From 5b3b8c81b47aa3ca473d310b1aa3ab93f0ec9c6b Mon Sep 17 00:00:00 2001 From: Mauro Carvalho Chehab Date: Tue, 19 Sep 2017 16:54:15 -0400 Subject: [PATCH] media: dtv-core.rst: split into multiple files Instead of document all kAPI into a single file, split it on multiple ones. That makes easier to maintain each part. As a side effect, it will produce multiple html pages, with is a good idea. No changes at the text. Just some chapter levels changed. Signed-off-by: Mauro Carvalho Chehab --- Documentation/media/kapi/dtv-ca.rst | 4 + Documentation/media/kapi/dtv-common.rst | 55 ++ Documentation/media/kapi/dtv-core.rst | 585 +--------------------- Documentation/media/kapi/dtv-demux.rst | 71 +++ Documentation/media/kapi/dtv-frontend.rst | 443 ++++++++++++++++ 5 files changed, 579 insertions(+), 579 deletions(-) create mode 100644 Documentation/media/kapi/dtv-ca.rst create mode 100644 Documentation/media/kapi/dtv-common.rst create mode 100644 Documentation/media/kapi/dtv-demux.rst create mode 100644 Documentation/media/kapi/dtv-frontend.rst diff --git a/Documentation/media/kapi/dtv-ca.rst b/Documentation/media/kapi/dtv-ca.rst new file mode 100644 index 000000000000..a4dd700189b0 --- /dev/null +++ b/Documentation/media/kapi/dtv-ca.rst @@ -0,0 +1,4 @@ +Digital TV Conditional Access kABI +---------------------------------- + +.. kernel-doc:: drivers/media/dvb-core/dvb_ca_en50221.h diff --git a/Documentation/media/kapi/dtv-common.rst b/Documentation/media/kapi/dtv-common.rst new file mode 100644 index 000000000000..40cf1033b5e1 --- /dev/null +++ b/Documentation/media/kapi/dtv-common.rst @@ -0,0 +1,55 @@ +Digital TV Common functions +--------------------------- + +Math functions +~~~~~~~~~~~~~~ + +Provide some commonly-used math functions, usually required in order to +estimate signal strength and signal to noise measurements in dB. + +.. kernel-doc:: drivers/media/dvb-core/dvb_math.h + + +DVB devices +~~~~~~~~~~~ + +Those functions are responsible for handling the DVB device nodes. + +.. kernel-doc:: drivers/media/dvb-core/dvbdev.h + +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 diff --git a/Documentation/media/kapi/dtv-core.rst b/Documentation/media/kapi/dtv-core.rst index 4cf9cf63bafd..8ee384f61fa0 100644 --- a/Documentation/media/kapi/dtv-core.rst +++ b/Documentation/media/kapi/dtv-core.rst @@ -26,584 +26,11 @@ I2C bus. abandoned standard, not used anymore) and ATSC version 3.0 current proposals. Currently, the DVB subsystem doesn't implement those standards. -Digital TV Common functions ---------------------------- -Math functions -~~~~~~~~~~~~~~ +.. toctree:: + :maxdepth: 1 -Provide some commonly-used math functions, usually required in order to -estimate signal strength and signal to noise measurements in dB. - -.. kernel-doc:: drivers/media/dvb-core/dvb_math.h - - -DVB devices -~~~~~~~~~~~ - -Those functions are responsible for handling the DVB device nodes. - -.. kernel-doc:: drivers/media/dvb-core/dvbdev.h - -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``. - -Demodulator driver -^^^^^^^^^^^^^^^^^^ - -The demodulator driver is responsible to talk with the decoding part of the -hardware. Such driver should implement :c:type:`dvb_frontend_ops`, with -tells what type of digital TV standards are supported, and points to a -series of functions that allow the DVB core to command the hardware via -the code under ``drivers/media/dvb-core/dvb_frontend.c``. - -A typical example of such struct in a driver ``foo`` is:: - - static struct dvb_frontend_ops foo_ops = { - .delsys = { SYS_DVBT, SYS_DVBT2, SYS_DVBC_ANNEX_A }, - .info = { - .name = "foo DVB-T/T2/C driver", - .caps = FE_CAN_FEC_1_2 | - FE_CAN_FEC_2_3 | - FE_CAN_FEC_3_4 | - FE_CAN_FEC_5_6 | - FE_CAN_FEC_7_8 | - FE_CAN_FEC_AUTO | - FE_CAN_QPSK | - FE_CAN_QAM_16 | - FE_CAN_QAM_32 | - FE_CAN_QAM_64 | - FE_CAN_QAM_128 | - FE_CAN_QAM_256 | - FE_CAN_QAM_AUTO | - FE_CAN_TRANSMISSION_MODE_AUTO | - FE_CAN_GUARD_INTERVAL_AUTO | - FE_CAN_HIERARCHY_AUTO | - FE_CAN_MUTE_TS | - FE_CAN_2G_MODULATION, - .frequency_min = 42000000, /* Hz */ - .frequency_max = 1002000000, /* Hz */ - .symbol_rate_min = 870000, - .symbol_rate_max = 11700000 - }, - .init = foo_init, - .sleep = foo_sleep, - .release = foo_release, - .set_frontend = foo_set_frontend, - .get_frontend = foo_get_frontend, - .read_status = foo_get_status_and_stats, - .tune = foo_tune, - .i2c_gate_ctrl = foo_i2c_gate_ctrl, - .get_frontend_algo = foo_get_algo, - }; - -A typical example of such struct in a driver ``bar`` meant to be used on -Satellite TV reception is:: - - static const struct dvb_frontend_ops bar_ops = { - .delsys = { SYS_DVBS, SYS_DVBS2 }, - .info = { - .name = "Bar DVB-S/S2 demodulator", - .frequency_min = 500000, /* KHz */ - .frequency_max = 2500000, /* KHz */ - .frequency_stepsize = 0, - .symbol_rate_min = 1000000, - .symbol_rate_max = 45000000, - .symbol_rate_tolerance = 500, - .caps = FE_CAN_INVERSION_AUTO | - FE_CAN_FEC_AUTO | - FE_CAN_QPSK, - }, - .init = bar_init, - .sleep = bar_sleep, - .release = bar_release, - .set_frontend = bar_set_frontend, - .get_frontend = bar_get_frontend, - .read_status = bar_get_status_and_stats, - .i2c_gate_ctrl = bar_i2c_gate_ctrl, - .get_frontend_algo = bar_get_algo, - .tune = bar_tune, - - /* Satellite-specific */ - .diseqc_send_master_cmd = bar_send_diseqc_msg, - .diseqc_send_burst = bar_send_burst, - .set_tone = bar_set_tone, - .set_voltage = bar_set_voltage, - }; - -.. note:: - - #) For satellite digital TV standards (DVB-S, DVB-S2, ISDB-S), the - frequencies are specified in kHz, while, for terrestrial and cable - standards, they're specified in Hz. Due to that, if the same frontend - supports both types, you'll need to have two separate - :c:type:`dvb_frontend_ops` structures, one for each standard. - #) The ``.i2c_gate_ctrl`` field is present only when the hardware has - allows controlling an I2C gate (either directly of via some GPIO pin), - in order to remove the tuner from the I2C bus after a channel is - tuned. - #) All new drivers should implement the - :ref:`DVBv5 statistics ` via ``.read_status``. - Yet, there are a number of callbacks meant to get statistics for - signal strength, S/N and UCB. Those are there to provide backward - compatibility with legacy applications that don't support the DVBv5 - API. Implementing those callbacks are optional. Those callbacks may be - removed in the future, after we have all existing drivers supporting - DVBv5 stats. - #) Other callbacks are required for satellite TV standards, in order to - control LNBf and DiSEqC: ``.diseqc_send_master_cmd``, - ``.diseqc_send_burst``, ``.set_tone``, ``.set_voltage``. - -.. |delta| unicode:: U+00394 - -The ``drivers/media/dvb-core/dvb_frontend.c`` has a kernel thread with is -responsible for tuning the device. It supports multiple algoritms to -detect a channel, as defined at enum :c:func:`dvbfe_algo`. - -The algorithm to be used is obtained via ``.get_frontend_algo``. If the driver -doesn't fill its field at struct :c:type:`dvb_frontend_ops`, it will default to -``DVBFE_ALGO_SW``, meaning that the dvb-core will do a zigzag when tuning, -e. g. it will try first to use the specified center frequency ``f``, -then, it will do ``f`` + |delta|, ``f`` - |delta|, ``f`` + 2 x |delta|, -``f`` - 2 x |delta| and so on. - -If the hardware has internally a some sort of zigzag algorithm, you should -define a ``.get_frontend_algo`` function that would return ``DVBFE_ALGO_HW``. - -.. note:: - - The core frontend support also supports - a third type (``DVBFE_ALGO_CUSTOM``), in order to allow the driver to - define its own hardware-assisted algorithm. Very few hardware need to - use it nowadays. Using ``DVBFE_ALGO_CUSTOM`` require to provide other - function callbacks at struct :c:type:`dvb_frontend_ops`. - -Attaching frontend driver to the bridge driver -^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ - -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. - -.. _dvbv5_stats: - -Digital TV Frontend statistics -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ - -Introduction -^^^^^^^^^^^^ - -Digital TV frontends provide a range of -:ref:`statistics ` meant to help tuning the device -and measuring the quality of service. - -For each statistics measurement, the driver should set the type of scale used, -or ``FE_SCALE_NOT_AVAILABLE`` if the statistics is not available on a given -time. Drivers should also provide the number of statistics for each type. -that's usually 1 for most video standards [#f2]_. - -Drivers should initialize each statistic counters with length and -scale at its init code. For example, if the frontend provides signal -strength, it should have, on its init code:: - - struct dtv_frontend_properties *c = &state->fe.dtv_property_cache; - - c->strength.len = 1; - c->strength.stat[0].scale = FE_SCALE_NOT_AVAILABLE; - -And, when the statistics got updated, set the scale:: - - c->strength.stat[0].scale = FE_SCALE_DECIBEL; - c->strength.stat[0].uvalue = strength; - -.. [#f2] For ISDB-T, it may provide both a global statistics and a per-layer - set of statistics. On such cases, len should be equal to 4. The first - value corresponds to the global stat; the other ones to each layer, e. g.: - - - c->cnr.stat[0] for global S/N carrier ratio, - - c->cnr.stat[1] for Layer A S/N carrier ratio, - - c->cnr.stat[2] for layer B S/N carrier ratio, - - c->cnr.stat[3] for layer C S/N carrier ratio. - -.. note:: Please prefer to use ``FE_SCALE_DECIBEL`` instead of - ``FE_SCALE_RELATIVE`` for signal strength and CNR measurements. - -Groups of statistics -^^^^^^^^^^^^^^^^^^^^ - -There are several groups of statistics currently supported: - -Signal strength (:ref:`DTV-STAT-SIGNAL-STRENGTH`) - - Measures the signal strength level at the analog part of the tuner or - demod. - - - Typically obtained from the gain applied to the tuner and/or frontend - in order to detect the carrier. When no carrier is detected, the gain is - at the maximum value (so, strength is on its minimal). - - - As the gain is visible through the set of registers that adjust the gain, - typically, this statistics is always available [#f3]_. - - - Drivers should try to make it available all the times, as this statistics - can be used when adjusting an antenna position and to check for troubles - at the cabling. - - .. [#f3] On a few devices, the gain keeps floating if no carrier. - On such devices, strength report should check first if carrier is - detected at the tuner (``FE_HAS_CARRIER``, see :c:type:`fe_status`), - and otherwise return the lowest possible value. - -Carrier Signal to Noise ratio (:ref:`DTV-STAT-CNR`) - - Signal to Noise ratio for the main carrier. - - - Signal to Noise measurement depends on the device. On some hardware, is - available when the main carrier is detected. On those hardware, CNR - measurement usually comes from the tuner (e. g. after ``FE_HAS_CARRIER``, - see :c:type:`fe_status`). - - On other devices, it requires inner FEC decoding, - as the frontend measures it indirectly from other parameters (e. g. after - ``FE_HAS_VITERBI``, see :c:type:`fe_status`). - - Having it available after inner FEC is more common. - -Bit counts post-FEC (:ref:`DTV-STAT-POST-ERROR-BIT-COUNT` and :ref:`DTV-STAT-POST-TOTAL-BIT-COUNT`) - - Those counters measure the number of bits and bit errors errors after - the forward error correction (FEC) on the inner coding block - (after Viterbi, LDPC or other inner code). - - - Due to its nature, those statistics depend on full coding lock - (e. g. after ``FE_HAS_SYNC`` or after ``FE_HAS_LOCK``, - see :c:type:`fe_status`). - -Bit counts pre-FEC (:ref:`DTV-STAT-PRE-ERROR-BIT-COUNT` and :ref:`DTV-STAT-PRE-TOTAL-BIT-COUNT`) - - Those counters measure the number of bits and bit errors errors before - the forward error correction (FEC) on the inner coding block - (before Viterbi, LDPC or other inner code). - - - Not all frontends provide this kind of statistics. - - - Due to its nature, those statistics depend on inner coding lock (e. g. - after ``FE_HAS_VITERBI``, see :c:type:`fe_status`). - -Block counts (:ref:`DTV-STAT-ERROR-BLOCK-COUNT` and :ref:`DTV-STAT-TOTAL-BLOCK-COUNT`) - - Those counters measure the number of blocks and block errors errors after - the forward error correction (FEC) on the inner coding block - (before Viterbi, LDPC or other inner code). - - - Due to its nature, those statistics depend on full coding lock - (e. g. after ``FE_HAS_SYNC`` or after - ``FE_HAS_LOCK``, see :c:type:`fe_status`). - -.. note:: All counters should be monotonically increased as they're - collected from the hardware. - -A typical example of the logic that handle status and statistics is:: - - static int foo_get_status_and_stats(struct dvb_frontend *fe) - { - struct foo_state *state = fe->demodulator_priv; - struct dtv_frontend_properties *c = &fe->dtv_property_cache; - - int rc; - enum fe_status *status; - - /* Both status and strength are always available */ - rc = foo_read_status(fe, &status); - if (rc < 0) - return rc; - - rc = foo_read_strength(fe); - if (rc < 0) - return rc; - - /* Check if CNR is available */ - if (!(fe->status & FE_HAS_CARRIER)) - return 0; - - rc = foo_read_cnr(fe); - if (rc < 0) - return rc; - - /* Check if pre-BER stats are available */ - if (!(fe->status & FE_HAS_VITERBI)) - return 0; - - rc = foo_get_pre_ber(fe); - if (rc < 0) - return rc; - - /* Check if post-BER stats are available */ - if (!(fe->status & FE_HAS_SYNC)) - return 0; - - rc = foo_get_post_ber(fe); - if (rc < 0) - return rc; - } - - static const struct dvb_frontend_ops ops = { - /* ... */ - .read_status = foo_get_status_and_stats, - }; - -Statistics collect -^^^^^^^^^^^^^^^^^^ - -On almost all frontend hardware, the bit and byte counts are stored by -the hardware after a certain amount of time or after the total bit/block -counter reaches a certain value (usually programable), for example, on -every 1000 ms or after receiving 1,000,000 bits. - -So, if you read the registers too soon, you'll end by reading the same -value as in the previous reading, causing the monotonic value to be -incremented too often. - -Drivers should take the responsibility to avoid too often reads. That -can be done using two approaches: - -if the driver have a bit that indicates when a collected data is ready -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% - -Driver should check such bit before making the statistics available. - -An example of such behavior can be found at this code snippet (adapted -from mb86a20s driver's logic):: - - static int foo_get_pre_ber(struct dvb_frontend *fe) - { - struct foo_state *state = fe->demodulator_priv; - struct dtv_frontend_properties *c = &fe->dtv_property_cache; - int rc, bit_error; - - /* Check if the BER measures are already available */ - rc = foo_read_u8(state, 0x54); - if (rc < 0) - return rc; - - if (!rc) - return 0; - - /* Read Bit Error Count */ - bit_error = foo_read_u32(state, 0x55); - if (bit_error < 0) - return bit_error; - - /* Read Total Bit Count */ - rc = foo_read_u32(state, 0x51); - if (rc < 0) - return rc; - - c->pre_bit_error.stat[0].scale = FE_SCALE_COUNTER; - c->pre_bit_error.stat[0].uvalue += bit_error; - c->pre_bit_count.stat[0].scale = FE_SCALE_COUNTER; - c->pre_bit_count.stat[0].uvalue += rc; - - return 0; - } - -If the driver doesn't provide a statistics available check bit -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% - -A few devices, however, may not provide a way to check if the stats are -available (or the way to check it is unknown). They may not even provide -a way to directly read the total number of bits or blocks. - -On those devices, the driver need to ensure that it won't be reading from -the register too often and/or estimate the total number of bits/blocks. - -On such drivers, a typical routine to get statistics would be like -(adapted from dib8000 driver's logic):: - - struct foo_state { - /* ... */ - - unsigned long per_jiffies_stats; - } - - static int foo_get_pre_ber(struct dvb_frontend *fe) - { - struct foo_state *state = fe->demodulator_priv; - struct dtv_frontend_properties *c = &fe->dtv_property_cache; - int rc, bit_error; - u64 bits; - - /* Check if time for stats was elapsed */ - if (!time_after(jiffies, state->per_jiffies_stats)) - return 0; - - /* Next stat should be collected in 1000 ms */ - state->per_jiffies_stats = jiffies + msecs_to_jiffies(1000); - - /* Read Bit Error Count */ - bit_error = foo_read_u32(state, 0x55); - if (bit_error < 0) - return bit_error; - - /* - * On this particular frontend, there's no register that - * would provide the number of bits per 1000ms sample. So, - * some function would calculate it based on DTV properties - */ - bits = get_number_of_bits_per_1000ms(fe); - - c->pre_bit_error.stat[0].scale = FE_SCALE_COUNTER; - c->pre_bit_error.stat[0].uvalue += bit_error; - c->pre_bit_count.stat[0].scale = FE_SCALE_COUNTER; - c->pre_bit_count.stat[0].uvalue += bits; - - return 0; - } - -Please notice that, on both cases, we're getting the statistics using the -:c:type:`dvb_frontend_ops` ``.read_status`` callback. The rationale is that -the frontend core will automatically call this function periodically -(usually, 3 times per second, when the frontend is locked). - -That warrants that we won't miss to collect a counter and increment the -monotonic stats at the right time. - -Digital TV Frontend functions and types -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ - -.. 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 + dtv-common + dtv-frontend + dtv-demux + dtv-ca diff --git a/Documentation/media/kapi/dtv-demux.rst b/Documentation/media/kapi/dtv-demux.rst new file mode 100644 index 000000000000..8169c479156e --- /dev/null +++ b/Documentation/media/kapi/dtv-demux.rst @@ -0,0 +1,71 @@ +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 +~~~~~~~~~~~~~~~~~~ + +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 diff --git a/Documentation/media/kapi/dtv-frontend.rst b/Documentation/media/kapi/dtv-frontend.rst new file mode 100644 index 000000000000..9f67b7a7387d --- /dev/null +++ b/Documentation/media/kapi/dtv-frontend.rst @@ -0,0 +1,443 @@ +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``. + +Demodulator driver +^^^^^^^^^^^^^^^^^^ + +The demodulator driver is responsible to talk with the decoding part of the +hardware. Such driver should implement :c:type:`dvb_frontend_ops`, with +tells what type of digital TV standards are supported, and points to a +series of functions that allow the DVB core to command the hardware via +the code under ``drivers/media/dvb-core/dvb_frontend.c``. + +A typical example of such struct in a driver ``foo`` is:: + + static struct dvb_frontend_ops foo_ops = { + .delsys = { SYS_DVBT, SYS_DVBT2, SYS_DVBC_ANNEX_A }, + .info = { + .name = "foo DVB-T/T2/C driver", + .caps = FE_CAN_FEC_1_2 | + FE_CAN_FEC_2_3 | + FE_CAN_FEC_3_4 | + FE_CAN_FEC_5_6 | + FE_CAN_FEC_7_8 | + FE_CAN_FEC_AUTO | + FE_CAN_QPSK | + FE_CAN_QAM_16 | + FE_CAN_QAM_32 | + FE_CAN_QAM_64 | + FE_CAN_QAM_128 | + FE_CAN_QAM_256 | + FE_CAN_QAM_AUTO | + FE_CAN_TRANSMISSION_MODE_AUTO | + FE_CAN_GUARD_INTERVAL_AUTO | + FE_CAN_HIERARCHY_AUTO | + FE_CAN_MUTE_TS | + FE_CAN_2G_MODULATION, + .frequency_min = 42000000, /* Hz */ + .frequency_max = 1002000000, /* Hz */ + .symbol_rate_min = 870000, + .symbol_rate_max = 11700000 + }, + .init = foo_init, + .sleep = foo_sleep, + .release = foo_release, + .set_frontend = foo_set_frontend, + .get_frontend = foo_get_frontend, + .read_status = foo_get_status_and_stats, + .tune = foo_tune, + .i2c_gate_ctrl = foo_i2c_gate_ctrl, + .get_frontend_algo = foo_get_algo, + }; + +A typical example of such struct in a driver ``bar`` meant to be used on +Satellite TV reception is:: + + static const struct dvb_frontend_ops bar_ops = { + .delsys = { SYS_DVBS, SYS_DVBS2 }, + .info = { + .name = "Bar DVB-S/S2 demodulator", + .frequency_min = 500000, /* KHz */ + .frequency_max = 2500000, /* KHz */ + .frequency_stepsize = 0, + .symbol_rate_min = 1000000, + .symbol_rate_max = 45000000, + .symbol_rate_tolerance = 500, + .caps = FE_CAN_INVERSION_AUTO | + FE_CAN_FEC_AUTO | + FE_CAN_QPSK, + }, + .init = bar_init, + .sleep = bar_sleep, + .release = bar_release, + .set_frontend = bar_set_frontend, + .get_frontend = bar_get_frontend, + .read_status = bar_get_status_and_stats, + .i2c_gate_ctrl = bar_i2c_gate_ctrl, + .get_frontend_algo = bar_get_algo, + .tune = bar_tune, + + /* Satellite-specific */ + .diseqc_send_master_cmd = bar_send_diseqc_msg, + .diseqc_send_burst = bar_send_burst, + .set_tone = bar_set_tone, + .set_voltage = bar_set_voltage, + }; + +.. note:: + + #) For satellite digital TV standards (DVB-S, DVB-S2, ISDB-S), the + frequencies are specified in kHz, while, for terrestrial and cable + standards, they're specified in Hz. Due to that, if the same frontend + supports both types, you'll need to have two separate + :c:type:`dvb_frontend_ops` structures, one for each standard. + #) The ``.i2c_gate_ctrl`` field is present only when the hardware has + allows controlling an I2C gate (either directly of via some GPIO pin), + in order to remove the tuner from the I2C bus after a channel is + tuned. + #) All new drivers should implement the + :ref:`DVBv5 statistics ` via ``.read_status``. + Yet, there are a number of callbacks meant to get statistics for + signal strength, S/N and UCB. Those are there to provide backward + compatibility with legacy applications that don't support the DVBv5 + API. Implementing those callbacks are optional. Those callbacks may be + removed in the future, after we have all existing drivers supporting + DVBv5 stats. + #) Other callbacks are required for satellite TV standards, in order to + control LNBf and DiSEqC: ``.diseqc_send_master_cmd``, + ``.diseqc_send_burst``, ``.set_tone``, ``.set_voltage``. + +.. |delta| unicode:: U+00394 + +The ``drivers/media/dvb-core/dvb_frontend.c`` has a kernel thread with is +responsible for tuning the device. It supports multiple algoritms to +detect a channel, as defined at enum :c:func:`dvbfe_algo`. + +The algorithm to be used is obtained via ``.get_frontend_algo``. If the driver +doesn't fill its field at struct :c:type:`dvb_frontend_ops`, it will default to +``DVBFE_ALGO_SW``, meaning that the dvb-core will do a zigzag when tuning, +e. g. it will try first to use the specified center frequency ``f``, +then, it will do ``f`` + |delta|, ``f`` - |delta|, ``f`` + 2 x |delta|, +``f`` - 2 x |delta| and so on. + +If the hardware has internally a some sort of zigzag algorithm, you should +define a ``.get_frontend_algo`` function that would return ``DVBFE_ALGO_HW``. + +.. note:: + + The core frontend support also supports + a third type (``DVBFE_ALGO_CUSTOM``), in order to allow the driver to + define its own hardware-assisted algorithm. Very few hardware need to + use it nowadays. Using ``DVBFE_ALGO_CUSTOM`` require to provide other + function callbacks at struct :c:type:`dvb_frontend_ops`. + +Attaching frontend driver to the bridge driver +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +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. + +.. _dvbv5_stats: + +Digital TV Frontend statistics +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Introduction +^^^^^^^^^^^^ + +Digital TV frontends provide a range of +:ref:`statistics ` meant to help tuning the device +and measuring the quality of service. + +For each statistics measurement, the driver should set the type of scale used, +or ``FE_SCALE_NOT_AVAILABLE`` if the statistics is not available on a given +time. Drivers should also provide the number of statistics for each type. +that's usually 1 for most video standards [#f2]_. + +Drivers should initialize each statistic counters with length and +scale at its init code. For example, if the frontend provides signal +strength, it should have, on its init code:: + + struct dtv_frontend_properties *c = &state->fe.dtv_property_cache; + + c->strength.len = 1; + c->strength.stat[0].scale = FE_SCALE_NOT_AVAILABLE; + +And, when the statistics got updated, set the scale:: + + c->strength.stat[0].scale = FE_SCALE_DECIBEL; + c->strength.stat[0].uvalue = strength; + +.. [#f2] For ISDB-T, it may provide both a global statistics and a per-layer + set of statistics. On such cases, len should be equal to 4. The first + value corresponds to the global stat; the other ones to each layer, e. g.: + + - c->cnr.stat[0] for global S/N carrier ratio, + - c->cnr.stat[1] for Layer A S/N carrier ratio, + - c->cnr.stat[2] for layer B S/N carrier ratio, + - c->cnr.stat[3] for layer C S/N carrier ratio. + +.. note:: Please prefer to use ``FE_SCALE_DECIBEL`` instead of + ``FE_SCALE_RELATIVE`` for signal strength and CNR measurements. + +Groups of statistics +^^^^^^^^^^^^^^^^^^^^ + +There are several groups of statistics currently supported: + +Signal strength (:ref:`DTV-STAT-SIGNAL-STRENGTH`) + - Measures the signal strength level at the analog part of the tuner or + demod. + + - Typically obtained from the gain applied to the tuner and/or frontend + in order to detect the carrier. When no carrier is detected, the gain is + at the maximum value (so, strength is on its minimal). + + - As the gain is visible through the set of registers that adjust the gain, + typically, this statistics is always available [#f3]_. + + - Drivers should try to make it available all the times, as this statistics + can be used when adjusting an antenna position and to check for troubles + at the cabling. + + .. [#f3] On a few devices, the gain keeps floating if no carrier. + On such devices, strength report should check first if carrier is + detected at the tuner (``FE_HAS_CARRIER``, see :c:type:`fe_status`), + and otherwise return the lowest possible value. + +Carrier Signal to Noise ratio (:ref:`DTV-STAT-CNR`) + - Signal to Noise ratio for the main carrier. + + - Signal to Noise measurement depends on the device. On some hardware, is + available when the main carrier is detected. On those hardware, CNR + measurement usually comes from the tuner (e. g. after ``FE_HAS_CARRIER``, + see :c:type:`fe_status`). + + On other devices, it requires inner FEC decoding, + as the frontend measures it indirectly from other parameters (e. g. after + ``FE_HAS_VITERBI``, see :c:type:`fe_status`). + + Having it available after inner FEC is more common. + +Bit counts post-FEC (:ref:`DTV-STAT-POST-ERROR-BIT-COUNT` and :ref:`DTV-STAT-POST-TOTAL-BIT-COUNT`) + - Those counters measure the number of bits and bit errors errors after + the forward error correction (FEC) on the inner coding block + (after Viterbi, LDPC or other inner code). + + - Due to its nature, those statistics depend on full coding lock + (e. g. after ``FE_HAS_SYNC`` or after ``FE_HAS_LOCK``, + see :c:type:`fe_status`). + +Bit counts pre-FEC (:ref:`DTV-STAT-PRE-ERROR-BIT-COUNT` and :ref:`DTV-STAT-PRE-TOTAL-BIT-COUNT`) + - Those counters measure the number of bits and bit errors errors before + the forward error correction (FEC) on the inner coding block + (before Viterbi, LDPC or other inner code). + + - Not all frontends provide this kind of statistics. + + - Due to its nature, those statistics depend on inner coding lock (e. g. + after ``FE_HAS_VITERBI``, see :c:type:`fe_status`). + +Block counts (:ref:`DTV-STAT-ERROR-BLOCK-COUNT` and :ref:`DTV-STAT-TOTAL-BLOCK-COUNT`) + - Those counters measure the number of blocks and block errors errors after + the forward error correction (FEC) on the inner coding block + (before Viterbi, LDPC or other inner code). + + - Due to its nature, those statistics depend on full coding lock + (e. g. after ``FE_HAS_SYNC`` or after + ``FE_HAS_LOCK``, see :c:type:`fe_status`). + +.. note:: All counters should be monotonically increased as they're + collected from the hardware. + +A typical example of the logic that handle status and statistics is:: + + static int foo_get_status_and_stats(struct dvb_frontend *fe) + { + struct foo_state *state = fe->demodulator_priv; + struct dtv_frontend_properties *c = &fe->dtv_property_cache; + + int rc; + enum fe_status *status; + + /* Both status and strength are always available */ + rc = foo_read_status(fe, &status); + if (rc < 0) + return rc; + + rc = foo_read_strength(fe); + if (rc < 0) + return rc; + + /* Check if CNR is available */ + if (!(fe->status & FE_HAS_CARRIER)) + return 0; + + rc = foo_read_cnr(fe); + if (rc < 0) + return rc; + + /* Check if pre-BER stats are available */ + if (!(fe->status & FE_HAS_VITERBI)) + return 0; + + rc = foo_get_pre_ber(fe); + if (rc < 0) + return rc; + + /* Check if post-BER stats are available */ + if (!(fe->status & FE_HAS_SYNC)) + return 0; + + rc = foo_get_post_ber(fe); + if (rc < 0) + return rc; + } + + static const struct dvb_frontend_ops ops = { + /* ... */ + .read_status = foo_get_status_and_stats, + }; + +Statistics collect +^^^^^^^^^^^^^^^^^^ + +On almost all frontend hardware, the bit and byte counts are stored by +the hardware after a certain amount of time or after the total bit/block +counter reaches a certain value (usually programable), for example, on +every 1000 ms or after receiving 1,000,000 bits. + +So, if you read the registers too soon, you'll end by reading the same +value as in the previous reading, causing the monotonic value to be +incremented too often. + +Drivers should take the responsibility to avoid too often reads. That +can be done using two approaches: + +if the driver have a bit that indicates when a collected data is ready +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% + +Driver should check such bit before making the statistics available. + +An example of such behavior can be found at this code snippet (adapted +from mb86a20s driver's logic):: + + static int foo_get_pre_ber(struct dvb_frontend *fe) + { + struct foo_state *state = fe->demodulator_priv; + struct dtv_frontend_properties *c = &fe->dtv_property_cache; + int rc, bit_error; + + /* Check if the BER measures are already available */ + rc = foo_read_u8(state, 0x54); + if (rc < 0) + return rc; + + if (!rc) + return 0; + + /* Read Bit Error Count */ + bit_error = foo_read_u32(state, 0x55); + if (bit_error < 0) + return bit_error; + + /* Read Total Bit Count */ + rc = foo_read_u32(state, 0x51); + if (rc < 0) + return rc; + + c->pre_bit_error.stat[0].scale = FE_SCALE_COUNTER; + c->pre_bit_error.stat[0].uvalue += bit_error; + c->pre_bit_count.stat[0].scale = FE_SCALE_COUNTER; + c->pre_bit_count.stat[0].uvalue += rc; + + return 0; + } + +If the driver doesn't provide a statistics available check bit +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% + +A few devices, however, may not provide a way to check if the stats are +available (or the way to check it is unknown). They may not even provide +a way to directly read the total number of bits or blocks. + +On those devices, the driver need to ensure that it won't be reading from +the register too often and/or estimate the total number of bits/blocks. + +On such drivers, a typical routine to get statistics would be like +(adapted from dib8000 driver's logic):: + + struct foo_state { + /* ... */ + + unsigned long per_jiffies_stats; + } + + static int foo_get_pre_ber(struct dvb_frontend *fe) + { + struct foo_state *state = fe->demodulator_priv; + struct dtv_frontend_properties *c = &fe->dtv_property_cache; + int rc, bit_error; + u64 bits; + + /* Check if time for stats was elapsed */ + if (!time_after(jiffies, state->per_jiffies_stats)) + return 0; + + /* Next stat should be collected in 1000 ms */ + state->per_jiffies_stats = jiffies + msecs_to_jiffies(1000); + + /* Read Bit Error Count */ + bit_error = foo_read_u32(state, 0x55); + if (bit_error < 0) + return bit_error; + + /* + * On this particular frontend, there's no register that + * would provide the number of bits per 1000ms sample. So, + * some function would calculate it based on DTV properties + */ + bits = get_number_of_bits_per_1000ms(fe); + + c->pre_bit_error.stat[0].scale = FE_SCALE_COUNTER; + c->pre_bit_error.stat[0].uvalue += bit_error; + c->pre_bit_count.stat[0].scale = FE_SCALE_COUNTER; + c->pre_bit_count.stat[0].uvalue += bits; + + return 0; + } + +Please notice that, on both cases, we're getting the statistics using the +:c:type:`dvb_frontend_ops` ``.read_status`` callback. The rationale is that +the frontend core will automatically call this function periodically +(usually, 3 times per second, when the frontend is locked). + +That warrants that we won't miss to collect a counter and increment the +monotonic stats at the right time. + +Digital TV Frontend functions and types +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +.. kernel-doc:: drivers/media/dvb-core/dvb_frontend.h -- 2.39.2