linux-kernel - Re: [RFC PATCH] ASoC: pcm_dmaengine: Add support for BE DAIs

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Message-ID: <b98d9b89-268b-5a4f-57bc-b7f95d6c81a4@microchip.com>
Date:   Fri, 11 Dec 2020 18:00:55 +0000
From:   <Codrin.Ciubotariu@...rochip.com>
To:     <broonie@...nel.org>
CC:     <alsa-devel@...a-project.org>, <linux-kernel@...r.kernel.org>,
        <lgirdwood@...il.com>, <tiwai@...e.com>, <perex@...ex.cz>,
        <lars@...afoo.de>
Subject: Re: [RFC PATCH] ASoC: pcm_dmaengine: Add support for BE DAIs

On 08.12.2020 21:31, Mark Brown wrote:
> On Tue, Dec 08, 2020 at 07:26:35PM +0000, Codrin.Ciubotariu@...rochip.com wrote:
> 
>> I do not know too much about the dummy PCM. It seems like it is creating
>> a card without DPCM links and fakes a buffer, which is not quite what I
>> need. I will investigate more.
> 
> Right, that's what I was imagining the second runtime you proposed
> looking like.
> 

I don't need the whole struct snd_pcm_runtime, only struct 
snd_pcm_hardware, at least for now. I looked some more and a suitable 
place would be struct snd_soc_dpcm, since it is created at runtime and 
used anyway to characterize a FE <-> BE link. What do you think?

Also, I noticed that the HW constraints added by a DAI driver (a codec 
for example) are added to PCM's runtime->hw_constraints, even if the DAI 
driver is part of a BE. Shouldn't these constraints be applied only to 
BE and eventually merge them to FE (struct snd_pcm_hardware) if 
dai_link->dpcm_merged_* are set?

Best regards,
Codrin