linux-kernel - Re: [PATCH v2 devicetree] Revert "arm64: dts: freescale: Fix 'interrupt-map' parent address cells"

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Date:   Mon, 14 Mar 2022 10:08:33 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Vladimir Oltean <vladimir.oltean@....com>,
        devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Shawn Guo <shawnguo@...nel.org>, Li Yang <leoyang.li@....com>,
        Biwen Li <biwen.li@....com>,
        Zhiqiang Hou <Zhiqiang.Hou@....com>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v2 devicetree] Revert "arm64: dts: freescale: Fix
 'interrupt-map' parent address cells"

On Mon, Mar 14, 2022 at 9:34 AM Marc Zyngier <maz@...nel.org> wrote:
>
> On Mon, 14 Mar 2022 15:15:15 +0000,
> Rob Herring <robh+dt@...nel.org> wrote:
> >
> > On Tue, Dec 14, 2021 at 6:59 AM Vladimir Oltean <vladimir.oltean@....com> wrote:
> > > Therefore, the premise of the patch being reverted here is invalid.
> > > It doesn't matter whether the driver, in its non-standard use of the
> > > property, complies to the standard format or not, since this property
> > > isn't expected to be used for interrupt translation by the core.
> >
> > I disagree. The non-standard part is that 'interrupt-map' translation
> > is not transparent. 'interrupt-map' that can't be parsed in the
> > standard way is just wrong, and I imagine was never the intention
> > here. We simply cannot have platforms defining their own format for
> > standard properties.
>
> That ship sailed a long while ago. We have a list of offenders, and we
> can make sure we don't get additional ones.
>
> > Reverting this will cause dtc warnings now (IIRC) and just kicks the
> > can down the road. Reverting is fine for now (I gave Arnd the okay on
> > IRC), but I think the parsing will need to be updated to honor
> > #address-cells and detect an old DT (probably by looking at the total
> > size of 'interrupt-map') and mark that change for stable. That would
> > only leave a new dt with an old kernel without stable updates broken.
> > Seems unlikely a device is getting firmware updates, but not OS
> > updates.
>
> Being able to rollback firmware and OS independently is important. The
> tooling can be taught about the broken instances, which should be
> enough.  Adding to the parsing only makes things harder to maintain,
> for no real gain.

It's up to individual platforms to care about that. If they don't,
then compatibility has been broken multiple times most certainly
because in general there is 0 testing for it. Why make our lives more
complicated in those cases?

Rob