linux-kernel - Re: [PATCH v2 08/12] ARM: dts: imx6dl-pico: fix board compatibles

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Message-ID: <784e0528-f4c1-5c0f-44e8-b19afbffe3ba@pengutronix.de>
Date:   Fri, 2 Oct 2020 10:34:29 +0200
From:   Ahmad Fatoum <a.fatoum@...gutronix.de>
To:     Krzysztof Kozlowski <krzk@...nel.org>
Cc:     Rob Herring <robh+dt@...nel.org>, Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Anson Huang <Anson.Huang@....com>,
        Andreas Kemnade <andreas@...nade.info>,
        Stefan Riedmueller <s.riedmueller@...tec.de>,
        Robert Jones <rjones@...eworks.com>,
        Li Yang <leoyang.li@....com>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 08/12] ARM: dts: imx6dl-pico: fix board compatibles

Hello,

On 10/2/20 10:20 AM, Krzysztof Kozlowski wrote:
> On Fri, Oct 02, 2020 at 09:41:28AM +0200, Ahmad Fatoum wrote:
>> Hello,
>>
>> On 10/1/20 12:37 PM, Krzysztof Kozlowski wrote:
>>>> The existing binding doesn't cover these boards then and needs to be
>>>> extended, no? How about following patch?
>>>
>>> What do you mean it doesn't cover? It was added exactly to handle them:
>>> +              - technexion,imx6q-pico-dwarf   # TechNexion i.MX6Q Pico-Dwarf
>>> +              - technexion,imx6q-pico-hobbit  # TechNexion i.MX6Q Pico-Hobbit
>>> +              - technexion,imx6q-pico-nymph   # TechNexion i.MX6Q Pico-Nymph
>>> +              - technexion,imx6q-pico-pi      # TechNexion i.MX6Q Pico-Pi
>>>
>>
>> Still they are unused. So I'd think these boards should be handled like boards
>> that predated bindings: a binding is written that doesn't break existing users.
> 
> OK, let's assume the binding is not correct and DTSes are good.
> 
>>
>>>> [I guess we need to keep the two-compatible list they were originally
>>>>  in for compatibility even if it's unused among upstream device trees?]
>>>
>>> You want to change both the binding (thus breaking the ABI) and update
>>> the DTS to reflect new ABI. Then why having a binding at all?
>>
>> If we leave the old two-compatible enumeration intact, there is no ABI broken.
> 
> Just to clarify, because I don't get here the "no ABI broken" part:
> ABI is the binding, not the DTS. We can change intree DTS as we like,
> replace compatibles, add nodes, remove nodes. There is no stability
> requirement for DTS contents.
> If we leave two-compatible binding intact, it is a broken binding since
> beginning. Removing non-working, fake ABI is not breaking it because it
> could never work.

Then I misunderstood you. I was thinking about possible out-of-tree users
that have boards based on this and are adhering to the binding. Dropping
the binding would break those (albeit it's a quite manageable form of
brokenness here).

>>> I would assume that either binding is correct or DTS. You propose that
>>> both are wrong and both need changes... in such case this is clearly
>>> broken.
>>
>> IMO the DTS is the correct one. If you want to honor the author's intention
>> that each base board has a different compatible, it should be an extra
>> compatible and not replace the existing one that may be already in use.
> 
> OK, we can go with DTS approach. I fixed few of such cases as well,
> assuming that DTS was intended and binding was incorrect. In such case
> all boards will be documented under one compatible technexion,imx6q-pico
> and DTS will not be changed.

Sounds good. If further differentiation proves to be needed, it can be a
new compatible added in a separate commit.

Thanks
Ahmad

> 
> Best regards,
> Krzysztof
> 

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