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

[Guenter Roeck]

On Mon, Feb 13, 2023 at 09:59:35AM +0100, Sergio Paracuellos wrote:
> On Sun, Feb 12, 2023 at 4:27 PM Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> >
> > On 2/12/23 00:13, Sergio Paracuellos wrote:
> > > On Sat, Feb 11, 2023 at 12:42 PM Krzysztof Kozlowski
> > > <krzysztof.kozlowski@xxxxxxxxxx> wrote:
> > >>
> > >> On 11/02/2023 12:01, Sergio Paracuellos wrote:
> > >>> On Sat, Feb 11, 2023 at 11:47 AM Arınç ÜNAL <arinc.unal@xxxxxxxxxx> wrote:
> > >>>>
> > >>>> On 11.02.2023 13:41, Sergio Paracuellos wrote:
> > >>>>> On Sat, Feb 11, 2023 at 10:10 AM Arınç ÜNAL <arinc.unal@xxxxxxxxxx> 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? This driver was added in 2016 [0]. There
> > > was not a device tree file in the kernel for this SoC mainlined until
> > > 2022 [1]. I also personally migrated this watchdog binding in 2022
> > > from text to YAML and maintained it without changes [2]. When this was
> > > mainlined not all drivers were properly reviewed and the current code
> > > was just maintained as it is. Most users of this SoC are in the
> > > openWRT community where the dtsi of the mainline is not used yet and
> > > they maintain their own mt7621.dtsi files. Also, when a new version of
> > > the openWRT selected kernel is added they also modify and align with
> > > its mt7621.dtsi file without maintaining previous dtb's. If "make the
> > > driver arch independent to be able to be compile tested" and this kind
> > > of arguments are not valid at all I need to know because I have
> > > started to review driver code for this SoC and other drivers also have
> > > the same arch dependency that ideally should be avoided in the same
> > > way. This at the end means to break the ABI again in the future for
> > > those drivers / bindings. So I can just let them be as it is and not
> > > provide any change at all and continue without being compile tested
> > > and other beneficial features to detect future driver breakage.
> > >
> >
> > Problem is that there are (presumably) shipped systems out there with
> > the old devicetree file. The watchdog driver would no longer instantiate
> > on those systems.
> 
> Ok, I will maintain only the PATCH that changes the driver to not use
> globals and send v5.
> 

Other options might be to search for the "syscon" node name or to search
for the "mediatek,mt7621-sysc" compatible.

Guenter

> >
> > Guenter
> >
> 
> Thanks,
>     Sergio Paracuellos