[alsa-devel] Back-end state transition query

[Patrick Lai]

Hi Liam,

I am facing an issue related to how DPCM manages state of back-end
substream. Here is description of problem:

When front-end PCM substream is in paused state, back-end PCM substream
will be put in paused state as well if given front-end PCM substream is
the only client of given back-end. Based on current implementation of
DPCM, when application closes front-end PCM substream, DPCM framework
will not allow back-end enter HW_FREE state so back-end will never get
shutdown completely as well.

refer to function soc_dpcm_be_dai_hw_free(), here is the check for states

     if ((be->dpcm[stream].state != SND_SOC_DPCM_STATE_HW_PARAMS) &&
         (be->dpcm[stream].state != SND_SOC_DPCM_STATE_PREPARE) &&
         (be->dpcm[stream].state != SND_SOC_DPCM_STATE_HW_FREE) &&
         (be->dpcm[stream].state != SND_SOC_DPCM_STATE_STOP))
                         continue;

Can't DPCM also allow back-end hardware being freed in STATE_PAUSED?
Even if DPCM expects trigger stop coming to update back-end state to 
STATE_STOP, the following condition check will never allow back-end 
enter stop state anyway

Refer to soc_dpcm_be_dai_trigger()

   case SNDRV_PCM_TRIGGER_STOP:
      if (be->dpcm[stream].state != SND_SOC_DPCM_STATE_START)
                                 continue;

Can you please take a look and recommend the appropriate state 
transition or it would be okay to allow PAUSED state in 
soc_dpcm_be_dai_hw_free()?

Thanks
Patrick

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