1 Digital TV (DVB) devices
2 ------------------------
4 Digital TV Common functions
5 ---------------------------
7 .. kernel-doc:: drivers/media/dvb-core/dvb_math.h
9 .. kernel-doc:: drivers/media/dvb-core/dvbdev.h
13 .. kernel-doc:: drivers/media/dvb-core/dvb_math.h
14 :export: drivers/media/dvb-core/dvb_math.c
16 .. kernel-doc:: drivers/media/dvb-core/dvbdev.h
17 :export: drivers/media/dvb-core/dvbdev.c
19 Digital TV Ring buffer
20 ----------------------
22 Those routines implement ring buffers used to handle digital TV data and
23 copy it from/to userspace.
27 1) For performance reasons read and write routines don't check buffer sizes
28 and/or number of bytes free/available. This has to be done before these
29 routines are called. For example:
33 /* write @buflen: bytes */
34 free = dvb_ringbuffer_free(rbuf);
36 count = dvb_ringbuffer_write(rbuf, buffer, buflen);
40 /* read min. 1000, max. @bufsize: bytes */
41 avail = dvb_ringbuffer_avail(rbuf);
43 count = dvb_ringbuffer_read(rbuf, buffer, min(avail, bufsize));
47 2) If there is exactly one reader and one writer, there is no need
48 to lock read or write operations.
49 Two or more readers must be locked against each other.
50 Flushing the buffer counts as a read operation.
51 Resetting the buffer counts as a read and write operation.
52 Two or more writers must be locked against each other.
54 .. kernel-doc:: drivers/media/dvb-core/dvb_ringbuffer.h
57 Digital TV Frontend kABI
58 ------------------------
63 The Digital TV Frontend kABI defines a driver-internal interface for
64 registering low-level, hardware specific driver to a hardware independent
65 frontend layer. It is only of interest for Digital TV device driver writers.
66 The header file for this API is named dvb_frontend.h and located in
67 drivers/media/dvb-core.
69 Before using the Digital TV frontend core, the bridge driver should attach
70 the frontend demod, tuner and SEC devices and call
71 :c:func:`dvb_register_frontend()`,
72 in order to register the new frontend at the subsystem. At device
73 detach/removal, the bridge driver should call
74 :c:func:`dvb_unregister_frontend()` to
75 remove the frontend from the core and then :c:func:`dvb_frontend_detach()`
76 to free the memory allocated by the frontend drivers.
78 The drivers should also call :c:func:`dvb_frontend_suspend()` as part of
79 their handler for the :c:type:`device_driver`.\ ``suspend()``, and
80 :c:func:`dvb_frontend_resume()` as
81 part of their handler for :c:type:`device_driver`.\ ``resume()``.
83 A few other optional functions are provided to handle some special cases.
85 .. kernel-doc:: drivers/media/dvb-core/dvb_frontend.h
94 The Kernel Digital TV Demux kABI defines a driver-internal interface for
95 registering low-level, hardware specific driver to a hardware independent
96 demux layer. It is only of interest for Digital TV device driver writers.
97 The header file for this kABI is named demux.h and located in
98 drivers/media/dvb-core.
100 The demux kABI should be implemented for each demux in the system. It is
101 used to select the TS source of a demux and to manage the demux resources.
102 When the demux client allocates a resource via the demux kABI, it receives
103 a pointer to the kABI of that resource.
105 Each demux receives its TS input from a DVB front-end or from memory, as
106 set via this demux kABI. In a system with more than one front-end, the kABI
107 can be used to select one of the DVB front-ends as a TS source for a demux,
108 unless this is fixed in the HW platform.
110 The demux kABI only controls front-ends regarding to their connections with
111 demuxes; the kABI used to set the other front-end parameters, such as
112 tuning, are devined via the Digital TV Frontend kABI.
114 The functions that implement the abstract interface demux should be defined
115 static or module private and registered to the Demux core for external
116 access. It is not necessary to implement every function in the struct
117 &dmx_demux. For example, a demux interface might support Section filtering,
118 but not PES filtering. The kABI client is expected to check the value of any
119 function pointer before calling the function: the value of ``NULL`` means
120 that the function is not available.
122 Whenever the functions of the demux API modify shared data, the
123 possibilities of lost update and race condition problems should be
124 addressed, e.g. by protecting parts of code with mutexes.
126 Note that functions called from a bottom half context must not sleep.
127 Even a simple memory allocation without using ``GFP_ATOMIC`` can result in a
128 kernel thread being put to sleep if swapping is needed. For example, the
129 Linux Kernel calls the functions of a network device interface from a
130 bottom half context. Thus, if a demux kABI function is called from network
131 device code, the function must not sleep.
141 This kernel-space API comprises the callback functions that deliver filtered
142 data to the demux client. Unlike the other DVB kABIs, these functions are
143 provided by the client and called from the demux code.
145 The function pointers of this abstract interface are not packed into a
146 structure as in the other demux APIs, because the callback functions are
147 registered and used independent of each other. As an example, it is possible
148 for the API client to provide several callback functions for receiving TS
149 packets and no callbacks for PES packets or sections.
151 The functions that implement the callback API need not be re-entrant: when
152 a demux driver calls one of these functions, the driver is not allowed to
153 call the function again before the original call returns. If a callback is
154 triggered by a hardware interrupt, it is recommended to use the Linux
155 bottom half mechanism or start a tasklet instead of making the callback
156 function call directly from a hardware interrupt.
158 This mechanism is implemented by :c:func:`dmx_ts_cb()` and :c:func:`dmx_section_cb()`
161 .. kernel-doc:: drivers/media/dvb-core/demux.h
163 Digital TV Conditional Access kABI
164 ----------------------------------
166 .. kernel-doc:: drivers/media/dvb-core/dvb_ca_en50221.h