linux-kernel - Re: [RFC PATCH 4/7] irqchip/apple-aic: Add support for Apple AIC

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Date:   Thu, 21 Jan 2021 11:45:51 -0600
From:   Rob Herring <robh@...nel.org>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Marc Zyngier <maz@...nel.org>,
        Hector Martin <marcan@...can.st>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Mohamed Mediouni <mohamed.mediouni@...amail.com>,
        Will Deacon <will@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Stan Skowronek <stan@...ellium.com>
Subject: Re: [RFC PATCH 4/7] irqchip/apple-aic: Add support for Apple AIC

On Thu, Jan 21, 2021 at 4:38 AM Arnd Bergmann <arnd@...nel.org> wrote:
>
> On Thu, Jan 21, 2021 at 10:48 AM Linus Walleij <linus.walleij@...aro.org> wrote:
> >
> > Hi Mohamed,
> >
> > thanks for your patch!
> >
> > On Wed, Jan 20, 2021 at 2:31 PM Mohamed Mediouni
> > <mohamed.mediouni@...amail.com> wrote:
> >
> > > +properties:
> > > +  compatible:
> > > +    items:
> > > +      - const: apple,aic
> >
> > However weird it may seem, Apple is not in the file
> > Documentation/devicetree/bindings/vendor-prefixes.yaml
> >
> > (I think it's weird because I remember clearly that they have been
> > using device tree for PPC since ages.)
> >
> > Could you add this 2-liner to that file and send it directly to
> > DT binding maintainers as a single patch as a preparation?
>
> Choosing the vendor prefix here is going to be a little tricky
> and non-obvious.
>
> Background:
>
> Traditionally, it should have been the stock ticker symbol of the
> company (clearly only publicly traded companies would be able
> to produce a Unix capable computer, right?), but there were
> already inconsistent: IBM used "ibm" (in small letters), Sun
> used "SUNW" (in capitals) but in 2007 changed the stock ticker
> symbol to "JAVA", obviously without changing the firmware bindings.
>
> Apple traditionally used "AAPL" (also in caps) in the device tree,
> and there is one remnant of that in the M1 device tree, in the form
> of the "AAPL,phandle" property in each node, which corresponds
> to our "linux,phandle". (phandles were introduced as properties in
> both of the flattened DT formats, .dtb and apple's own format).
> There are also "AAPL,unit-string properties and some device_type
> strings (AAPL,display-crossbar, AAPL,atc-dpxbar, ...) in the M1 DT,
> and the CPU nodes (and only those) use "apple" in small letters
> as in "apple,icestorm","ARM,v8". The other nodes tend to not have
> a vendor prefix, but a lot use a subsystem name as the prefix, such
> as compatible="gpio,t8101" or compatible="tempsensor,t8020".
>
> Since Apple are already using both the "AAPL" and the "apple"
> prefix themselves, I have a bad feeling about reusing either of
> them for defining the devicetree.org bindings that we add to
> linux/Documentation/devicetree/bindings. The question is: if
> not "apple", what else should we use here?

IMO, 'AAPL' as that is what is already in use in the kernel. I don't
see why it matters at all what Apple is using. It might if we used any
of the ADT as-is, but I don't see that happening from what I've seen.

Rob