linux-kernel - Re: [PATCH v2 1/3] ALSA: compress: document the compress audio state machine

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Date:   Mon, 22 Jun 2020 08:28:48 -0500
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Vinod Koul <vkoul@...nel.org>, Takashi Iwai <tiwai@...e.com>,
        Jaroslav Kysela <perex@...ex.cz>
Cc:     alsa-devel@...a-project.org,
        Charles Keepax <ckeepax@...nsource.cirrus.com>,
        linux-arm-msm@...r.kernel.org,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] ALSA: compress: document the compress audio state
 machine



On 6/22/20 1:58 AM, 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@...nel.org>
> ---
>   .../sound/designs/compress-offload.rst        | 52 +++++++++++++++++++
>   1 file changed, 52 insertions(+)
> 
> diff --git a/Documentation/sound/designs/compress-offload.rst b/Documentation/sound/designs/compress-offload.rst
> index ad4bfbdacc83..6f86db82298b 100644
> --- a/Documentation/sound/designs/compress-offload.rst
> +++ b/Documentation/sound/designs/compress-offload.rst
> @@ -151,6 +151,58 @@ 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()    +----------+                                  |
> +  |           |                              |                                        |
> +  |           |                              |                                        |
> +  |           |                              | compr_write()                          |
> +  |           |                              |                                        |
> +  |           |                              v                                        |
> +  |           |                         +----------+                                  |
> +  |           |                         |          |                                  |
> +  |           |                         |  PREPARE |                                  |
> +  |           |                         |          |                                  |
> +  |           |                         +----------+                                  |
> +  |           |                              |                                        |
> +  |           |                              |                                        |
> +  |           |                              | compr_start()                          |
> +  |           |                              |                                        |
> +  |           |                              v                                        |
> +  |     +----------+                    +----------+  compr_pause()  +----------+     |
> +  |     |          |    compr_drain()   |          |---------------->|          |     |
> +  |     |  DRAIN   |<-------------------|  RUNNING |                 |  PAUSE   |     |
> +  |     |          |                    |          |<----------------|          |     |
> +  |     +----------+                    +----------+  compr_resume() +----------+     |
> +  |           |                           |      |                                    |
> +  |           |                           |      |                                    |
> +  |           |                           |      |                                    |
> +  |           |                           |      |          compr_stop()              |
> +  |           |                           |      +------------------------------------+
> +  |           |       +----------+        |
> +  |           |       |          |        |
> +  +-----------+------>|          |<-------+
> +     compr_free()     |   FREE   |  compr_free()
> +                      |          |
> +                      +----------+
> +

Sorry, this confuses me even more...

a) can you clarify if we can go from running to free directly? is this 
really a legit transition? There's already the option of doing a stop 
and a a drain.

b) no way to go back to SETUP from PREPARE? What happens if the app 
never starts but want to tear down the resources?

c) no way to stop a paused stream?