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

From: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
To: Herve Codina <herve.codina@bootlin.com>
Cc: Rob Herring <robh+dt@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Liam Girdwood <lgirdwood@gmail.com>,
	Mark Brown <broonie@kernel.org>,
	Derek Kiernan <derek.kiernan@xilinx.com>,
	Dragan Cvetic <dragan.cvetic@xilinx.com>,
	Arnd Bergmann <arnd@arndb.de>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Takashi Iwai <tiwai@suse.com>,
	linux-kernel@vger.kernel.org, devicetree@vger.kernel.org,
	alsa-devel@alsa-project.org,
	Christophe Leroy <christophe.leroy@csgroup.eu>,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Subject: Re: [PATCH v2 5/7] dt-bindings: sound: Add support for the Lantiq PEF2256 codec
Date: Mon, 20 Mar 2023 19:21:39 +0100	[thread overview]
Message-ID: <f8227202-95ba-7dae-8f41-2023d7a08691@linaro.org> (raw)
In-Reply-To: <20230320191700.3d48e264@bootlin.com>

On 20/03/2023 19:17, Herve Codina wrote:
> Hi Krzysztof
> 
> On Fri, 17 Mar 2023 09:57:11 +0100
> Krzysztof Kozlowski <krzysztof.kozlowski@linaro.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