linux-kernel - Re: [PATCH 0/4] ASoC: fsl_asrc: allow selecting arbitrary clocks

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Message-ID: <f05485be-b081-60a8-7fd0-f8020dc42375@collabora.com>
Date:   Thu, 16 Jul 2020 16:26:29 +0200
From:   Arnaud Ferraris <arnaud.ferraris@...labora.com>
To:     Mark Brown <broonie@...nel.org>,
        Nicolin Chen <nicoleotsuka@...il.com>
Cc:     alsa-devel@...a-project.org, Timur Tabi <timur@...nel.org>,
        Xiubo Li <Xiubo.Lee@...il.com>, linux-kernel@...r.kernel.org,
        Takashi Iwai <tiwai@...e.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Rob Herring <robh+dt@...nel.org>, kernel@...labora.com,
        Fabio Estevam <festevam@...il.com>
Subject: Re: [PATCH 0/4] ASoC: fsl_asrc: allow selecting arbitrary clocks



Le 16/07/2020 à 14:18, Mark Brown a écrit :
> On Wed, Jul 15, 2020 at 02:03:08PM -0700, Nicolin Chen wrote:
>> On Wed, Jul 15, 2020 at 03:05:19PM +0100, Mark Brown wrote:
>>> On Tue, Jul 14, 2020 at 01:50:50PM -0700, Nicolin Chen wrote:
> 
>>>> Thanks for the input. Fox i.MX6, I don't feel it would be that
>>>> drastically different though. And both SSI1 and SSI2 can simply
>>>> select the same root clock source to avoid that happen.
> 
>>> If you've got two radios that both need to sync to some radio derived
>>> frequency it gets a bit more entertaining.
> 
>> I'm simply curious what could be a problem. Do you mind educating
>> me a bit? And ASRC here isn't a radio but a sample rate converter
>> working as a BE in DPCM setup, using radio-capture for example...
> 
> My understanding was that this application was using the ASRC to convert
> between the sample rates of two different radios - the rates may be
> nominaly the same but in practice different so the audio will glitch
> after a while when the clocks drift far enough apart.

That's part of the issues we had to solve, yes. The other part is more
traditional sample rate conversion on an as-needed basis, as we can't
assume which rate will be used (iPhone's use 16kHz, Android phones stick
to 8kHz, and headsets can use both depending on their capabilities).