linux-kernel - Re: [PATCH v4 1/5] dt-bindings: watchdog: mt7621-wdt: add phandle to access system controller registers

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Message-ID: <CAMhs-H-rKmks4xL-nK8BF7RtRxX95aYhH6VUpvy_bR1-=-xdLg@mail.gmail.com>
Date:   Mon, 13 Feb 2023 09:58:19 +0100
From:   Sergio Paracuellos <sergio.paracuellos@...il.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Arınç ÜNAL <arinc.unal@...nc9.com>,
        linux-watchdog@...r.kernel.org, wim@...ux-watchdog.org,
        linux@...ck-us.net, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, matthias.bgg@...il.com,
        tsbogend@...ha.franken.de, p.zabel@...gutronix.de,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-mips@...r.kernel.org
Subject: Re: [PATCH v4 1/5] dt-bindings: watchdog: mt7621-wdt: add phandle to
 access system controller registers

On Mon, Feb 13, 2023 at 9:38 AM Krzysztof Kozlowski
<krzysztof.kozlowski@...aro.org> wrote:
>
> On 12/02/2023 09:13, Sergio Paracuellos wrote:
> > On Sat, Feb 11, 2023 at 12:42 PM Krzysztof Kozlowski
> > <krzysztof.kozlowski@...aro.org> wrote:
> >>
> >> On 11/02/2023 12:01, Sergio Paracuellos wrote:
> >>> On Sat, Feb 11, 2023 at 11:47 AM Arınç ÜNAL <arinc.unal@...nc9.com> wrote:
> >>>>
> >>>> On 11.02.2023 13:41, Sergio Paracuellos wrote:
> >>>>> On Sat, Feb 11, 2023 at 10:10 AM Arınç ÜNAL <arinc.unal@...nc9.com> wrote:
> >>>>>>
> >>>>>> Is this mediatek,sysctl property required after your changes on the
> >>>>>> watchdog code?
> >>>>>
> >>>>> I don't really understand the question :-) Yes, it is. Since we have
> >>>>> introduced a new phandle in the watchdog node to be able to access the
> >>>>> reset status register through the 'sysc' syscon node.
> >>>>> We need the bindings to be aligned with the mt7621.dtsi file and we
> >>>>> are getting the syscon regmap handler via
> >>>>> 'syscon_regmap_lookup_by_phandle()'. See PATCH 5 of the series, Arınç.
> >>>>
> >>>> I believe you need to put mediatek,sysctl under "required:".
> >>>
> >>> Ah, I understood your question now :-). You meant 'required' property.
> >>> I need more coffee, I guess :-). I am not sure if you can add
> >>> properties as required after bindings are already mainlined for
> >>> compatibility issues. The problem with this SoC is that drivers become
> >>> mainlined before the device tree was so if things are properly fixed
> >>> now this kind of issues appear.  Let's see Krzysztof and Rob comments
> >>> for this.
> >>
> >> If your driver fails to probe without mediatek,sysctl, you already made
> >> it required (thus broke the ABI) regardless what dt-binding is saying.
> >> In such case you should update dt-binding to reflect reality.
> >>
> >> Now ABI break is different case. Usually you should not break it without
> >> valid reasons (e.g. it was never working before). Your commit msg
> >> suggests that you only improve the code, thus ABI break is not really
> >> justified. In such case - binding is correct, driver should be reworked
> >> to accept DTS without the new property.
> >
> > Thanks for clarification, Krzysztof. Ok, so if this is the case I need
> > to add this property required (as Arinc was properly pointing out in
> > previous mail) since without it the driver is going to fail on probe
> > (PATCH 5 of the series). I understand the "it was never working
> > before" argument reason for ABI breaks. What happens if the old driver
> > code was not ideal and totally dependent on architecture specific
> > operations when this could be totally avoided and properly make arch
> > independent agnostic drivers?
>
> It's just an improvement and improvements should be incremental and not
> break ABI.

Understood.

>
> > This driver was added in 2016 [0]. There
> > was not a device tree file in the kernel for this SoC mainlined until
> > 2022 [1].
>
> 2022 march was almost a year ago, so there were kernel releases with
> this ABI.
>
> Also, what about all out of tree DTS? What about other operating
> systems, bootloaders, firmwares etc?

Pretty clear, thanks. So I guess I have to drop all the changes that
are breaking ABI and just maintain those that make no real changes in
bindings.

>
>
> Best regards,
> Krzysztof

Thanks,
    Sergio Paracuellos
>