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

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Message-ID: <b7120871-325c-4db0-a785-854b51ab680f@sirena.org.uk>
Date:   Wed, 2 Aug 2023 13:09:16 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Shengjiu Wang <shengjiu.wang@...il.com>
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 Wed, Aug 02, 2023 at 08:02:29PM +0800, Shengjiu Wang wrote:
> On Wed, Aug 2, 2023 at 7:22 PM Takashi Iwai <tiwai@...e.de> wrote:

> > Well, I personally don't mind to have some audio capability in v4l2
> > layer.  But, the only uncertain thing for now is whether this is a
> > must-have or not.

> Thanks,  I am also not sure about this.  I am also confused that why
> there is no m2m implementation for audio in the kernel.  Audio also
> has similar decoder encoder post-processing as video.

This is the thing where we've been trying to persuade people to work on
replacing DPCM with full componentisation for about a decade now but
nobody's had time other than Morimoto-san who's been chipping away at
making everything component based for a good chunk of that time.  One
trick is that we don't just want this to work for things that are memory
to memory, we also want things where there's a direct interconnect that
bypasses memory for off-SoC case.

> The reason why I select to extend v4l2 for such audio usage is that v4l2
> looks best for this audio m2m implementation.  v4l2 is designed for m2m
> usage.  if we need implement another 'route',  I don't think it can do better
> that v4l2.

> I appreciate that someone can share his ideas or doable solutions.
> And please don't ignore my request, ignore my patch.

There's a bunch of presentations Lars-Peter did at ELC some considerable
time ago about this.

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