[PATCH v4 1/3] ALSA: compress: document the compress audio state machine

[Amadeusz Sławiński]

On 6/29/2020 9:50 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
> 
> Reviewed-by: Charles Keepax <ckeepax at opensource.cirrus.com>
> Signed-off-by: Vinod Koul <vkoul at 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()                  |
> +  |          |                              |                                |
> +  |          |                              |                                |
> +  |          |                         +----------+                          |
> +  |          |                         |          |   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
>   ================
> 

Line containing compr_free (between SETUP and FREE) seems to be misaligned?

If you move prepare to the left and drain in place of drain, it feels 
like you won't need this weird indirection with A
Something like:

 >> +                                             v
>> +         compr_free()                   +----------+
>> +  +------------------------------------|          |
>> +  |                                    |   SETUP  |
>> +  |          +------------------------>|          |<-------------------------+
>> +  |          | compr_write()           +----------+                          |
>> +  |          |                              ^                                |
>> +  |          |                              | compr_drain_notify() or        |
>> +  |          |                              | compr_stop()                   |
>> +  |          |                              |                                |
>> +  |          |                              |                                |
>> +  |          |                         +----------+                          |
>> +  |          |                         |          |                          |
>> +  |          |                         |  DRAIN   |                          |
>> +  |          |                         |          |                          |
>> +  |          |                         +----------+                          |
>> +  |          |                              ^                                |
>> +  |          |                              |                                |
>> +  |          |                              | compr_drain()                  |
>> +  |          |                              |                                |
>> +  |          |                              |                                |
>> +  |    +----------+                    +----------+                          |
>> +  |    |          |    compr_start()   |          |        compr_stop()      |
>> +  |    |  PREPARE |------------------->|  RUNNING |--------------------------+
>> +  |    |          |                    |          |                          |
>> +  |    +----------+                    +----------+                          |
>> +  |          |                            |    ^                             |
>> +  |          | compr_free()               |    |                             |
>> +  |          |              compr_pause() |    | compr_resume()              |
>> +  |          |                            |    |                             |
>> +  |          v                            v    |                             |
>> +  |    +----------+                   +----------+                           |
>> +  |    |          |                   |          |         compr_stop()      |
>> +  +--->|   FREE   |                   |  PAUSE   |---------------------------+
>> +       |          |                   |          |
>> +       +----------+                   +----------+
>> +

but this makes me question PREPARE state, how do you enter it?