]>
Commit | Line | Data |
---|---|---|
684ffa2d MCC |
1 | Digital TV (DVB) devices |
2 | ------------------------ | |
3 | ||
4 | Digital TV Common functions | |
5 | --------------------------- | |
6 | ||
7 | .. kernel-doc:: drivers/media/dvb-core/dvb_math.h | |
8 | ||
9 | .. kernel-doc:: drivers/media/dvb-core/dvb_ringbuffer.h | |
10 | ||
11 | .. kernel-doc:: drivers/media/dvb-core/dvbdev.h | |
12 | ||
13 | ||
d2f01985 MCC |
14 | |
15 | .. kernel-doc:: drivers/media/dvb-core/dvb_math.h | |
16 | :export: drivers/media/dvb-core/dvb_math.c | |
17 | ||
18 | .. kernel-doc:: drivers/media/dvb-core/dvbdev.h | |
19 | :export: drivers/media/dvb-core/dvbdev.c | |
20 | ||
21 | ||
22 | ||
684ffa2d MCC |
23 | Digital TV Frontend kABI |
24 | ------------------------ | |
25 | ||
26 | Digital TV Frontend | |
27 | ~~~~~~~~~~~~~~~~~~~ | |
28 | ||
29 | The Digital TV Frontend kABI defines a driver-internal interface for | |
30 | registering low-level, hardware specific driver to a hardware independent | |
31 | frontend layer. It is only of interest for Digital TV device driver writers. | |
32 | The header file for this API is named dvb_frontend.h and located in | |
33 | drivers/media/dvb-core. | |
34 | ||
35 | Before using the Digital TV frontend core, the bridge driver should attach | |
d2f01985 MCC |
36 | the frontend demod, tuner and SEC devices and call |
37 | :cpp:func:`dvb_register_frontend()`, | |
684ffa2d | 38 | in order to register the new frontend at the subsystem. At device |
d2f01985 MCC |
39 | detach/removal, the bridge driver should call |
40 | :cpp:func:`dvb_unregister_frontend()` to | |
41 | remove the frontend from the core and then :cpp:func:`dvb_frontend_detach()` | |
42 | to free the memory allocated by the frontend drivers. | |
684ffa2d | 43 | |
d2f01985 MCC |
44 | The drivers should also call :cpp:func:`dvb_frontend_suspend()` as part of |
45 | their handler for the :c:type:`device_driver`.\ ``suspend()``, and | |
46 | :cpp:func:`dvb_frontend_resume()` as | |
47 | part of their handler for :c:type:`device_driver`.\ ``resume()``. | |
684ffa2d | 48 | |
d2f01985 | 49 | A few other optional functions are provided to handle some special cases. |
684ffa2d MCC |
50 | |
51 | .. kernel-doc:: drivers/media/dvb-core/dvb_frontend.h | |
52 | ||
53 | ||
54 | Digital TV Demux kABI | |
55 | --------------------- | |
56 | ||
57 | Digital TV Demux | |
58 | ~~~~~~~~~~~~~~~~ | |
59 | ||
60 | The Kernel Digital TV Demux kABI defines a driver-internal interface for | |
61 | registering low-level, hardware specific driver to a hardware independent | |
62 | demux layer. It is only of interest for Digital TV device driver writers. | |
63 | The header file for this kABI is named demux.h and located in | |
64 | drivers/media/dvb-core. | |
65 | ||
66 | The demux kABI should be implemented for each demux in the system. It is | |
67 | used to select the TS source of a demux and to manage the demux resources. | |
68 | When the demux client allocates a resource via the demux kABI, it receives | |
69 | a pointer to the kABI of that resource. | |
70 | ||
71 | Each demux receives its TS input from a DVB front-end or from memory, as | |
72 | set via this demux kABI. In a system with more than one front-end, the kABI | |
73 | can be used to select one of the DVB front-ends as a TS source for a demux, | |
74 | unless this is fixed in the HW platform. | |
75 | ||
76 | The demux kABI only controls front-ends regarding to their connections with | |
77 | demuxes; the kABI used to set the other front-end parameters, such as | |
78 | tuning, are devined via the Digital TV Frontend kABI. | |
79 | ||
80 | The functions that implement the abstract interface demux should be defined | |
81 | static or module private and registered to the Demux core for external | |
82 | access. It is not necessary to implement every function in the struct | |
83 | &dmx_demux. For example, a demux interface might support Section filtering, | |
84 | but not PES filtering. The kABI client is expected to check the value of any | |
d2f01985 | 85 | function pointer before calling the function: the value of ``NULL`` means |
684ffa2d MCC |
86 | that the function is not available. |
87 | ||
88 | Whenever the functions of the demux API modify shared data, the | |
89 | possibilities of lost update and race condition problems should be | |
90 | addressed, e.g. by protecting parts of code with mutexes. | |
91 | ||
92 | Note that functions called from a bottom half context must not sleep. | |
d2f01985 | 93 | Even a simple memory allocation without using ``GFP_ATOMIC`` can result in a |
684ffa2d MCC |
94 | kernel thread being put to sleep if swapping is needed. For example, the |
95 | Linux Kernel calls the functions of a network device interface from a | |
96 | bottom half context. Thus, if a demux kABI function is called from network | |
97 | device code, the function must not sleep. | |
98 | ||
99 | ||
100 | ||
101 | Demux Callback API | |
102 | ------------------ | |
103 | ||
104 | Demux Callback | |
105 | ~~~~~~~~~~~~~~ | |
106 | ||
107 | This kernel-space API comprises the callback functions that deliver filtered | |
108 | data to the demux client. Unlike the other DVB kABIs, these functions are | |
109 | provided by the client and called from the demux code. | |
110 | ||
111 | The function pointers of this abstract interface are not packed into a | |
112 | structure as in the other demux APIs, because the callback functions are | |
113 | registered and used independent of each other. As an example, it is possible | |
114 | for the API client to provide several callback functions for receiving TS | |
115 | packets and no callbacks for PES packets or sections. | |
116 | ||
117 | The functions that implement the callback API need not be re-entrant: when | |
118 | a demux driver calls one of these functions, the driver is not allowed to | |
119 | call the function again before the original call returns. If a callback is | |
120 | triggered by a hardware interrupt, it is recommended to use the Linux | |
121 | bottom half mechanism or start a tasklet instead of making the callback | |
122 | function call directly from a hardware interrupt. | |
123 | ||
d2f01985 | 124 | This mechanism is implemented by :cpp:func:`dmx_ts_cb()` and :cpp:func:`dmx_section_cb()` |
684ffa2d MCC |
125 | callbacks. |
126 | ||
684ffa2d MCC |
127 | .. kernel-doc:: drivers/media/dvb-core/demux.h |
128 | ||
684ffa2d MCC |
129 | Digital TV Conditional Access kABI |
130 | ---------------------------------- | |
131 | ||
132 | .. kernel-doc:: drivers/media/dvb-core/dvb_ca_en50221.h |