[Sound-open-firmware] the SOF state machine issue

[zhigangw]

Hello All:

         I analysis the state machine of the SOF, and find something 
incorrect.

I attached the diagram in this email.

In this diagram, I only draw the correct flow, the incorrect part I did 
not draw it, if not,

It will cause this picture too complicated.


there are four states: ACTIVITY, PREPARE, READY, PAUSED in this state 
machine.

between each state, there are several arrows, which represents the command.

Notes: the red arrow and word is added by myself.


The problem is:

1. When the component stays at "PREPARE", if the "PAUSE" command comes, 
it will return error.

When the XRUN happens, the recover process will set the component in 
this pipeline in "PREPARE" state,

At this time, the "PAUSE" command comes, which will cause this issue.

2. When the component stays at "PREPARE", the "RELEASE" command would 
also comes.


Solution:

1. This is the first proposal:

I add the red arrow and word to display my solution.

When the "PAUSE" command comes, the state transfers from "PREPARE" to 
"PAUSED".

When the "RELEASE" command comes, the state transfers from "PREPARE" to 
"ACTIVITY".


2. This is the second proposal:

Make the "pipeline_xrun_recover()" function atomic, which might avoid 
this kind of issue.

But which would have long latency.


Thanks

~Zhigang