| ========================= | |
| Audio Stream in SoundWire | |
| ========================= | |
| An audio stream is a logical or virtual connection created between | |
| (1) System memory buffer(s) and Codec(s) | |
| (2) DSP memory buffer(s) and Codec(s) | |
| (3) FIFO(s) and Codec(s) | |
| (4) Codec(s) and Codec(s) | |
| which is typically driven by a DMA(s) channel through the data link. An | |
| audio stream contains one or more channels of data. All channels within | |
| stream must have same sample rate and same sample size. | |
| Assume a stream with two channels (Left & Right) is opened using SoundWire | |
| interface. Below are some ways a stream can be represented in SoundWire. | |
| Stream Sample in memory (System memory, DSP memory or FIFOs) :: | |
| ------------------------- | |
| | L | R | L | R | L | R | | |
| ------------------------- | |
| Example 1: Stereo Stream with L and R channels is rendered from Master to | |
| Slave. Both Master and Slave is using single port. :: | |
| +---------------+ Clock Signal +---------------+ | |
| | Master +----------------------------------+ Slave | | |
| | Interface | | Interface | | |
| | | | 1 | | |
| | | Data Signal | | | |
| | L + R +----------------------------------+ L + R | | |
| | (Data) | Data Direction | (Data) | | |
| +---------------+ +-----------------------> +---------------+ | |
| Example 2: Stereo Stream with L and R channels is captured from Slave to | |
| Master. Both Master and Slave is using single port. :: | |
| +---------------+ Clock Signal +---------------+ | |
| | Master +----------------------------------+ Slave | | |
| | Interface | | Interface | | |
| | | | 1 | | |
| | | Data Signal | | | |
| | L + R +----------------------------------+ L + R | | |
| | (Data) | Data Direction | (Data) | | |
| +---------------+ <-----------------------+ +---------------+ | |
| Example 3: Stereo Stream with L and R channels is rendered by Master. Each | |
| of the L and R channel is received by two different Slaves. Master and both | |
| Slaves are using single port. :: | |
| +---------------+ Clock Signal +---------------+ | |
| | Master +---------+------------------------+ Slave | | |
| | Interface | | | Interface | | |
| | | | | 1 | | |
| | | | Data Signal | | | |
| | L + R +---+------------------------------+ L | | |
| | (Data) | | | Data Direction | (Data) | | |
| +---------------+ | | +-------------> +---------------+ | |
| | | | |
| | | | |
| | | +---------------+ | |
| | +----------------------> | Slave | | |
| | | Interface | | |
| | | 2 | | |
| | | | | |
| +----------------------------> | R | | |
| | (Data) | | |
| +---------------+ | |
| Example 4: Stereo Stream with L and R channel is rendered by two different | |
| Ports of the Master and is received by only single Port of the Slave | |
| interface. :: | |
| +--------------------+ | |
| | | | |
| | +--------------+ +----------------+ | |
| | | || | | | |
| | | Data Port || L Channel | | | |
| | | 1 |------------+ | | | |
| | | L Channel || | +-----+----+ | | |
| | | (Data) || | L + R Channel || Data | | | |
| | Master +----------+ | +---+---------> || Port | | | |
| | Interface | | || 1 | | | |
| | +--------------+ | || | | | |
| | | || | +----------+ | | |
| | | Data Port |------------+ | | | |
| | | 2 || R Channel | Slave | | |
| | | R Channel || | Interface | | |
| | | (Data) || | 1 | | |
| | +--------------+ Clock Signal | L + R | | |
| | +---------------------------> | (Data) | | |
| +--------------------+ | | | |
| +----------------+ | |
| SoundWire Stream Management flow | |
| ================================ | |
| Stream definitions | |
| ------------------ | |
| (1) Current stream: This is classified as the stream on which operation has | |
| to be performed like prepare, enable, disable, de-prepare etc. | |
| (2) Active stream: This is classified as the stream which is already active | |
| on Bus other than current stream. There can be multiple active streams | |
| on the Bus. | |
| SoundWire Bus manages stream operations for each stream getting | |
| rendered/captured on the SoundWire Bus. This section explains Bus operations | |
| done for each of the stream allocated/released on Bus. Following are the | |
| stream states maintained by the Bus for each of the audio stream. | |
| SoundWire stream states | |
| ----------------------- | |
| Below shows the SoundWire stream states and state transition diagram. :: | |
| +-----------+ +------------+ +----------+ +----------+ | |
| | ALLOCATED +---->| CONFIGURED +---->| PREPARED +---->| ENABLED | | |
| | STATE | | STATE | | STATE | | STATE | | |
| +-----------+ +------------+ +----------+ +----+-----+ | |
| ^ | |
| | | |
| | | |
| v | |
| +----------+ +------------+ +----+-----+ | |
| | RELEASED |<----------+ DEPREPARED |<-------+ DISABLED | | |
| | STATE | | STATE | | STATE | | |
| +----------+ +------------+ +----------+ | |
| NOTE: State transition between prepare and deprepare is supported in Spec | |
| but not in the software (subsystem) | |
| NOTE2: Stream state transition checks need to be handled by caller | |
| framework, for example ALSA/ASoC. No checks for stream transition exist in | |
| SoundWire subsystem. | |
| Stream State Operations | |
| ----------------------- | |
| Below section explains the operations done by the Bus on Master(s) and | |
| Slave(s) as part of stream state transitions. | |
| SDW_STREAM_ALLOCATED | |
| ~~~~~~~~~~~~~~~~~~~~ | |
| Allocation state for stream. This is the entry state | |
| of the stream. Operations performed before entering in this state: | |
| (1) A stream runtime is allocated for the stream. This stream | |
| runtime is used as a reference for all the operations performed | |
| on the stream. | |
| (2) The resources required for holding stream runtime information are | |
| allocated and initialized. This holds all stream related information | |
| such as stream type (PCM/PDM) and parameters, Master and Slave | |
| interface associated with the stream, stream state etc. | |
| After all above operations are successful, stream state is set to | |
| ``SDW_STREAM_ALLOCATED``. | |
| Bus implements below API for allocate a stream which needs to be called once | |
| per stream. From ASoC DPCM framework, this stream state maybe linked to | |
| .startup() operation. | |
| .. code-block:: c | |
| int sdw_alloc_stream(char * stream_name); | |
| SDW_STREAM_CONFIGURED | |
| ~~~~~~~~~~~~~~~~~~~~~ | |
| Configuration state of stream. Operations performed before entering in | |
| this state: | |
| (1) The resources allocated for stream information in SDW_STREAM_ALLOCATED | |
| state are updated here. This includes stream parameters, Master(s) | |
| and Slave(s) runtime information associated with current stream. | |
| (2) All the Master(s) and Slave(s) associated with current stream provide | |
| the port information to Bus which includes port numbers allocated by | |
| Master(s) and Slave(s) for current stream and their channel mask. | |
| After all above operations are successful, stream state is set to | |
| ``SDW_STREAM_CONFIGURED``. | |
| Bus implements below APIs for CONFIG state which needs to be called by | |
| the respective Master(s) and Slave(s) associated with stream. These APIs can | |
| only be invoked once by respective Master(s) and Slave(s). From ASoC DPCM | |
| framework, this stream state is linked to .hw_params() operation. | |
| .. code-block:: c | |
| int sdw_stream_add_master(struct sdw_bus * bus, | |
| struct sdw_stream_config * stream_config, | |
| struct sdw_ports_config * ports_config, | |
| struct sdw_stream_runtime * stream); | |
| int sdw_stream_add_slave(struct sdw_slave * slave, | |
| struct sdw_stream_config * stream_config, | |
| struct sdw_ports_config * ports_config, | |
| struct sdw_stream_runtime * stream); | |
| SDW_STREAM_PREPARED | |
| ~~~~~~~~~~~~~~~~~~~ | |
| Prepare state of stream. Operations performed before entering in this state: | |
| (1) Bus parameters such as bandwidth, frame shape, clock frequency, | |
| are computed based on current stream as well as already active | |
| stream(s) on Bus. Re-computation is required to accommodate current | |
| stream on the Bus. | |
| (2) Transport and port parameters of all Master(s) and Slave(s) port(s) are | |
| computed for the current as well as already active stream based on frame | |
| shape and clock frequency computed in step 1. | |
| (3) Computed Bus and transport parameters are programmed in Master(s) and | |
| Slave(s) registers. The banked registers programming is done on the | |
| alternate bank (bank currently unused). Port(s) are enabled for the | |
| already active stream(s) on the alternate bank (bank currently unused). | |
| This is done in order to not disrupt already active stream(s). | |
| (4) Once all the values are programmed, Bus initiates switch to alternate | |
| bank where all new values programmed gets into effect. | |
| (5) Ports of Master(s) and Slave(s) for current stream are prepared by | |
| programming PrepareCtrl register. | |
| After all above operations are successful, stream state is set to | |
| ``SDW_STREAM_PREPARED``. | |
| Bus implements below API for PREPARE state which needs to be called once per | |
| stream. From ASoC DPCM framework, this stream state is linked to | |
| .prepare() operation. | |
| .. code-block:: c | |
| int sdw_prepare_stream(struct sdw_stream_runtime * stream); | |
| SDW_STREAM_ENABLED | |
| ~~~~~~~~~~~~~~~~~~ | |
| Enable state of stream. The data port(s) are enabled upon entering this state. | |
| Operations performed before entering in this state: | |
| (1) All the values computed in SDW_STREAM_PREPARED state are programmed | |
| in alternate bank (bank currently unused). It includes programming of | |
| already active stream(s) as well. | |
| (2) All the Master(s) and Slave(s) port(s) for the current stream are | |
| enabled on alternate bank (bank currently unused) by programming | |
| ChannelEn register. | |
| (3) Once all the values are programmed, Bus initiates switch to alternate | |
| bank where all new values programmed gets into effect and port(s) | |
| associated with current stream are enabled. | |
| After all above operations are successful, stream state is set to | |
| ``SDW_STREAM_ENABLED``. | |
| Bus implements below API for ENABLE state which needs to be called once per | |
| stream. From ASoC DPCM framework, this stream state is linked to | |
| .trigger() start operation. | |
| .. code-block:: c | |
| int sdw_enable_stream(struct sdw_stream_runtime * stream); | |
| SDW_STREAM_DISABLED | |
| ~~~~~~~~~~~~~~~~~~~ | |
| Disable state of stream. The data port(s) are disabled upon exiting this state. | |
| Operations performed before entering in this state: | |
| (1) All the Master(s) and Slave(s) port(s) for the current stream are | |
| disabled on alternate bank (bank currently unused) by programming | |
| ChannelEn register. | |
| (2) All the current configuration of Bus and active stream(s) are programmed | |
| into alternate bank (bank currently unused). | |
| (3) Once all the values are programmed, Bus initiates switch to alternate | |
| bank where all new values programmed gets into effect and port(s) associated | |
| with current stream are disabled. | |
| After all above operations are successful, stream state is set to | |
| ``SDW_STREAM_DISABLED``. | |
| Bus implements below API for DISABLED state which needs to be called once | |
| per stream. From ASoC DPCM framework, this stream state is linked to | |
| .trigger() stop operation. | |
| .. code-block:: c | |
| int sdw_disable_stream(struct sdw_stream_runtime * stream); | |
| SDW_STREAM_DEPREPARED | |
| ~~~~~~~~~~~~~~~~~~~~~ | |
| De-prepare state of stream. Operations performed before entering in this | |
| state: | |
| (1) All the port(s) of Master(s) and Slave(s) for current stream are | |
| de-prepared by programming PrepareCtrl register. | |
| (2) The payload bandwidth of current stream is reduced from the total | |
| bandwidth requirement of bus and new parameters calculated and | |
| applied by performing bank switch etc. | |
| After all above operations are successful, stream state is set to | |
| ``SDW_STREAM_DEPREPARED``. | |
| Bus implements below API for DEPREPARED state which needs to be called once | |
| per stream. From ASoC DPCM framework, this stream state is linked to | |
| .trigger() stop operation. | |
| .. code-block:: c | |
| int sdw_deprepare_stream(struct sdw_stream_runtime * stream); | |
| SDW_STREAM_RELEASED | |
| ~~~~~~~~~~~~~~~~~~~ | |
| Release state of stream. Operations performed before entering in this state: | |
| (1) Release port resources for all Master(s) and Slave(s) port(s) | |
| associated with current stream. | |
| (2) Release Master(s) and Slave(s) runtime resources associated with | |
| current stream. | |
| (3) Release stream runtime resources associated with current stream. | |
| After all above operations are successful, stream state is set to | |
| ``SDW_STREAM_RELEASED``. | |
| Bus implements below APIs for RELEASE state which needs to be called by | |
| all the Master(s) and Slave(s) associated with stream. From ASoC DPCM | |
| framework, this stream state is linked to .hw_free() operation. | |
| .. code-block:: c | |
| int sdw_stream_remove_master(struct sdw_bus * bus, | |
| struct sdw_stream_runtime * stream); | |
| int sdw_stream_remove_slave(struct sdw_slave * slave, | |
| struct sdw_stream_runtime * stream); | |
| The .shutdown() ASoC DPCM operation calls below Bus API to release | |
| stream assigned as part of ALLOCATED state. | |
| In .shutdown() the data structure maintaining stream state are freed up. | |
| .. code-block:: c | |
| void sdw_release_stream(struct sdw_stream_runtime * stream); | |
| Not Supported | |
| ============= | |
| 1. A single port with multiple channels supported cannot be used between two | |
| streams or across stream. For example a port with 4 channels cannot be used | |
| to handle 2 independent stereo streams even though it's possible in theory | |
| in SoundWire. |