific driver demux interface |
| 82 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
Mauro Carvalho Chehab | 1607b8b | 2017-09-19 17:05:14 -0400 | [diff] [blame] | 83 | |
Mauro Carvalho Chehab | fada193 | 2017-12-28 13:03:51 -0500 | [diff] [blame] | 84 | .. kernel-doc:: include/media/demux.h |