linux-kernel - Re: [PATCH v2 2/2] spi: npcm-pspi: Add NPCM845 peripheral SPI support

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Date:   Wed, 27 Jul 2022 08:51:11 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Tomer Maimon <tmaimon77@...il.com>
Cc:     Mark Brown <broonie@...nel.org>,
        Avi Fishman <avifishman70@...il.com>,
        Tali Perry <tali.perry1@...il.com>,
        Joel Stanley <joel@....id.au>,
        Patrick Venture <venture@...gle.com>,
        Nancy Yuen <yuenn@...gle.com>,
        Benjamin Fair <benjaminfair@...gle.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        OpenBMC Maillist <openbmc@...ts.ozlabs.org>,
        linux-spi@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] spi: npcm-pspi: Add NPCM845 peripheral SPI support

On 26/07/2022 21:32, Tomer Maimon wrote:
> Hi Krzysztof,
> 
> Thanks for your explanation.
> 
> On Tue, 26 Jul 2022 at 12:47, Krzysztof Kozlowski
> <krzysztof.kozlowski@...aro.org> wrote:
>>
>> On 24/07/2022 10:44, Tomer Maimon wrote:
>>> Hi Mark and Krzysztof,
>>>
>>> Thanks for your reply,
>>>
>>> On Fri, 22 Jul 2022 at 21:57, Mark Brown <broonie@...nel.org> wrote:
>>>>
>>>> On Fri, Jul 22, 2022 at 08:47:24PM +0200, Krzysztof Kozlowski wrote:
>>>>> On 22/07/2022 20:43, Mark Brown wrote:
>>>>
>>>>>> ...with a fallback list required by the bindings so the driver actually
>>>>>> binds.  Note that bindings are currently not in YAML format so there'd
>>>>>> be even less enforcement of that than normal, and as they're currently
>>>>>> written the bindings don't require fallback.
>>>>
>>>>> Yes, the bindings document should be rephrased but we were living like
>>>>> that for few years. :)
>>>>
>>>> The binding document as it stands only has one compatible, there's no
>>>> existing problem with it other than the YAML conversion.  If we're
>>>> adding something new that requires a fallback we should be explicit
>>>> about that rather than have something that's actively misleading where
>>>> previously things were clear.  I don't mind if we add the compatible to
>>>> the driver or document the requirement for the fallback but we should do
>>>> one of the two.
>>>
>>> is V2 good enough? adding the compatible to the driver and the document?
>>> Or should we use fallback?
>>> If fallback is choosen, can you explain how I should do it?
>>
>> I propose to use fallback. The preferred way is to convert it to DT
>> schema and then add new device support (so two commits). Other
>> acceptable way is to rephrase the TXT so it clearly states desired
>> compatibles - one for old device, two for new devices. There are plenty
>> of examples in current sources.
> Appreciate if you could clarify.
> in case we use DT-schema, we dont describe the fallback like we doing
> in txt document?
> I mean that in the yaml file we should describe the NPCM PSPI
> compatible property as follow:
>   compatible:
>     enum:
>       - nuvoton,npcm750-pspi
>       - nuvoton,npcm845-pspi
> 
> If yes, how should the user know that he needs to use fallback incase
> is using nuvoton,npcm845-pspi? only from the device tree?
>

If you use DT schema format, you must code it as with fallback (so
items). This is the most popular setup for SoC components so you will
easily find such examples.


Best regards,
Krzysztof