linux-kernel - Re: [PATCH v1] Documentation/process: add soc maintainer handbook

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Message-Id: <3B8DFBEF-9EA1-4375-998D-944EA18D3E4E@jrtc27.com>
Date:   Tue, 23 May 2023 01:32:49 +0100
From:   Jessica Clarke <jrtc27@...c27.com>
To:     Conor Dooley <conor@...nel.org>
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        soc@...nel.org, Conor Dooley <conor.dooley@...rochip.com>,
        Arnd Bergmann <arnd@...db.de>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Olof Johansson <olof@...om.net>,
        Palmer Dabbelt <palmer@...belt.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-doc@...r.kernel.org,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v1] Documentation/process: add soc maintainer handbook

On 22 May 2023, at 22:34, Conor Dooley <conor@...nel.org> wrote:
> 
> On Tue, May 16, 2023 at 10:31:19AM +0200, Krzysztof Kozlowski wrote:
>> On 15/05/2023 21:20, Conor Dooley wrote:
> 
>>> +devicetree ABI stability
>>> +~~~~~~~~~~~~~~~~~~~~~~~~
>>> +
>>> +Perhaps one of the most important things to highlight is that dt-bindings
>>> +document the ABI between the devicetree and the kernel.  Once dt-bindings have
>>> +been merged (and appear in a release of the kernel) they are set in stone, and
>>> +any changes made must be compatible with existing devicetrees.  This means that,
>>> +when changing properties, a "new" kernel must still be able to handle an old
>>> +devicetree.  For many systems the devicetree is provided by firmware, and
>>> +upgrading to a newer kernel cannot cause regressions.  Ideally, the inverse is
>>> +also true, and a new devicetree will also be compatible with an old kernel,
>>> +although this is often not possible.
>> 
>> I would prefer to skip it and instead: enhance
>> Documentation/devicetree/bindings/ABI.rst and then reference it here.
>> 
>>> +
>>> +If changes are being made to a devicetree that are incompatible with old
>>> +kernels, the devicetree patch should not be applied until the driver is, or an
>>> +appropriate time later.  Most importantly, any incompatible changes should be
>>> +clearly pointed out in the patch description and pull request, along with the
>>> +expected impact on existing users.
> 
> I'm not really sure that I like this truncated section so much, but here
> it is... I kept the last paragraph intact as it does not talk about the
> ABI, but rather exceptions of submaintainers.
> 
> devicetree ABI stability
> ~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Perhaps one of the most important things to highlight is that dt-bindings
> document the ABI between the devicetree and the kernel. Please see
> :ref:`devicetree-abi` for devicetree ABI rules.
> 
> If changes are being made to a devicetree that are incompatible with old
> kernels, the devicetree patch should not be applied until the driver is, or an
> appropriate time later.  Most importantly, any incompatible changes should be
> clearly pointed out in the patch description and pull request, along with the
> expected impact on existing users.

Do you have an opinion on acknowledging the existence of other OSes here?

Jess