linux-kernel - Re: [RFC PATCH v2 0/7] Add audio support in v4l2 framework

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Message-ID: <CAA+D8AOnsx+7t3MrWm42waxtetL07nbKURLsh1hBx39LUDm+Zg@mail.gmail.com>
Date:   Thu, 3 Aug 2023 21:11:16 +0800
From:   Shengjiu Wang <shengjiu.wang@...il.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     Takashi Iwai <tiwai@...e.de>, Hans Verkuil <hverkuil@...all.nl>,
        Shengjiu Wang <shengjiu.wang@....com>, sakari.ailus@....fi,
        tfiga@...omium.org, m.szyprowski@...sung.com, mchehab@...nel.org,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        Xiubo.Lee@...il.com, festevam@...il.com, nicoleotsuka@...il.com,
        lgirdwood@...il.com, perex@...ex.cz, tiwai@...e.com,
        alsa-devel@...a-project.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [RFC PATCH v2 0/7] Add audio support in v4l2 framework

On Thu, Aug 3, 2023 at 1:28 AM Mark Brown <broonie@...nel.org> wrote:
>
> On Wed, Aug 02, 2023 at 10:41:43PM +0800, Shengjiu Wang wrote:
>
> > Currently the ASRC in ALSA is to connect to another I2S device as
> > a sound card.  But we'd like to the ASRC can be used by user space directly
> > that user space application can get the output after conversion from ASRC.
>
> That sort of use case would be handled via DPCM at the minute, though
> persuading it to connect two front ends together might be fun (which is
> the sort of reason why we want to push digital information down into
> DAPM and make everything a component).

Thanks.

ASRC M2M case needs to run as fast as possible, no sync clock control.
If use sound card to handle ASRC M2M case,  the user application
should be aplay/arecord, then we need to consider xrun issue, buffer
may timeout, sync between aplay and arecord,  these should't be
considered by pure memory to memory operation.

DPCM may achitect all the audio things in components and sound
card,  it is good. but for the M2M case, it is complcated. not sure
it is doable.

best regards
wang shengjiu