167 lines
6.2 KiB
ReStructuredText
167 lines
6.2 KiB
ReStructuredText
Digital TV (DVB) devices
|
|
------------------------
|
|
|
|
Digital TV Common functions
|
|
---------------------------
|
|
|
|
.. kernel-doc:: drivers/media/dvb-core/dvb_math.h
|
|
|
|
.. kernel-doc:: drivers/media/dvb-core/dvbdev.h
|
|
|
|
|
|
|
|
.. kernel-doc:: drivers/media/dvb-core/dvb_math.h
|
|
:export: drivers/media/dvb-core/dvb_math.c
|
|
|
|
.. kernel-doc:: drivers/media/dvb-core/dvbdev.h
|
|
:export: drivers/media/dvb-core/dvbdev.c
|
|
|
|
Digital TV Ring buffer
|
|
----------------------
|
|
|
|
Those routines implement ring buffers used to handle digital TV data and
|
|
copy it from/to userspace.
|
|
|
|
.. note::
|
|
|
|
1) For performance reasons read and write routines don't check buffer sizes
|
|
and/or number of bytes free/available. This has to be done before these
|
|
routines are called. For example:
|
|
|
|
.. code-block:: c
|
|
|
|
/* write @buflen: bytes */
|
|
free = dvb_ringbuffer_free(rbuf);
|
|
if (free >= buflen)
|
|
count = dvb_ringbuffer_write(rbuf, buffer, buflen);
|
|
else
|
|
/* do something */
|
|
|
|
/* read min. 1000, max. @bufsize: bytes */
|
|
avail = dvb_ringbuffer_avail(rbuf);
|
|
if (avail >= 1000)
|
|
count = dvb_ringbuffer_read(rbuf, buffer, min(avail, bufsize));
|
|
else
|
|
/* do something */
|
|
|
|
2) If there is exactly one reader and one writer, there is no need
|
|
to lock read or write operations.
|
|
Two or more readers must be locked against each other.
|
|
Flushing the buffer counts as a read operation.
|
|
Resetting the buffer counts as a read and write operation.
|
|
Two or more writers must be locked against each other.
|
|
|
|
.. kernel-doc:: drivers/media/dvb-core/dvb_ringbuffer.h
|
|
|
|
|
|
Digital TV Frontend kABI
|
|
------------------------
|
|
|
|
Digital TV Frontend
|
|
~~~~~~~~~~~~~~~~~~~
|
|
|
|
The Digital TV Frontend kABI defines a driver-internal interface for
|
|
registering low-level, hardware specific driver to a hardware independent
|
|
frontend layer. It is only of interest for Digital TV device driver writers.
|
|
The header file for this API is named dvb_frontend.h and located in
|
|
drivers/media/dvb-core.
|
|
|
|
Before using the Digital TV frontend core, the bridge driver should attach
|
|
the frontend demod, tuner and SEC devices and call
|
|
:c:func:`dvb_register_frontend()`,
|
|
in order to register the new frontend at the subsystem. At device
|
|
detach/removal, the bridge driver should call
|
|
:c:func:`dvb_unregister_frontend()` to
|
|
remove the frontend from the core and then :c:func:`dvb_frontend_detach()`
|
|
to free the memory allocated by the frontend drivers.
|
|
|
|
The drivers should also call :c:func:`dvb_frontend_suspend()` as part of
|
|
their handler for the :c:type:`device_driver`.\ ``suspend()``, and
|
|
:c:func:`dvb_frontend_resume()` as
|
|
part of their handler for :c:type:`device_driver`.\ ``resume()``.
|
|
|
|
A few other optional functions are provided to handle some special cases.
|
|
|
|
.. kernel-doc:: drivers/media/dvb-core/dvb_frontend.h
|
|
|
|
|
|
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
|
|
drivers/media/dvb-core.
|
|
|
|
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
|
|
&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
|
|
------------------
|
|
|
|
Demux Callback
|
|
~~~~~~~~~~~~~~
|
|
|
|
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.
|
|
|
|
.. kernel-doc:: drivers/media/dvb-core/demux.h
|
|
|
|
Digital TV Conditional Access kABI
|
|
----------------------------------
|
|
|
|
.. kernel-doc:: drivers/media/dvb-core/dvb_ca_en50221.h
|