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+.. SPDX-License-Identifier: GPL-2.0
+
+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
+``include/media/``.
+
+Demodulator driver
+^^^^^^^^^^^^^^^^^^
+
+The demodulator driver is responsible for talking with the decoding part of the
+hardware. Such driver should implement :c:type:`dvb_frontend_ops`, which
+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 ``include/media/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 <dvbv5_stats>` 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 ``include/media/dvb_frontend.c`` has a kernel thread which is
+responsible for tuning the device. It supports multiple algorithms 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 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 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 <frontend-stat-properties>` 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 these 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 there is 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, it 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 collection
+^^^^^^^^^^^^^^^^^^^^^
+
+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 programmable), 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:: include/media/dvb_frontend.h
generated by cgit v1.2.3 (git 2.39.1) at 2024-11-06 07:13:54 +0000