linux-kernel - Re: [PATCH v15 00/16] Add audio support in v4l2 framework

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Message-ID: <28d423b1-49d8-4180-8394-622b1afd9cd9@perex.cz>
Date: Thu, 9 May 2024 13:13:34 +0200
From: Jaroslav Kysela <perex@...ex.cz>
To: Shengjiu Wang <shengjiu.wang@...il.com>,
 Amadeusz Sławiński
 <amadeuszx.slawinski@...ux.intel.com>
Cc: Hans Verkuil <hverkuil@...all.nl>,
 Mauro Carvalho Chehab <mchehab@...nel.org>, Mark Brown <broonie@...nel.org>,
 Takashi Iwai <tiwai@...e.de>,
 Sebastian Fricke <sebastian.fricke@...labora.com>,
 Shengjiu Wang <shengjiu.wang@....com>, sakari.ailus@....fi,
 tfiga@...omium.org, m.szyprowski@...sung.com, linux-media@...r.kernel.org,
 linux-kernel@...r.kernel.org, Xiubo.Lee@...il.com, festevam@...il.com,
 nicoleotsuka@...il.com, lgirdwood@...il.com, tiwai@...e.com,
 alsa-devel@...a-project.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v15 00/16] Add audio support in v4l2 framework

On 09. 05. 24 12:44, Shengjiu Wang wrote:
>>> mem2mem is just like the decoder in the compress pipeline. which is
>>> one of the components in the pipeline.
>>
>> I was thinking of loopback with endpoints using compress streams,
>> without physical endpoint, something like:
>>
>> compress playback (to feed data from userspace) -> DSP (processing) ->
>> compress capture (send data back to userspace)
>>
>> Unless I'm missing something, you should be able to process data as fast
>> as you can feed it and consume it in such case.
>>
> 
> Actually in the beginning I tried this,  but it did not work well.
> ALSA needs time control for playback and capture, playback and capture
> needs to synchronize.  Usually the playback and capture pipeline is
> independent in ALSA design,  but in this case, the playback and capture
> should synchronize, they are not independent.

The core compress API core no strict timing constraints. You can eventually0 
have two half-duplex compress devices, if you like to have really independent 
mechanism. If something is missing in API, you can extend this API (like to 
inform the user space that it's a producer/consumer processing without any 
relation to the real time). I like this idea.

					Jaroslav

-- 
Jaroslav Kysela <perex@...ex.cz>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.