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1=========================2Audio Stream in SoundWire3=========================4 5An audio stream is a logical or virtual connection created between6 7 (1) System memory buffer(s) and Codec(s)8 9 (2) DSP memory buffer(s) and Codec(s)10 11 (3) FIFO(s) and Codec(s)12 13 (4) Codec(s) and Codec(s)14 15which is typically driven by a DMA(s) channel through the data link. An16audio stream contains one or more channels of data. All channels within17stream must have same sample rate and same sample size.18 19Assume a stream with two channels (Left & Right) is opened using SoundWire20interface. Below are some ways a stream can be represented in SoundWire.21 22Stream Sample in memory (System memory, DSP memory or FIFOs) ::23 24 -------------------------25 | L | R | L | R | L | R |26 -------------------------27 28Example 1: Stereo Stream with L and R channels is rendered from Master to29Slave. Both Master and Slave is using single port. ::30 31 +---------------+ Clock Signal +---------------+32 | Master +----------------------------------+ Slave |33 | Interface | | Interface |34 | | | 1 |35 | | Data Signal | |36 | L + R +----------------------------------+ L + R |37 | (Data) | Data Direction | (Data) |38 +---------------+ +-----------------------> +---------------+39 40 41Example 2: Stereo Stream with L and R channels is captured from Slave to42Master. Both Master and Slave is using single port. ::43 44 45 +---------------+ Clock Signal +---------------+46 | Master +----------------------------------+ Slave |47 | Interface | | Interface |48 | | | 1 |49 | | Data Signal | |50 | L + R +----------------------------------+ L + R |51 | (Data) | Data Direction | (Data) |52 +---------------+ <-----------------------+ +---------------+53 54 55Example 3: Stereo Stream with L and R channels is rendered by Master. Each56of the L and R channel is received by two different Slaves. Master and both57Slaves are using single port. ::58 59 +---------------+ Clock Signal +---------------+60 | Master +---------+------------------------+ Slave |61 | Interface | | | Interface |62 | | | | 1 |63 | | | Data Signal | |64 | L + R +---+------------------------------+ L |65 | (Data) | | | Data Direction | (Data) |66 +---------------+ | | +-------------> +---------------+67 | |68 | |69 | | +---------------+70 | +----------------------> | Slave |71 | | Interface |72 | | 2 |73 | | |74 +----------------------------> | R |75 | (Data) |76 +---------------+77 78Example 4: Stereo Stream with L and R channels is rendered by79Master. Both of the L and R channels are received by two different80Slaves. Master and both Slaves are using single port handling81L+R. Each Slave device processes the L + R data locally, typically82based on static configuration or dynamic orientation, and may drive83one or more speakers. ::84 85 +---------------+ Clock Signal +---------------+86 | Master +---------+------------------------+ Slave |87 | Interface | | | Interface |88 | | | | 1 |89 | | | Data Signal | |90 | L + R +---+------------------------------+ L + R |91 | (Data) | | | Data Direction | (Data) |92 +---------------+ | | +-------------> +---------------+93 | |94 | |95 | | +---------------+96 | +----------------------> | Slave |97 | | Interface |98 | | 2 |99 | | |100 +----------------------------> | L + R |101 | (Data) |102 +---------------+103 104Example 5: Stereo Stream with L and R channel is rendered by two different105Ports of the Master and is received by only single Port of the Slave106interface. ::107 108 +--------------------+109 | |110 | +--------------+ +----------------+111 | | || | |112 | | Data Port || L Channel | |113 | | 1 |------------+ | |114 | | L Channel || | +-----+----+ |115 | | (Data) || | L + R Channel || Data | |116 | Master +----------+ | +---+---------> || Port | |117 | Interface | | || 1 | |118 | +--------------+ | || | |119 | | || | +----------+ |120 | | Data Port |------------+ | |121 | | 2 || R Channel | Slave |122 | | R Channel || | Interface |123 | | (Data) || | 1 |124 | +--------------+ Clock Signal | L + R |125 | +---------------------------> | (Data) |126 +--------------------+ | |127 +----------------+128 129Example 6: Stereo Stream with L and R channel is rendered by 2 Masters, each130rendering one channel, and is received by two different Slaves, each131receiving one channel. Both Masters and both Slaves are using single port. ::132 133 +---------------+ Clock Signal +---------------+134 | Master +----------------------------------+ Slave |135 | Interface | | Interface |136 | 1 | | 1 |137 | | Data Signal | |138 | L +----------------------------------+ L |139 | (Data) | Data Direction | (Data) |140 +---------------+ +-----------------------> +---------------+141 142 +---------------+ Clock Signal +---------------+143 | Master +----------------------------------+ Slave |144 | Interface | | Interface |145 | 2 | | 2 |146 | | Data Signal | |147 | R +----------------------------------+ R |148 | (Data) | Data Direction | (Data) |149 +---------------+ +-----------------------> +---------------+150 151Example 7: Stereo Stream with L and R channel is rendered by 2152Masters, each rendering both channels. Each Slave receives L + R. This153is the same application as Example 4 but with Slaves placed on154separate links. ::155 156 +---------------+ Clock Signal +---------------+157 | Master +----------------------------------+ Slave |158 | Interface | | Interface |159 | 1 | | 1 |160 | | Data Signal | |161 | L + R +----------------------------------+ L + R |162 | (Data) | Data Direction | (Data) |163 +---------------+ +-----------------------> +---------------+164 165 +---------------+ Clock Signal +---------------+166 | Master +----------------------------------+ Slave |167 | Interface | | Interface |168 | 2 | | 2 |169 | | Data Signal | |170 | L + R +----------------------------------+ L + R |171 | (Data) | Data Direction | (Data) |172 +---------------+ +-----------------------> +---------------+173 174Example 8: 4-channel Stream is rendered by 2 Masters, each rendering a1752 channels. Each Slave receives 2 channels. ::176 177 +---------------+ Clock Signal +---------------+178 | Master +----------------------------------+ Slave |179 | Interface | | Interface |180 | 1 | | 1 |181 | | Data Signal | |182 | L1 + R1 +----------------------------------+ L1 + R1 |183 | (Data) | Data Direction | (Data) |184 +---------------+ +-----------------------> +---------------+185 186 +---------------+ Clock Signal +---------------+187 | Master +----------------------------------+ Slave |188 | Interface | | Interface |189 | 2 | | 2 |190 | | Data Signal | |191 | L2 + R2 +----------------------------------+ L2 + R2 |192 | (Data) | Data Direction | (Data) |193 +---------------+ +-----------------------> +---------------+194 195Note1: In multi-link cases like above, to lock, one would acquire a global196lock and then go on locking bus instances. But, in this case the caller197framework(ASoC DPCM) guarantees that stream operations on a card are198always serialized. So, there is no race condition and hence no need for199global lock.200 201Note2: A Slave device may be configured to receive all channels202transmitted on a link for a given Stream (Example 4) or just a subset203of the data (Example 3). The configuration of the Slave device is not204handled by a SoundWire subsystem API, but instead by the205snd_soc_dai_set_tdm_slot() API. The platform or machine driver will206typically configure which of the slots are used. For Example 4, the207same slots would be used by all Devices, while for Example 3 the Slave208Device1 would use e.g. Slot 0 and Slave device2 slot 1.209 210Note3: Multiple Sink ports can extract the same information for the211same bitSlots in the SoundWire frame, however multiple Source ports212shall be configured with different bitSlot configurations. This is the213same limitation as with I2S/PCM TDM usages.214 215SoundWire Stream Management flow216================================217 218Stream definitions219------------------220 221 (1) Current stream: This is classified as the stream on which operation has222 to be performed like prepare, enable, disable, de-prepare etc.223 224 (2) Active stream: This is classified as the stream which is already active225 on Bus other than current stream. There can be multiple active streams226 on the Bus.227 228SoundWire Bus manages stream operations for each stream getting229rendered/captured on the SoundWire Bus. This section explains Bus operations230done for each of the stream allocated/released on Bus. Following are the231stream states maintained by the Bus for each of the audio stream.232 233 234SoundWire stream states235-----------------------236 237Below shows the SoundWire stream states and state transition diagram. ::238 239 +-----------+ +------------+ +----------+ +----------+240 | ALLOCATED +---->| CONFIGURED +---->| PREPARED +---->| ENABLED |241 | STATE | | STATE | | STATE | | STATE |242 +-----------+ +------------+ +---+--+---+ +----+-----+243 ^ ^ ^244 | | |245 __| |___________ |246 | | |247 v | v248 +----------+ +-----+------+ +-+--+-----+249 | RELEASED |<----------+ DEPREPARED |<-------+ DISABLED |250 | STATE | | STATE | | STATE |251 +----------+ +------------+ +----------+252 253NOTE: State transitions between ``SDW_STREAM_ENABLED`` and254``SDW_STREAM_DISABLED`` are only relevant when then INFO_PAUSE flag is255supported at the ALSA/ASoC level. Likewise the transition between256``SDW_DISABLED_STATE`` and ``SDW_PREPARED_STATE`` depends on the257INFO_RESUME flag.258 259NOTE2: The framework implements basic state transition checks, but260does not e.g. check if a transition from DISABLED to ENABLED is valid261on a specific platform. Such tests need to be added at the ALSA/ASoC262level.263 264Stream State Operations265-----------------------266 267Below section explains the operations done by the Bus on Master(s) and268Slave(s) as part of stream state transitions.269 270SDW_STREAM_ALLOCATED271~~~~~~~~~~~~~~~~~~~~272 273Allocation state for stream. This is the entry state274of the stream. Operations performed before entering in this state:275 276 (1) A stream runtime is allocated for the stream. This stream277 runtime is used as a reference for all the operations performed278 on the stream.279 280 (2) The resources required for holding stream runtime information are281 allocated and initialized. This holds all stream related information282 such as stream type (PCM/PDM) and parameters, Master and Slave283 interface associated with the stream, stream state etc.284 285After all above operations are successful, stream state is set to286``SDW_STREAM_ALLOCATED``.287 288Bus implements below API for allocate a stream which needs to be called once289per stream. From ASoC DPCM framework, this stream state maybe linked to290.startup() operation.291 292.. code-block:: c293 294 int sdw_alloc_stream(char * stream_name);295 296The SoundWire core provides a sdw_startup_stream() helper function,297typically called during a dailink .startup() callback, which performs298stream allocation and sets the stream pointer for all DAIs299connected to a stream.300 301SDW_STREAM_CONFIGURED302~~~~~~~~~~~~~~~~~~~~~303 304Configuration state of stream. Operations performed before entering in305this state:306 307 (1) The resources allocated for stream information in SDW_STREAM_ALLOCATED308 state are updated here. This includes stream parameters, Master(s)309 and Slave(s) runtime information associated with current stream.310 311 (2) All the Master(s) and Slave(s) associated with current stream provide312 the port information to Bus which includes port numbers allocated by313 Master(s) and Slave(s) for current stream and their channel mask.314 315After all above operations are successful, stream state is set to316``SDW_STREAM_CONFIGURED``.317 318Bus implements below APIs for CONFIG state which needs to be called by319the respective Master(s) and Slave(s) associated with stream. These APIs can320only be invoked once by respective Master(s) and Slave(s). From ASoC DPCM321framework, this stream state is linked to .hw_params() operation.322 323.. code-block:: c324 325 int sdw_stream_add_master(struct sdw_bus * bus,326 struct sdw_stream_config * stream_config,327 const struct sdw_ports_config * ports_config,328 struct sdw_stream_runtime * stream);329 330 int sdw_stream_add_slave(struct sdw_slave * slave,331 struct sdw_stream_config * stream_config,332 const struct sdw_ports_config * ports_config,333 struct sdw_stream_runtime * stream);334 335 336SDW_STREAM_PREPARED337~~~~~~~~~~~~~~~~~~~338 339Prepare state of stream. Operations performed before entering in this state:340 341 (0) Steps 1 and 2 are omitted in the case of a resume operation,342 where the bus bandwidth is known.343 344 (1) Bus parameters such as bandwidth, frame shape, clock frequency,345 are computed based on current stream as well as already active346 stream(s) on Bus. Re-computation is required to accommodate current347 stream on the Bus.348 349 (2) Transport and port parameters of all Master(s) and Slave(s) port(s) are350 computed for the current as well as already active stream based on frame351 shape and clock frequency computed in step 1.352 353 (3) Computed Bus and transport parameters are programmed in Master(s) and354 Slave(s) registers. The banked registers programming is done on the355 alternate bank (bank currently unused). Port(s) are enabled for the356 already active stream(s) on the alternate bank (bank currently unused).357 This is done in order to not disrupt already active stream(s).358 359 (4) Once all the values are programmed, Bus initiates switch to alternate360 bank where all new values programmed gets into effect.361 362 (5) Ports of Master(s) and Slave(s) for current stream are prepared by363 programming PrepareCtrl register.364 365After all above operations are successful, stream state is set to366``SDW_STREAM_PREPARED``.367 368Bus implements below API for PREPARE state which needs to be called369once per stream. From ASoC DPCM framework, this stream state is linked370to .prepare() operation. Since the .trigger() operations may not371follow the .prepare(), a direct transition from372``SDW_STREAM_PREPARED`` to ``SDW_STREAM_DEPREPARED`` is allowed.373 374.. code-block:: c375 376 int sdw_prepare_stream(struct sdw_stream_runtime * stream);377 378 379SDW_STREAM_ENABLED380~~~~~~~~~~~~~~~~~~381 382Enable state of stream. The data port(s) are enabled upon entering this state.383Operations performed before entering in this state:384 385 (1) All the values computed in SDW_STREAM_PREPARED state are programmed386 in alternate bank (bank currently unused). It includes programming of387 already active stream(s) as well.388 389 (2) All the Master(s) and Slave(s) port(s) for the current stream are390 enabled on alternate bank (bank currently unused) by programming391 ChannelEn register.392 393 (3) Once all the values are programmed, Bus initiates switch to alternate394 bank where all new values programmed gets into effect and port(s)395 associated with current stream are enabled.396 397After all above operations are successful, stream state is set to398``SDW_STREAM_ENABLED``.399 400Bus implements below API for ENABLE state which needs to be called once per401stream. From ASoC DPCM framework, this stream state is linked to402.trigger() start operation.403 404.. code-block:: c405 406 int sdw_enable_stream(struct sdw_stream_runtime * stream);407 408SDW_STREAM_DISABLED409~~~~~~~~~~~~~~~~~~~410 411Disable state of stream. The data port(s) are disabled upon exiting this state.412Operations performed before entering in this state:413 414 (1) All the Master(s) and Slave(s) port(s) for the current stream are415 disabled on alternate bank (bank currently unused) by programming416 ChannelEn register.417 418 (2) All the current configuration of Bus and active stream(s) are programmed419 into alternate bank (bank currently unused).420 421 (3) Once all the values are programmed, Bus initiates switch to alternate422 bank where all new values programmed gets into effect and port(s) associated423 with current stream are disabled.424 425After all above operations are successful, stream state is set to426``SDW_STREAM_DISABLED``.427 428Bus implements below API for DISABLED state which needs to be called once429per stream. From ASoC DPCM framework, this stream state is linked to430.trigger() stop operation.431 432When the INFO_PAUSE flag is supported, a direct transition to433``SDW_STREAM_ENABLED`` is allowed.434 435For resume operations where ASoC will use the .prepare() callback, the436stream can transition from ``SDW_STREAM_DISABLED`` to437``SDW_STREAM_PREPARED``, with all required settings restored but438without updating the bandwidth and bit allocation.439 440.. code-block:: c441 442 int sdw_disable_stream(struct sdw_stream_runtime * stream);443 444 445SDW_STREAM_DEPREPARED446~~~~~~~~~~~~~~~~~~~~~447 448De-prepare state of stream. Operations performed before entering in this449state:450 451 (1) All the port(s) of Master(s) and Slave(s) for current stream are452 de-prepared by programming PrepareCtrl register.453 454 (2) The payload bandwidth of current stream is reduced from the total455 bandwidth requirement of bus and new parameters calculated and456 applied by performing bank switch etc.457 458After all above operations are successful, stream state is set to459``SDW_STREAM_DEPREPARED``.460 461Bus implements below API for DEPREPARED state which needs to be called462once per stream. ALSA/ASoC do not have a concept of 'deprepare', and463the mapping from this stream state to ALSA/ASoC operation may be464implementation specific.465 466When the INFO_PAUSE flag is supported, the stream state is linked to467the .hw_free() operation - the stream is not deprepared on a468TRIGGER_STOP.469 470Other implementations may transition to the ``SDW_STREAM_DEPREPARED``471state on TRIGGER_STOP, should they require a transition through the472``SDW_STREAM_PREPARED`` state.473 474.. code-block:: c475 476 int sdw_deprepare_stream(struct sdw_stream_runtime * stream);477 478 479SDW_STREAM_RELEASED480~~~~~~~~~~~~~~~~~~~481 482Release state of stream. Operations performed before entering in this state:483 484 (1) Release port resources for all Master(s) and Slave(s) port(s)485 associated with current stream.486 487 (2) Release Master(s) and Slave(s) runtime resources associated with488 current stream.489 490 (3) Release stream runtime resources associated with current stream.491 492After all above operations are successful, stream state is set to493``SDW_STREAM_RELEASED``.494 495Bus implements below APIs for RELEASE state which needs to be called by496all the Master(s) and Slave(s) associated with stream. From ASoC DPCM497framework, this stream state is linked to .hw_free() operation.498 499.. code-block:: c500 501 int sdw_stream_remove_master(struct sdw_bus * bus,502 struct sdw_stream_runtime * stream);503 int sdw_stream_remove_slave(struct sdw_slave * slave,504 struct sdw_stream_runtime * stream);505 506 507The .shutdown() ASoC DPCM operation calls below Bus API to release508stream assigned as part of ALLOCATED state.509 510In .shutdown() the data structure maintaining stream state are freed up.511 512.. code-block:: c513 514 void sdw_release_stream(struct sdw_stream_runtime * stream);515 516The SoundWire core provides a sdw_shutdown_stream() helper function,517typically called during a dailink .shutdown() callback, which clears518the stream pointer for all DAIS connected to a stream and releases the519memory allocated for the stream.520 521Not Supported522=============523 5241. A single port with multiple channels supported cannot be used between two525 streams or across stream. For example a port with 4 channels cannot be used526 to handle 2 independent stereo streams even though it's possible in theory527 in SoundWire.528