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

[Pierre-Louis Bossart]

> +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   |
> +                                        +----------+

May I suggest having a single state machine, not a big one and an 
additional partial one. It would help explain why in one case 
compr_drain_notify() triggers a transition to RUNNING while in the other 
one it goes to SETUP.

I realize it's more complicated to edit but it'd be easier on 
reviewers/users.