linux-kernel - Re: [PATCH v2 5/7] dt-bindings: sound: Add support for the Lantiq PEF2256 codec

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Date:   Mon, 20 Mar 2023 19:21:39 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Herve Codina <herve.codina@...tlin.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Derek Kiernan <derek.kiernan@...inx.com>,
        Dragan Cvetic <dragan.cvetic@...inx.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, alsa-devel@...a-project.org,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v2 5/7] dt-bindings: sound: Add support for the Lantiq
 PEF2256 codec

On 20/03/2023 19:17, Herve Codina wrote:
> Hi Krzysztof
> 
> On Fri, 17 Mar 2023 09:57:11 +0100
> Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org> wrote:
> 
>> On 16/03/2023 13:27, Herve Codina wrote:
>>> The Lantiq PEF2256, also known as Infineon PEF2256 or FALC256, is a
>>> framer and line interface component designed to fulfill all required
>>> interfacing between an analog E1/T1/J1 line and the digital PCM system
>>> highway/H.100 bus.
>>>
>>> The codec support allows to use some of the PCM system highway
>>> time-slots as audio channels to transport audio data over the E1/T1/J1
>>> lines.
>>>   
>>
>> Your other file should also have specific compatible, unless this codec
>> is actually part of the framer. Did not look like this in the binding -
>> not $ref.
> 
> No sure to understand what you mean.

Compatible "lantiq,pef2256" in the context of this file is confusing.
Two devices without parent-child having similar but different
compatibles, of which one is generic (covers entire device) and one is
function (codec) specific.


> 
> Anyway, I plan to use a MFD device for pef2256 and reference this yaml
> from the lantiq,pef2256.yaml in the node related to the codec.

It should be part of these series. Submit complete bindings.

> 
> One question related to bindings and related checks:
> Is there a way to check the compatible property of the parent node.
> I mean, here is the binding of a child node of a MFD node.
> From this binding, I would like to be sure that the parent is really a
> pef2256 MFD node.

You cannot and you shouldn't. Parent checks children, not vice-versa.

> 
> May be something like:
>   parent-properties:
>     allOf:
>       compatible:
>         contains:
>           const: lantiq,pef2256
> 
> The idea is to have dtbs_check raise an error if the parent's compatible
> property is not 'lantiq,pef2256'.

But it does not matter. Why your device cannot be used in
lantiq,foobar-9999?


Best regards,
Krzysztof