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

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Date:   Fri, 2 Oct 2020 09:41:28 +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 10/1/20 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.

>> [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.

> 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.

Cheers
Ahmad


> 
> Best regards,
> Krzysztof
> 

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