linux-kernel - Re: [PATCH v1 1/3] dt-bindings: mmc: Drop unused properties

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Message-ID: <CAJM55Z8XowmB-Hfzr+hBtWu+SGL2v7jya6Nx5_rATf8=5qA4Fg@mail.gmail.com>
Date:   Fri, 8 Sep 2023 15:32:36 +0200
From:   Emil Renner Berthing <emil.renner.berthing@...onical.com>
To:     William Qiu <william.qiu@...rfivetech.com>
Cc:     Conor Dooley <conor@...nel.org>,
        Jessica Clarke <jrtc27@...c27.com>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        linux-mmc@...r.kernel.org, Emil Renner Berthing <kernel@...il.dk>,
        Rob Herring <robh+dt@...nel.org>,
        Jaehoon Chung <jh80.chung@...sung.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>
Subject: Re: [PATCH v1 1/3] dt-bindings: mmc: Drop unused properties

On Fri, 8 Sept 2023 at 12:03, William Qiu <william.qiu@...rfivetech.com> wrote:
> On 2023/9/2 1:43, Conor Dooley wrote:
> > On Fri, Sep 01, 2023 at 06:20:38PM +0100, Jessica Clarke wrote:
> >> On 1 Sep 2023, at 16:42, Conor Dooley <conor@...nel.org> wrote:
> >> >
> >> > On Fri, Sep 01, 2023 at 10:33:13AM +0800, William Qiu wrote:
> >> >>
> >> >>
> >> >> On 2023/8/30 16:34, Conor Dooley wrote:
> >> >>> On Wed, Aug 30, 2023 at 09:29:20AM +0200, Krzysztof Kozlowski wrote:
> >> >>>> On 30/08/2023 08:50, Conor Dooley wrote:
> >> >>>>> On Wed, Aug 30, 2023 at 11:18:44AM +0800, William Qiu wrote:
> >> >>>>>> Due to the change of tuning implementation, it's no longer necessary to
> >> >>>>>> use the "starfive,sysreg" property in dts, so drop the relevant
> >> >>>>>> description in dt-bindings here.
> >> >>>>>
> >> >>>>> How does changing your software implantation invalidate a description of
> >> >>>>> the hardware?
> >> >>>>>
> >> >>>>
> >> >>>> Which is kind of proof that this syscon was just to substitute
> >> >>>> incomplete hardware description (e.g. missing clocks and phys). We
> >> >>>> should have rejected it. Just like we should reject them in the future.
> >> >>>
> >> >>> :s I dunno what to do with this... I'm inclined to say not to remove it
> >> >>> from the binding or dts at all & only change the software.
> >> >>>
> >> >>>> There are just few cases where syscon is reasonable. All others is just
> >> >>>> laziness. It's not only starfivetech, of course. Several other
> >> >>>> contributors do the same.
> >> >>>
> >> >>> I'm not sure if laziness is fair, lack of understanding is usually more
> >> >>> likely.
> >> >>
> >> >> For this, I tend to keep it in binding, but remove it from required. Because
> >> >> we only modify the tuning implementation, it doesn't mean that this property
> >> >> need to be removed, it's just no longer be the required one.
> >> >
> >> > Please only remove it from required if the current driver doesn't break
> >> > if the regmap is removed.
> >>
> >> Either way please make sure the documentation clearly states “never use
> >> this, if you’re using it you’re doing it wrong, this only exists
> >> because it was wrongly used in the past”. Otherwise people writing
> >> drivers for other OSes will probably use it too thinking they need to.
> >
> > Maybe we should just delete it if the impact is going to be negligible,
> > sounds like you're not using it in FreeBSD, which was part of what I was
> > worried about. Guess it depends on what Emil & the distro heads think.
> Hi Conor,
>
> After discussing it with our colleagues, we decided that deleting it was the best
> course of action. Since there will no longer be a related implementation of
> "starfive,sysreg" in future drivers, even if the dt-binding is described, it will
> be "never use", so I think it should be deleted.
>
> What do you think?

The device tree should be a description of the hardware and there
really is a 'u0_sdio_data_strobe_phase_ctrl' field in the sysreg
registers[1] on the JH7110 that seems to do _something_ related to the
sdio interface. So I don't think the fact that the Linux driver no
longer uses it is a good reason to remove it, but if there are some
other pragmatic reasons to do so then I'm fine with it. Removing it
from the list of required properties should be fine though.

/Emil

[1]: https://doc-en.rvspace.org/JH7110/TRM/JH7110_TRM/sys_syscon.html