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

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Message-ID: <20200715140519.GH5431@sirena.org.uk>
Date:   Wed, 15 Jul 2020 15:05:19 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Nicolin Chen <nicoleotsuka@...il.com>
Cc:     Arnaud Ferraris <arnaud.ferraris@...labora.com>,
        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

On Tue, Jul 14, 2020 at 01:50:50PM -0700, Nicolin Chen wrote:
> On Tue, Jul 14, 2020 at 09:27:53PM +0100, Mark Brown wrote:

> > The nominal rate might be the same but if they're in different clock
> > domains then the actual rates might be different (hence the desire for
> > an ASRC I guess).  I can see the system wanting to choose one clock or
> > the other on the basis of some system specific property (quality of the
> > clock sources, tolerances of the devices involved or something) though
> > it's a rather fun edge case configuration :/ .

> 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.

> Yet, in case that we need to support such an edge case, what's
> a relatively common practice to allow system select the clock
> source now?

Honestly for anything that fun it tends to be a custom machine driver.
A property would seem reasonable though.

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