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