[alsa-devel] Question about DPCM FE vs BE

[Pierre-Louis Bossart]

On 10/9/19 2:57 AM, Kuninori Morimoto wrote:
> 
> Hi ALSA ML
> 
> In my understanding, DPCM needs FE and BE.
> And, one FE can have multiple BE, and one BE can have multiple FE.
> 
> My question this time is that one snd_soc_pcm_runtime can be both
> FE and BE in the same time (= Sometimes FE, sometimes BE) ??
> 
> In my understanding, it never happen.
> But, is this correct ?

It is my understanding that the current code would not support a case 
where a FE is also a BE.

That said, do we want to preclude it? at some point we probably want to 
get rid of the FE/BE distinction and have 'domains' that can be chained. 
So it may not be a good thing to cast a restriction in stone. If at some 
point we need a list of upstream/downstream clients maybe we should keep 
this.

> 
> I'm asking because do we need .be_clients/.fe_clients ?
> If one pcm_runtime can't be FE / BE in the same time,
> just .clients is enough I think.
> 
> 	static int dpcm_be_connect(...)
> 	{
> 		...
> -		list_add(&dpcm->list_be, &fe->dpcm[stream].be_clients);
> -		list_add(&dpcm->list_fe, &be->dpcm[stream].fe_clients);
> +		list_add(&dpcm->list_be, &fe->dpcm[stream].clients);
> +		list_add(&dpcm->list_fe, &be->dpcm[stream].clients);
> 		...
> 	}
> 
> 
> Thank you for your help !!
> Best regards
> ---
> Kuninori Morimoto
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