Mauro Carvalho Chehab | 684ffa2 | 2016-07-17 08:22:23 -0300 | [diff] [blame] | 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 | |
Mauro Carvalho Chehab | 684ffa2 | 2016-07-17 08:22:23 -0300 | [diff] [blame] | 9 | .. kernel-doc:: drivers/media/dvb-core/dvbdev.h |
| 10 | |
| 11 | |
Mauro Carvalho Chehab | d2f0198 | 2016-07-17 11:25:37 -0300 | [diff] [blame] | 12 | |
| 13 | .. kernel-doc:: drivers/media/dvb-core/dvb_math.h |
| 14 | :export: drivers/media/dvb-core/dvb_math.c |
| 15 | |
| 16 | .. kernel-doc:: drivers/media/dvb-core/dvbdev.h |
| 17 | :export: drivers/media/dvb-core/dvbdev.c |
| 18 | |
Mauro Carvalho Chehab | b6df512 | 2016-08-29 08:39:32 -0300 | [diff] [blame] | 19 | Digital TV Ring buffer |
| 20 | ---------------------- |
| 21 | |
| 22 | Those routines implement ring buffers used to handle digital TV data and |
| 23 | copy it from/to userspace. |
| 24 | |
| 25 | .. note:: |
| 26 | |
| 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: |
| 30 | |
| 31 | .. code-block:: c |
| 32 | |
| 33 | /* write @buflen: bytes */ |
| 34 | free = dvb_ringbuffer_free(rbuf); |
| 35 | if (free >= buflen) |
| 36 | count = dvb_ringbuffer_write(rbuf, buffer, buflen); |
| 37 | else |
| 38 | /* do something */ |
| 39 | |
| 40 | /* read min. 1000, max. @bufsize: bytes */ |
| 41 | avail = dvb_ringbuffer_avail(rbuf); |
| 42 | if (avail >= 1000) |
| 43 | count = dvb_ringbuffer_read(rbuf, buffer, min(avail, bufsize)); |
| 44 | else |
| 45 | /* do something */ |
| 46 | |
| 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. |
| 53 | |
| 54 | .. kernel-doc:: drivers/media/dvb-core/dvb_ringbuffer.h |
Mauro Carvalho Chehab | d2f0198 | 2016-07-17 11:25:37 -0300 | [diff] [blame] | 55 | |
| 56 | |
Mauro Carvalho Chehab | 684ffa2 | 2016-07-17 08:22:23 -0300 | [diff] [blame] | 57 | Digital TV Frontend kABI |
| 58 | ------------------------ |
| 59 | |
| 60 | Digital TV Frontend |
| 61 | ~~~~~~~~~~~~~~~~~~~ |
| 62 | |
| 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. |
| 68 | |
| 69 | Before using the Digital TV frontend core, the bridge driver should attach |
Mauro Carvalho Chehab | d2f0198 | 2016-07-17 11:25:37 -0300 | [diff] [blame] | 70 | the frontend demod, tuner and SEC devices and call |
Mauro Carvalho Chehab | 7b998ba | 2016-07-23 07:21:06 -0300 | [diff] [blame] | 71 | :c:func:`dvb_register_frontend()`, |
Mauro Carvalho Chehab | 684ffa2 | 2016-07-17 08:22:23 -0300 | [diff] [blame] | 72 | in order to register the new frontend at the subsystem. At device |
Mauro Carvalho Chehab | d2f0198 | 2016-07-17 11:25:37 -0300 | [diff] [blame] | 73 | detach/removal, the bridge driver should call |
Mauro Carvalho Chehab | 7b998ba | 2016-07-23 07:21:06 -0300 | [diff] [blame] | 74 | :c:func:`dvb_unregister_frontend()` to |
| 75 | remove the frontend from the core and then :c:func:`dvb_frontend_detach()` |
Mauro Carvalho Chehab | d2f0198 | 2016-07-17 11:25:37 -0300 | [diff] [blame] | 76 | to free the memory allocated by the frontend drivers. |
Mauro Carvalho Chehab | 684ffa2 | 2016-07-17 08:22:23 -0300 | [diff] [blame] | 77 | |
Mauro Carvalho Chehab | 7b998ba | 2016-07-23 07:21:06 -0300 | [diff] [blame] | 78 | The drivers should also call :c:func:`dvb_frontend_suspend()` as part of |
Mauro Carvalho Chehab | d2f0198 | 2016-07-17 11:25:37 -0300 | [diff] [blame] | 79 | their handler for the :c:type:`device_driver`.\ ``suspend()``, and |
Mauro Carvalho Chehab | 7b998ba | 2016-07-23 07:21:06 -0300 | [diff] [blame] | 80 | :c:func:`dvb_frontend_resume()` as |
Mauro Carvalho Chehab | d2f0198 | 2016-07-17 11:25:37 -0300 | [diff] [blame] | 81 | part of their handler for :c:type:`device_driver`.\ ``resume()``. |
Mauro Carvalho Chehab | 684ffa2 | 2016-07-17 08:22:23 -0300 | [diff] [blame] | 82 | |
Mauro Carvalho Chehab | d2f0198 | 2016-07-17 11:25:37 -0300 | [diff] [blame] | 83 | A few other optional functions are provided to handle some special cases. |
Mauro Carvalho Chehab | 684ffa2 | 2016-07-17 08:22:23 -0300 | [diff] [blame] | 84 | |
| 85 | .. kernel-doc:: drivers/media/dvb-core/dvb_frontend.h |
| 86 | |
| 87 | |
| 88 | Digital TV Demux kABI |
| 89 | --------------------- |
| 90 | |
| 91 | Digital TV Demux |
| 92 | ~~~~~~~~~~~~~~~~ |
| 93 | |
| 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. |
| 99 | |
| 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. |
| 104 | |
| 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. |
| 109 | |
| 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. |
| 113 | |
| 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 |
Mauro Carvalho Chehab | d2f0198 | 2016-07-17 11:25:37 -0300 | [diff] [blame] | 119 | function pointer before calling the function: the value of ``NULL`` means |
Mauro Carvalho Chehab | 684ffa2 | 2016-07-17 08:22:23 -0300 | [diff] [blame] | 120 | that the function is not available. |
| 121 | |
| 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. |
| 125 | |
| 126 | Note that functions called from a bottom half context must not sleep. |
Mauro Carvalho Chehab | d2f0198 | 2016-07-17 11:25:37 -0300 | [diff] [blame] | 127 | Even a simple memory allocation without using ``GFP_ATOMIC`` can result in a |
Mauro Carvalho Chehab | 684ffa2 | 2016-07-17 08:22:23 -0300 | [diff] [blame] | 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. |
| 132 | |
| 133 | |
| 134 | |
| 135 | Demux Callback API |
| 136 | ------------------ |
| 137 | |
| 138 | Demux Callback |
| 139 | ~~~~~~~~~~~~~~ |
| 140 | |
| 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. |
| 144 | |
| 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. |
| 150 | |
| 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. |
| 157 | |
Mauro Carvalho Chehab | 1b81f01 | 2016-08-19 12:00:43 -0300 | [diff] [blame] | 158 | This mechanism is implemented by :c:func:`dmx_ts_cb()` and :c:func:`dmx_section_cb()` |
Mauro Carvalho Chehab | 684ffa2 | 2016-07-17 08:22:23 -0300 | [diff] [blame] | 159 | callbacks. |
| 160 | |
Mauro Carvalho Chehab | 684ffa2 | 2016-07-17 08:22:23 -0300 | [diff] [blame] | 161 | .. kernel-doc:: drivers/media/dvb-core/demux.h |
| 162 | |
Mauro Carvalho Chehab | 684ffa2 | 2016-07-17 08:22:23 -0300 | [diff] [blame] | 163 | Digital TV Conditional Access kABI |
| 164 | ---------------------------------- |
| 165 | |
| 166 | .. kernel-doc:: drivers/media/dvb-core/dvb_ca_en50221.h |