forked from luck/tmp_suning_uos_patched
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 <mchehab@s-opensource.com>
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4
Documentation/media/kapi/dtv-ca.rst
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4
Documentation/media/kapi/dtv-ca.rst
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@ -0,0 +1,4 @@
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Digital TV Conditional Access kABI
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----------------------------------
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.. kernel-doc:: drivers/media/dvb-core/dvb_ca_en50221.h
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55
Documentation/media/kapi/dtv-common.rst
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55
Documentation/media/kapi/dtv-common.rst
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@ -0,0 +1,55 @@
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Digital TV Common functions
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---------------------------
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Math functions
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~~~~~~~~~~~~~~
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Provide some commonly-used math functions, usually required in order to
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estimate signal strength and signal to noise measurements in dB.
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.. kernel-doc:: drivers/media/dvb-core/dvb_math.h
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DVB devices
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~~~~~~~~~~~
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Those functions are responsible for handling the DVB device nodes.
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.. kernel-doc:: drivers/media/dvb-core/dvbdev.h
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Digital TV Ring buffer
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~~~~~~~~~~~~~~~~~~~~~~
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Those routines implement ring buffers used to handle digital TV data and
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copy it from/to userspace.
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.. note::
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1) For performance reasons read and write routines don't check buffer sizes
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and/or number of bytes free/available. This has to be done before these
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routines are called. For example:
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.. code-block:: c
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/* write @buflen: bytes */
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free = dvb_ringbuffer_free(rbuf);
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if (free >= buflen)
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count = dvb_ringbuffer_write(rbuf, buffer, buflen);
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else
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/* do something */
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/* read min. 1000, max. @bufsize: bytes */
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avail = dvb_ringbuffer_avail(rbuf);
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if (avail >= 1000)
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count = dvb_ringbuffer_read(rbuf, buffer, min(avail, bufsize));
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else
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/* do something */
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2) If there is exactly one reader and one writer, there is no need
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to lock read or write operations.
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Two or more readers must be locked against each other.
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Flushing the buffer counts as a read operation.
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Resetting the buffer counts as a read and write operation.
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Two or more writers must be locked against each other.
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.. kernel-doc:: drivers/media/dvb-core/dvb_ringbuffer.h
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@ -26,584 +26,11 @@ I2C bus.
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abandoned standard, not used anymore) and ATSC version 3.0 current
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proposals. Currently, the DVB subsystem doesn't implement those standards.
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Digital TV Common functions
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---------------------------
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Math functions
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~~~~~~~~~~~~~~
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.. toctree::
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:maxdepth: 1
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Provide some commonly-used math functions, usually required in order to
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estimate signal strength and signal to noise measurements in dB.
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.. kernel-doc:: drivers/media/dvb-core/dvb_math.h
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DVB devices
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~~~~~~~~~~~
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Those functions are responsible for handling the DVB device nodes.
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.. kernel-doc:: drivers/media/dvb-core/dvbdev.h
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Digital TV Ring buffer
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----------------------
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Those routines implement ring buffers used to handle digital TV data and
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copy it from/to userspace.
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.. note::
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1) For performance reasons read and write routines don't check buffer sizes
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and/or number of bytes free/available. This has to be done before these
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routines are called. For example:
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.. code-block:: c
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/* write @buflen: bytes */
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free = dvb_ringbuffer_free(rbuf);
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if (free >= buflen)
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count = dvb_ringbuffer_write(rbuf, buffer, buflen);
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else
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/* do something */
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/* read min. 1000, max. @bufsize: bytes */
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avail = dvb_ringbuffer_avail(rbuf);
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if (avail >= 1000)
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count = dvb_ringbuffer_read(rbuf, buffer, min(avail, bufsize));
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else
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/* do something */
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2) If there is exactly one reader and one writer, there is no need
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to lock read or write operations.
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Two or more readers must be locked against each other.
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Flushing the buffer counts as a read operation.
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Resetting the buffer counts as a read and write operation.
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Two or more writers must be locked against each other.
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.. kernel-doc:: drivers/media/dvb-core/dvb_ringbuffer.h
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Digital TV Frontend kABI
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------------------------
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Digital TV Frontend
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~~~~~~~~~~~~~~~~~~~
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The Digital TV Frontend kABI defines a driver-internal interface for
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registering low-level, hardware specific driver to a hardware independent
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frontend layer. It is only of interest for Digital TV device driver writers.
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The header file for this API is named ``dvb_frontend.h`` and located in
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``drivers/media/dvb-core``.
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Demodulator driver
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^^^^^^^^^^^^^^^^^^
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The demodulator driver is responsible to talk with the decoding part of the
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hardware. Such driver should implement :c:type:`dvb_frontend_ops`, with
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tells what type of digital TV standards are supported, and points to a
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series of functions that allow the DVB core to command the hardware via
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the code under ``drivers/media/dvb-core/dvb_frontend.c``.
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A typical example of such struct in a driver ``foo`` is::
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static struct dvb_frontend_ops foo_ops = {
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.delsys = { SYS_DVBT, SYS_DVBT2, SYS_DVBC_ANNEX_A },
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.info = {
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.name = "foo DVB-T/T2/C driver",
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.caps = FE_CAN_FEC_1_2 |
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FE_CAN_FEC_2_3 |
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FE_CAN_FEC_3_4 |
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FE_CAN_FEC_5_6 |
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FE_CAN_FEC_7_8 |
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FE_CAN_FEC_AUTO |
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FE_CAN_QPSK |
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FE_CAN_QAM_16 |
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FE_CAN_QAM_32 |
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FE_CAN_QAM_64 |
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FE_CAN_QAM_128 |
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FE_CAN_QAM_256 |
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FE_CAN_QAM_AUTO |
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FE_CAN_TRANSMISSION_MODE_AUTO |
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FE_CAN_GUARD_INTERVAL_AUTO |
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FE_CAN_HIERARCHY_AUTO |
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FE_CAN_MUTE_TS |
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FE_CAN_2G_MODULATION,
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.frequency_min = 42000000, /* Hz */
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.frequency_max = 1002000000, /* Hz */
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.symbol_rate_min = 870000,
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.symbol_rate_max = 11700000
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},
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.init = foo_init,
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.sleep = foo_sleep,
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.release = foo_release,
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.set_frontend = foo_set_frontend,
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.get_frontend = foo_get_frontend,
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.read_status = foo_get_status_and_stats,
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.tune = foo_tune,
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.i2c_gate_ctrl = foo_i2c_gate_ctrl,
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.get_frontend_algo = foo_get_algo,
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};
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A typical example of such struct in a driver ``bar`` meant to be used on
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Satellite TV reception is::
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static const struct dvb_frontend_ops bar_ops = {
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.delsys = { SYS_DVBS, SYS_DVBS2 },
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.info = {
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.name = "Bar DVB-S/S2 demodulator",
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.frequency_min = 500000, /* KHz */
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.frequency_max = 2500000, /* KHz */
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.frequency_stepsize = 0,
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.symbol_rate_min = 1000000,
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.symbol_rate_max = 45000000,
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.symbol_rate_tolerance = 500,
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.caps = FE_CAN_INVERSION_AUTO |
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FE_CAN_FEC_AUTO |
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FE_CAN_QPSK,
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},
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.init = bar_init,
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.sleep = bar_sleep,
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.release = bar_release,
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.set_frontend = bar_set_frontend,
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.get_frontend = bar_get_frontend,
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.read_status = bar_get_status_and_stats,
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.i2c_gate_ctrl = bar_i2c_gate_ctrl,
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.get_frontend_algo = bar_get_algo,
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.tune = bar_tune,
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/* Satellite-specific */
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.diseqc_send_master_cmd = bar_send_diseqc_msg,
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.diseqc_send_burst = bar_send_burst,
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.set_tone = bar_set_tone,
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.set_voltage = bar_set_voltage,
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};
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.. note::
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#) For satellite digital TV standards (DVB-S, DVB-S2, ISDB-S), the
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frequencies are specified in kHz, while, for terrestrial and cable
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standards, they're specified in Hz. Due to that, if the same frontend
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supports both types, you'll need to have two separate
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:c:type:`dvb_frontend_ops` structures, one for each standard.
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#) The ``.i2c_gate_ctrl`` field is present only when the hardware has
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allows controlling an I2C gate (either directly of via some GPIO pin),
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in order to remove the tuner from the I2C bus after a channel is
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tuned.
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#) All new drivers should implement the
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:ref:`DVBv5 statistics <dvbv5_stats>` via ``.read_status``.
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Yet, there are a number of callbacks meant to get statistics for
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signal strength, S/N and UCB. Those are there to provide backward
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compatibility with legacy applications that don't support the DVBv5
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API. Implementing those callbacks are optional. Those callbacks may be
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removed in the future, after we have all existing drivers supporting
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DVBv5 stats.
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#) Other callbacks are required for satellite TV standards, in order to
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control LNBf and DiSEqC: ``.diseqc_send_master_cmd``,
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``.diseqc_send_burst``, ``.set_tone``, ``.set_voltage``.
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.. |delta| unicode:: U+00394
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The ``drivers/media/dvb-core/dvb_frontend.c`` has a kernel thread with is
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responsible for tuning the device. It supports multiple algoritms to
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detect a channel, as defined at enum :c:func:`dvbfe_algo`.
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The algorithm to be used is obtained via ``.get_frontend_algo``. If the driver
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doesn't fill its field at struct :c:type:`dvb_frontend_ops`, it will default to
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``DVBFE_ALGO_SW``, meaning that the dvb-core will do a zigzag when tuning,
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e. g. it will try first to use the specified center frequency ``f``,
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then, it will do ``f`` + |delta|, ``f`` - |delta|, ``f`` + 2 x |delta|,
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``f`` - 2 x |delta| and so on.
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If the hardware has internally a some sort of zigzag algorithm, you should
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define a ``.get_frontend_algo`` function that would return ``DVBFE_ALGO_HW``.
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.. note::
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The core frontend support also supports
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a third type (``DVBFE_ALGO_CUSTOM``), in order to allow the driver to
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define its own hardware-assisted algorithm. Very few hardware need to
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use it nowadays. Using ``DVBFE_ALGO_CUSTOM`` require to provide other
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function callbacks at struct :c:type:`dvb_frontend_ops`.
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Attaching frontend driver to the bridge driver
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Before using the Digital TV frontend core, the bridge driver should attach
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the frontend demod, tuner and SEC devices and call
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:c:func:`dvb_register_frontend()`,
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in order to register the new frontend at the subsystem. At device
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detach/removal, the bridge driver should call
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:c:func:`dvb_unregister_frontend()` to
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remove the frontend from the core and then :c:func:`dvb_frontend_detach()`
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to free the memory allocated by the frontend drivers.
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The drivers should also call :c:func:`dvb_frontend_suspend()` as part of
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their handler for the :c:type:`device_driver`.\ ``suspend()``, and
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:c:func:`dvb_frontend_resume()` as
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part of their handler for :c:type:`device_driver`.\ ``resume()``.
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A few other optional functions are provided to handle some special cases.
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.. _dvbv5_stats:
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Digital TV Frontend statistics
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Introduction
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^^^^^^^^^^^^
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Digital TV frontends provide a range of
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:ref:`statistics <frontend-stat-properties>` meant to help tuning the device
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and measuring the quality of service.
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For each statistics measurement, the driver should set the type of scale used,
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or ``FE_SCALE_NOT_AVAILABLE`` if the statistics is not available on a given
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time. Drivers should also provide the number of statistics for each type.
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that's usually 1 for most video standards [#f2]_.
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Drivers should initialize each statistic counters with length and
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scale at its init code. For example, if the frontend provides signal
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strength, it should have, on its init code::
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struct dtv_frontend_properties *c = &state->fe.dtv_property_cache;
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c->strength.len = 1;
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c->strength.stat[0].scale = FE_SCALE_NOT_AVAILABLE;
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And, when the statistics got updated, set the scale::
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c->strength.stat[0].scale = FE_SCALE_DECIBEL;
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c->strength.stat[0].uvalue = strength;
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.. [#f2] For ISDB-T, it may provide both a global statistics and a per-layer
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set of statistics. On such cases, len should be equal to 4. The first
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value corresponds to the global stat; the other ones to each layer, e. g.:
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- c->cnr.stat[0] for global S/N carrier ratio,
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- c->cnr.stat[1] for Layer A S/N carrier ratio,
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- c->cnr.stat[2] for layer B S/N carrier ratio,
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- c->cnr.stat[3] for layer C S/N carrier ratio.
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.. note:: Please prefer to use ``FE_SCALE_DECIBEL`` instead of
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``FE_SCALE_RELATIVE`` for signal strength and CNR measurements.
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Groups of statistics
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^^^^^^^^^^^^^^^^^^^^
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There are several groups of statistics currently supported:
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Signal strength (:ref:`DTV-STAT-SIGNAL-STRENGTH`)
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- Measures the signal strength level at the analog part of the tuner or
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demod.
|
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|
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- Typically obtained from the gain applied to the tuner and/or frontend
|
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in order to detect the carrier. When no carrier is detected, the gain is
|
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at the maximum value (so, strength is on its minimal).
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|
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- As the gain is visible through the set of registers that adjust the gain,
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typically, this statistics is always available [#f3]_.
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|
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- Drivers should try to make it available all the times, as this statistics
|
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can be used when adjusting an antenna position and to check for troubles
|
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at the cabling.
|
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|
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.. [#f3] On a few devices, the gain keeps floating if no carrier.
|
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On such devices, strength report should check first if carrier is
|
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detected at the tuner (``FE_HAS_CARRIER``, see :c:type:`fe_status`),
|
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and otherwise return the lowest possible value.
|
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|
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Carrier Signal to Noise ratio (:ref:`DTV-STAT-CNR`)
|
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- Signal to Noise ratio for the main carrier.
|
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|
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- Signal to Noise measurement depends on the device. On some hardware, is
|
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available when the main carrier is detected. On those hardware, CNR
|
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measurement usually comes from the tuner (e. g. after ``FE_HAS_CARRIER``,
|
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see :c:type:`fe_status`).
|
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|
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On other devices, it requires inner FEC decoding,
|
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as the frontend measures it indirectly from other parameters (e. g. after
|
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``FE_HAS_VITERBI``, see :c:type:`fe_status`).
|
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|
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Having it available after inner FEC is more common.
|
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|
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Bit counts post-FEC (:ref:`DTV-STAT-POST-ERROR-BIT-COUNT` and :ref:`DTV-STAT-POST-TOTAL-BIT-COUNT`)
|
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- Those counters measure the number of bits and bit errors errors after
|
||||
the forward error correction (FEC) on the inner coding block
|
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(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`).
|
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|
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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
|
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the forward error correction (FEC) on the inner coding block
|
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(before Viterbi, LDPC or other inner code).
|
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|
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- 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`)
|
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- 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`).
|
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|
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.. note:: All counters should be monotonically increased as they're
|
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collected from the hardware.
|
||||
|
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A typical example of the logic that handle status and statistics is::
|
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|
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static int foo_get_status_and_stats(struct dvb_frontend *fe)
|
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{
|
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struct foo_state *state = fe->demodulator_priv;
|
||||
struct dtv_frontend_properties *c = &fe->dtv_property_cache;
|
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|
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int rc;
|
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enum fe_status *status;
|
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|
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/* Both status and strength are always available */
|
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rc = foo_read_status(fe, &status);
|
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if (rc < 0)
|
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return rc;
|
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|
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rc = foo_read_strength(fe);
|
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if (rc < 0)
|
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return rc;
|
||||
|
||||
/* Check if CNR is available */
|
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if (!(fe->status & FE_HAS_CARRIER))
|
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return 0;
|
||||
|
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rc = foo_read_cnr(fe);
|
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if (rc < 0)
|
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return rc;
|
||||
|
||||
/* Check if pre-BER stats are available */
|
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if (!(fe->status & FE_HAS_VITERBI))
|
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return 0;
|
||||
|
||||
rc = foo_get_pre_ber(fe);
|
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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
|
||||
|
|
|
|||
71
Documentation/media/kapi/dtv-demux.rst
Normal file
71
Documentation/media/kapi/dtv-demux.rst
Normal file
|
|
@ -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
|
||||
443
Documentation/media/kapi/dtv-frontend.rst
Normal file
443
Documentation/media/kapi/dtv-frontend.rst
Normal file
|
|
@ -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 <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 ``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 <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 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
|
||||
Loading…
Reference in New Issue
Block a user