linux-kernel - Re: [PATCH 2/5] ASoC: dt-bindings: document WCD939x Audio Codec

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Date:   Tue, 28 Nov 2023 10:14:29 +0100
From:   neil.armstrong@...aro.org
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Banajit Goswami <bgoswami@...cinc.com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>
Cc:     linux-arm-msm@...r.kernel.org, alsa-devel@...a-project.org,
        linux-sound@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] ASoC: dt-bindings: document WCD939x Audio Codec

On 28/11/2023 10:04, Krzysztof Kozlowski wrote:
> On 28/11/2023 09:59, Neil Armstrong wrote:
>> On 24/11/2023 09:33, Krzysztof Kozlowski wrote:
>>> On 23/11/2023 15:49, Neil Armstrong wrote:
>>>
>>>> +  Qualcomm WCD9390/WCD9395 Codec is a standalone Hi-Fi audio codec IC.
>>>> +  It has RX and TX Soundwire slave devices.
>>>> +  The WCD9390/WCD9395 IC has a functionally separate USB-C Mux subsystem
>>>> +  accessible over an I2C interface.
>>>> +  The Audio Headphone and Microphone data path between the Codec and the USB-C Mux
>>>> +  subsystems are external to the IC, thus requiring DT port-endpoint graph description
>>>> +  to handle USB-C altmode & orientation switching for Audio Accessory Mode.
>>>> +
>>>> +allOf:
>>>> +  - $ref: dai-common.yaml#
>>>> +  - $ref: qcom,wcd93xx-common.yaml#
>>>> +
>>>> +properties:
>>>> +  compatible:
>>>> +    enum:
>>>> +      - qcom,wcd9390-codec
>>>> +      - qcom,wcd9395-codec
>>>
>>> 9395 should be compatible with 9390, so please express it with a list
>>> using fallback. I know that earlier wcd93xx do not follow that concept,
>>> but maybe we will fix them some point as well.
>>
>> I don't get why this would be needed, yes their are compatible but still
>> two separate ICs with different internal capabilities.
>>
>> It the first time I get such request for new documentation
> 
> Maybe it is first time for you, but I ask about this all the time. What
> is important is whether the programming model or how the OS uses the
> device is the same.

I agree for new version of HW, anyway..

> 
> Here the device exposes its version in registers, so you can easily rely
> on the compatibility. That's also the case multiple times talked on the
> mailing lists.

... you're right here version can be determined at runtime.

But, since both are compatible, there's no primary part number, right?

so why use "qcom,wcd9395-codec", "qcom,wcd9390-codec"
when "qcom,wcd9390-codec", "qcom,wcd9395-codec" should
also be valid, so in this can why not use :
"qcom,wcd9390-codec", "qcom,wcd939x-codec"
or
"qcom,wcd9395-codec", "qcom,wcd939x-codec"

?

> 
> Best regards,
> Krzysztof
>