linux-kernel - Re: [PATCH 2/4] dt-bindings: sound: add rockchip i2s-tdm binding

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Date:   Thu, 19 Aug 2021 15:16:17 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Nicolas Frattaroli <frattaroli.nicolas@...il.com>
Cc:     Liam Girdwood <lgirdwood@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Heiko Stuebner <heiko@...ech.de>,
        Robin Murphy <robin.murphy@....com>,
        alsa-devel@...a-project.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] dt-bindings: sound: add rockchip i2s-tdm binding

On Thu, Aug 19, 2021 at 03:52:55PM +0200, Nicolas Frattaroli wrote:
> On Donnerstag, 19. August 2021 14:08:36 CEST Robin Murphy wrote:

> > > +  rockchip,no-dmaengine:
> > > +    description:
> > > +      If present, driver will not register a pcm dmaengine, only the dai.
> > > +      If the dai is part of multi-dais, the property should be present.
> > > +    type: boolean

> > That sounds a lot more like a policy decision specific to the Linux
> > driver implementation, than something which really belongs in DT as a
> > description of the platform.

> I agree. Should I be refactoring this into a module parameter or
> something along those lines? I'm unsure of where this goes.

Why is this even required?  What is "multi-dais" and why would
registering the DMA stuff cause a problem?

> The particular configuration may even vary per-board; an I2S/TDM
> controller may be connected to an external codec which does not
> support capture, whereas on another board it may be connected to
> one that does.

If the external device doesn't support both directions then why does the
driver for the I2S controller in the CPU care?  The constraint handling
code in the core will ensure that nothing tries to start something that
isn't supported

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