[alsa-devel] Back-end state transition query

Liam Girdwood lrg at ti.com
Thu Oct 25 19:59:16 CEST 2012

Hi Patrick,

On 25/10/12 08:40, Patrick Lai wrote:
> 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?

This seems like a bug. We should hw_free() the BE here.

> 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()
>      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()?

It should be OK to allow the paused state in hw_free(), but I'm thinking we should probably see the trigger stop when we close the FE (although I'm not 100% certain atm of seeing the STOP as I've not traced this PAUSE -> CLOSE sequence). I assume you have a patch that allows this ?



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