soundwire: stream: update state machine and add state checks

The state machine and notes don't accurately explain or allow
transitions from STREAM_DEPREPARED and STREAM_DISABLED.

Add more explanations and allow for more transitions as a result of a
trigger_stop(), trigger_suspend() and prepare(), depending on the
ALSA/ASoC layer behavior defined by the INFO_RESUME and INFO_PAUSE
flags.

Also add basic checks to help debug inconsistent states and illegal
state machine transitions.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200114235227.14502-2-pierre-louis.bossart@linux.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

1 files changed, 44 insertions, 17 deletions

diff --git a/Documentation/driver-api/soundwire/stream.rst b/Documentation/driver-api/soundwire/stream.rst
index 5351bd2f34a8..8bceece51554 100644
--- a/Documentation/driver-api/soundwire/stream.rst
+++ b/Documentation/driver-api/soundwire/stream.rst
@@ -156,22 +156,27 @@ Below shows the SoundWire stream states and state transition diagram. ::
 	+-----------+     +------------+     +----------+     +----------+
 	| ALLOCATED +---->| CONFIGURED +---->| PREPARED +---->| ENABLED  |
 	|   STATE   |     |    STATE   |     |  STATE   |     |  STATE   |
-	+-----------+     +------------+     +----------+     +----+-----+
-	                                                           ^
-	                                                           |
-	                                                           |
-	                                                           v
-	         +----------+           +------------+        +----+-----+
+	+-----------+     +------------+     +---+--+---+     +----+-----+
+	                                         ^  ^              ^
+				                 |  |              |
+				               __|  |___________   |
+				              |                 |  |
+	                                      v                 |  v
+	         +----------+           +-----+------+        +-+--+-----+
 	         | RELEASED |<----------+ DEPREPARED |<-------+ DISABLED |
 	         |  STATE   |           |   STATE    |        |  STATE   |
 	         +----------+           +------------+        +----------+
 
-NOTE: State transition between prepare and deprepare is supported in Spec
-but not in the software (subsystem)
+NOTE: State transitions between ``SDW_STREAM_ENABLED`` and
+``SDW_STREAM_DISABLED`` are only relevant when then INFO_PAUSE flag is
+supported at the ALSA/ASoC level. Likewise the transition between
+``SDW_DISABLED_STATE`` and ``SDW_PREPARED_STATE`` depends on the
+INFO_RESUME flag.
 
-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.
+NOTE2: The framework implements basic state transition checks, but
+does not e.g. check if a transition from DISABLED to ENABLED is valid
+on a specific platform. Such tests need to be added at the ALSA/ASoC
+level.
 
 Stream State Operations
 -----------------------
@@ -246,6 +251,9 @@ SDW_STREAM_PREPARED
 
 Prepare state of stream. Operations performed before entering in this state:
 
+  (0) Steps 1 and 2 are omitted in the case of a resume operation,
+      where the bus bandwidth is known.
+
   (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
@@ -270,9 +278,11 @@ Prepare state of stream. Operations performed before entering in this state:
 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.
+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. Since the .trigger() operations may not
+follow the .prepare(), a direct transition from
+``SDW_STREAM_PREPARED`` to ``SDW_STREAM_DEPREPARED`` is allowed.
 
 .. code-block:: c
 
@@ -332,6 +342,14 @@ 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.
 
+When the INFO_PAUSE flag is supported, a direct transition to
+``SDW_STREAM_ENABLED`` is allowed.
+
+For resume operations where ASoC will use the .prepare() callback, the
+stream can transition from ``SDW_STREAM_DISABLED`` to
+``SDW_STREAM_PREPARED``, with all required settings restored but
+without updating the bandwidth and bit allocation.
+
 .. code-block:: c
 
   int sdw_disable_stream(struct sdw_stream_runtime * stream);
@@ -353,9 +371,18 @@ state:
 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.
+Bus implements below API for DEPREPARED state which needs to be called
+once per stream. ALSA/ASoC do not have a concept of 'deprepare', and
+the mapping from this stream state to ALSA/ASoC operation may be
+implementation specific.
+
+When the INFO_PAUSE flag is supported, the stream state is linked to
+the .hw_free() operation - the stream is not deprepared on a
+TRIGGER_STOP.
+
+Other implementations may transition to the ``SDW_STREAM_DEPREPARED``
+state on TRIGGER_STOP, should they require a transition through the
+``SDW_STREAM_PREPARED`` state.
 
 .. code-block:: c