| ========================= |
| 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) | |
| +--------------------+ | | |
| +----------------+ |
| |
| Example 5: Stereo Stream with L and R channel is rendered by 2 Masters, each |
| rendering one channel, and is received by two different Slaves, each |
| receiving one channel. Both Masters and both Slaves are using single port. :: |
| |
| +---------------+ Clock Signal +---------------+ |
| | Master +----------------------------------+ Slave | |
| | Interface | | Interface | |
| | 1 | | 1 | |
| | | Data Signal | | |
| | L +----------------------------------+ L | |
| | (Data) | Data Direction | (Data) | |
| +---------------+ +-----------------------> +---------------+ |
| |
| +---------------+ Clock Signal +---------------+ |
| | Master +----------------------------------+ Slave | |
| | Interface | | Interface | |
| | 2 | | 2 | |
| | | Data Signal | | |
| | R +----------------------------------+ R | |
| | (Data) | Data Direction | (Data) | |
| +---------------+ +-----------------------> +---------------+ |
| |
| Note: In multi-link cases like above, to lock, one would acquire a global |
| lock and then go on locking bus instances. But, in this case the caller |
| framework(ASoC DPCM) guarantees that stream operations on a card are |
| always serialized. So, there is no race condition and hence no need for |
| global lock. |
| |
| 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. |
