[PATCH v3 0/3] ALSA: compress: Document stream states and fix gapless SM

[PATCH v3 0/3] ALSA: compress: Document stream states and fix gapless SM

[Vinod Koul]

Srini found issue with gapless implementation which prompted to look deeper
into SM for compressed stream.

So documenting SM was first step, so first two patches add that. Last patch
fixes the issue by keeping track on partial_drain and then moving state to
'running' in snd_compr_drain_notify() for partial_drain case on success.
While at it, noticed snd_compr_drain_notify() is lockless state change, so
fixed that as well.

I have tested this on Dragon board RB3, compressed audio works out of the
box on that platform and Srini will send driver and fcplay patches for
gapless soon.

Changes in v3:
 - Add pause->stop->free transition
 - Add setup->free transition
 - remove running->free as that goes thru stop

Changes in v2:
 - Added tested tag by Srini
 - Update compress SM with Free state and compr_stop() transitions

Vinod Koul (3):
  ALSA: compress: document the compress audio state machine
  ALSA: compress: document the compress gapless audio state machine
  ALSA: compress: fix partial_drain completion state

 .../sound/designs/compress-offload.rst        | 83 +++++++++++++++++++
 include/sound/compress_driver.h               | 12 ++-
 sound/core/compress_offload.c                 |  4 +
 3 files changed, 98 insertions(+), 1 deletion(-)

-- 
2.26.2

[PATCH v3 1/3] ALSA: compress: document the compress audio state machine

[Vinod Koul]

So we had some discussions of the stream states, so I thought it is a
good idea to document the state transitions, so add it documentation

Signed-off-by: Vinod Koul <vkoul@kernel.org>
---
 .../sound/designs/compress-offload.rst        | 51 +++++++++++++++++++
 1 file changed, 51 insertions(+)

diff --git a/Documentation/sound/designs/compress-offload.rst b/Documentation/sound/designs/compress-offload.rst
index ad4bfbdacc83..b6e9025ae105 100644
--- a/Documentation/sound/designs/compress-offload.rst
+++ b/Documentation/sound/designs/compress-offload.rst
@@ -151,6 +151,57 @@ Modifications include:
 - Addition of encoding options when required (derived from OpenMAX IL)
 - Addition of rateControlSupported (missing in OpenMAX AL)
 
+State Machine
+=============
+
+The compressed audio stream state machine is described below ::
+
+                                        +----------+
+                                        |          |
+                                        |   OPEN   |
+                                        |          |
+                                        +----------+
+                                             |
+                                             |
+                                             | compr_set_params()
+                                             |
+                                             v
+         compr_free()                   +----------+
+  +------------------------------------|          |
+  |                                    |   SETUP  |
+  |          +------------------------>|          |<-------------------------+
+  |          | compr_drain_notify()    +----------+                          |
+  |          |         or                   |                                |
+  |          |      compr_stop()            |                                |
+  |          |                              | compr_write()                  |
+  |          |                              |                                |
+  |          |                              v                                |
+  |          |                         +----------+                          |
+  |          |                         |          |   compr_free()           |
+  |          |                         |  PREPARE |---------------> A        |
+  |          |                         |          |                          |
+  |          |                         +----------+                          |
+  |          |                              |                                |
+  |          |                              |                                |
+  |          |                              | compr_start()                  |
+  |          |                              |                                |
+  |          |                              v                                |
+  |    +----------+                    +----------+                          |
+  |    |          |    compr_drain()   |          |        compr_stop()      |
+  |    |  DRAIN   |<-------------------|  RUNNING |--------------------------+
+  |    |          |                    |          |                          |
+  |    +----------+                    +----------+                          |
+  |                                       |    ^                             |
+  |          A                            |    |                             |
+  |          |              compr_pause() |    | compr_resume()              |
+  |          |                            |    |                             |
+  |          v                            v    |                             |
+  |    +----------+                   +----------+                           |
+  |    |          |                   |          |         compr_stop()      |
+  +--->|   FREE   |                   |  PAUSE   |---------------------------+
+       |          |                   |          |
+       +----------+                   +----------+
+
 
 Gapless Playback
 ================
-- 
2.26.2

[PATCH v3 2/3] ALSA: compress: document the compress gapless audio state machine

[Vinod Koul]

Also documented the galpess transitions. Please note that these are not
really stream states, but show how the stream steps in gapless mode

Signed-off-by: Vinod Koul <vkoul@kernel.org>
---
 .../sound/designs/compress-offload.rst        | 32 +++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/Documentation/sound/designs/compress-offload.rst b/Documentation/sound/designs/compress-offload.rst
index b6e9025ae105..82950dbbc4a9 100644
--- a/Documentation/sound/designs/compress-offload.rst
+++ b/Documentation/sound/designs/compress-offload.rst
@@ -250,6 +250,38 @@ Sequence flow for gapless would be:
 
 (note: order for partial_drain and write for next track can be reversed as well)
 
+Gapless Playback SM
+===================
+
+For Gapless, we move from running state to partial drain and back, along
+with setting of meta_data and signalling for next track ::
+
+
+                                        +----------+
+                compr_drain_notify()    |          |
+              +------------------------>|  RUNNING |
+              |                         |          |
+              |                         +----------+
+              |                              |
+              |                              |
+              |                              | compr_next_track()
+              |                              |
+              |                              v
+              |                         +----------+
+              |                         |          |
+              |                         |NEXT_TRACK|
+              |                         |          |
+              |                         +----------+
+              |                              |
+              |                              |
+              |                              | compr_partial_drain()
+              |                              |
+              |                              v
+              |                         +----------+
+              |                         |          |
+              +------------------------ | PARTIAL_ |
+                                        |  DRAIN   |
+                                        +----------+
 
 Not supported
 =============
-- 
2.26.2

[PATCH v3 3/3] ALSA: compress: fix partial_drain completion state

[Vinod Koul]

On partial_drain completion we should be in SNDRV_PCM_STATE_RUNNING
state, so set that for partially draining streams in
snd_compr_drain_notify() and use a flag for partially draining streams

While at it, add locks for stream state change in
snd_compr_drain_notify() as well.

Fixes: f44f2a5417b2 ("ALSA: compress: fix drain calls blocking other compress functions (v6)")
Reviewed-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Tested-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Vinod Koul <vkoul@kernel.org>
---
 include/sound/compress_driver.h | 12 +++++++++++-
 sound/core/compress_offload.c   |  4 ++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/include/sound/compress_driver.h b/include/sound/compress_driver.h
index 3df8d8c90191..93a5897201ea 100644
--- a/include/sound/compress_driver.h
+++ b/include/sound/compress_driver.h
@@ -66,6 +66,7 @@ struct snd_compr_runtime {
  * @direction: stream direction, playback/recording
  * @metadata_set: metadata set flag, true when set
  * @next_track: has userspace signal next track transition, true when set
+ * @partial_drain: undergoing partial_drain for stream, true when set
  * @private_data: pointer to DSP private data
  * @dma_buffer: allocated buffer if any
  */
@@ -78,6 +79,7 @@ struct snd_compr_stream {
 	enum snd_compr_direction direction;
 	bool metadata_set;
 	bool next_track;
+	bool partial_drain;
 	void *private_data;
 	struct snd_dma_buffer dma_buffer;
 };
@@ -187,7 +189,15 @@ static inline void snd_compr_drain_notify(struct snd_compr_stream *stream)
 	if (snd_BUG_ON(!stream))
 		return;
 
-	stream->runtime->state = SNDRV_PCM_STATE_SETUP;
+	mutex_lock(&stream->device->lock);
+	/* for partial_drain case we are back to running state on success */
+	if (stream->partial_drain) {
+		stream->runtime->state = SNDRV_PCM_STATE_RUNNING;
+		stream->partial_drain = false; /* clear this flag as well */
+	} else {
+		stream->runtime->state = SNDRV_PCM_STATE_SETUP;
+	}
+	mutex_unlock(&stream->device->lock);
 
 	wake_up(&stream->runtime->sleep);
 }
diff --git a/sound/core/compress_offload.c b/sound/core/compress_offload.c
index e618580feac4..1c4b2cf450a0 100644
--- a/sound/core/compress_offload.c
+++ b/sound/core/compress_offload.c
@@ -803,6 +803,9 @@ static int snd_compr_stop(struct snd_compr_stream *stream)
 
 	retval = stream->ops->trigger(stream, SNDRV_PCM_TRIGGER_STOP);
 	if (!retval) {
+		/* clear flags and stop any drain wait */
+		stream->partial_drain = false;
+		stream->metadata_set = false;
 		snd_compr_drain_notify(stream);
 		stream->runtime->total_bytes_available = 0;
 		stream->runtime->total_bytes_transferred = 0;
@@ -960,6 +963,7 @@ static int snd_compr_partial_drain(struct snd_compr_stream *stream)
 	if (stream->next_track == false)
 		return -EPERM;
 
+	stream->partial_drain = true;
 	retval = stream->ops->trigger(stream, SND_COMPR_TRIGGER_PARTIAL_DRAIN);
 	if (retval) {
 		pr_debug("Partial drain returned failure\n");
-- 
2.26.2

Re: [PATCH v3 3/3] ALSA: compress: fix partial_drain completion state

[Charles Keepax]

On Thu, Jun 25, 2020 at 09:16:51PM +0530, Vinod Koul wrote:
> On partial_drain completion we should be in SNDRV_PCM_STATE_RUNNING
> state, so set that for partially draining streams in
> snd_compr_drain_notify() and use a flag for partially draining streams
> 
> While at it, add locks for stream state change in
> snd_compr_drain_notify() as well.
> 
> Fixes: f44f2a5417b2 ("ALSA: compress: fix drain calls blocking other compress functions (v6)")
> Reviewed-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
> Tested-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
> Signed-off-by: Vinod Koul <vkoul@kernel.org>
> ---
> @@ -187,7 +189,15 @@ static inline void snd_compr_drain_notify(struct snd_compr_stream *stream)
>  	if (snd_BUG_ON(!stream))
>  		return;
>  
> -	stream->runtime->state = SNDRV_PCM_STATE_SETUP;
> +	mutex_lock(&stream->device->lock);
> +	/* for partial_drain case we are back to running state on success */
> +	if (stream->partial_drain) {
> +		stream->runtime->state = SNDRV_PCM_STATE_RUNNING;
> +		stream->partial_drain = false; /* clear this flag as well */
> +	} else {
> +		stream->runtime->state = SNDRV_PCM_STATE_SETUP;
> +	}
> +	mutex_unlock(&stream->device->lock);

You have added locking here in snd_compr_drain_notify but....
>  
>  	wake_up(&stream->runtime->sleep);
>  }
> diff --git a/sound/core/compress_offload.c b/sound/core/compress_offload.c
> index e618580feac4..1c4b2cf450a0 100644
> --- a/sound/core/compress_offload.c
> +++ b/sound/core/compress_offload.c
> @@ -803,6 +803,9 @@ static int snd_compr_stop(struct snd_compr_stream *stream)
>  
>  	retval = stream->ops->trigger(stream, SNDRV_PCM_TRIGGER_STOP);
>  	if (!retval) {
> +		/* clear flags and stop any drain wait */
> +		stream->partial_drain = false;
> +		stream->metadata_set = false;
>  		snd_compr_drain_notify(stream);

that can be called from snd_compr_stop here which is already
holding the lock resulting in deadlock.

Thanks,
Charles

Re: [PATCH v3 1/3] ALSA: compress: document the compress audio state machine

[Charles Keepax]

On Thu, Jun 25, 2020 at 09:16:49PM +0530, Vinod Koul wrote:
> So we had some discussions of the stream states, so I thought it is a
> good idea to document the state transitions, so add it documentation
> 
> Signed-off-by: Vinod Koul <vkoul@kernel.org>
> ---

Reviewed-by: Charles Keepax <ckeepax@opensource.cirrus.com>

Thanks,
Charles

Re: [PATCH v3 3/3] ALSA: compress: fix partial_drain completion state

[Vinod Koul]

On 26-06-20, 10:35, Charles Keepax wrote:

> > -	stream->runtime->state = SNDRV_PCM_STATE_SETUP;
> > +	mutex_lock(&stream->device->lock);
> > +	/* for partial_drain case we are back to running state on success */
> > +	if (stream->partial_drain) {
> > +		stream->runtime->state = SNDRV_PCM_STATE_RUNNING;
> > +		stream->partial_drain = false; /* clear this flag as well */
> > +	} else {
> > +		stream->runtime->state = SNDRV_PCM_STATE_SETUP;
> > +	}
> > +	mutex_unlock(&stream->device->lock);
> 
> You have added locking here in snd_compr_drain_notify but....
> >  
> >  	wake_up(&stream->runtime->sleep);
> >  }
> > diff --git a/sound/core/compress_offload.c b/sound/core/compress_offload.c
> > index e618580feac4..1c4b2cf450a0 100644
> > --- a/sound/core/compress_offload.c
> > +++ b/sound/core/compress_offload.c
> > @@ -803,6 +803,9 @@ static int snd_compr_stop(struct snd_compr_stream *stream)
> >  
> >  	retval = stream->ops->trigger(stream, SNDRV_PCM_TRIGGER_STOP);
> >  	if (!retval) {
> > +		/* clear flags and stop any drain wait */
> > +		stream->partial_drain = false;
> > +		stream->metadata_set = false;
> >  		snd_compr_drain_notify(stream);
> 
> that can be called from snd_compr_stop here which is already
> holding the lock resulting in deadlock.

Thanks Charles, right somehow my testing missed this, have verified that
it is the case.

I will remove the locks here, and we should add a comment to note this..

Thanks

-- 
~Vinod