linux-kernel - Re: [PATCH v1 2/2] dt-bindings: ASoC: simple-card: Add system-clock-id property

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Date:   Tue, 25 Oct 2022 08:19:02 -0400
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Aidan MacDonald <aidanmacdonald.0x0@...il.com>
Cc:     broonie@...nel.org, lgirdwood@...il.com, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org,
        kuninori.morimoto.gx@...esas.com, perex@...ex.cz, tiwai@...e.com,
        alsa-devel@...a-project.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/2] dt-bindings: ASoC: simple-card: Add
 system-clock-id property

On 25/10/2022 05:14, Aidan MacDonald wrote:
>> Krzysztof
> 
> Device trees already use standardized enumerations in other areas so it
> isn't a new idea. Look under include/dt-bindings/clock. Every header
> there contains an arbitrary enumeration of a device's clocks. In fact
> most of include/dt-bindings is exactly for this purpose, to define
> standard values that are not "just numbers" but an enum, a flag, etc,
> with a special meaning. It is not specific to clocks.
> 
> There is no dt-binding for system clock ID, because prior to this patch
> they were not exposed to DT in any way. But the enumerations themselves
> already exist, eg. the IDs for nau8821 codec:
> 
>     /* System Clock Source */
>     enum {
>         NAU8821_CLK_DIS,
>         NAU8821_CLK_MCLK,
>         NAU8821_CLK_INTERNAL,
>         NAU8821_CLK_FLL_MCLK,
>         NAU8821_CLK_FLL_BLK,
>         NAU8821_CLK_FLL_FS,
>     };

OK, this looks good.

> 
> We would just be moving these into dt-bindings if somebody wants to
> use a codec with simple-card. Future drivers would add the enum into
> dt-bindings from the start because that's where it belongs.

And the remaining piece I don't get is that these are not bindings for
codec, but for sound audio card. You want to set "system-clock-id"
property for audio card, while putting clock from codec, which will be
used to pass back to the codec... so it is a property of the codec, not
of the audio card. IOW, NAU8821_CLK_* does not configure here the clock
of the system, but only, only clock of the codec.



Best regards,
Krzysztof