Re: [PATCH v3 01/20] dt-bindings: arm: gic: Allow combining arm,gic-400 compatible strings

From: Rob Herring <robh@kernel.org>
To: "André Przywara" <andre.przywara@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
	<devicetree@vger.kernel.org>,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	Marc Zyngier <maz@kernel.org>, Liviu Dudau <liviu.dudau@arm.com>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Sudeep Holla <sudeep.holla@arm.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v3 01/20] dt-bindings: arm: gic: Allow combining arm,gic-400 compatible strings
Date: Tue, 26 May 2020 09:49:38 -0600	[thread overview]
Message-ID: <CAL_JsqJpe_EMC4cqXVtxY9XVrVfqDNU3=-1_47wmirFLtA1Lcg@mail.gmail.com> (raw)
In-Reply-To: <6e2cc3e9-b14f-2b50-0390-addcc82389e0@arm.com>

On Tue, May 19, 2020 at 3:20 AM André Przywara <andre.przywara@arm.com> wrote:
>
> On 19/05/2020 08:39, Geert Uytterhoeven wrote:
>
> Hi Geert,
>
>
> > On Wed, May 13, 2020 at 12:31 PM Andre Przywara <andre.przywara@arm.com> wrote:
> >> The arm,gic-400 compatible is probably the best matching string for the
> >> GIC in most modern SoCs, but was only introduced later into the kernel.
> >> For historic reasons and to keep compatibility, some SoC DTs were thus
> >> using a combination of this name and one of the older strings, which
> >> currently the binding denies.
> >>
> >> Add a stanza to the DT binding to allow "arm,gic-400", followed by
> >> either "arm,cortex-a15-gic" or "arm,cortex-a7-gic". This fixes binding
> >> compliance for quite some SoC .dtsi files in the kernel tree.
> >>
> >> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> >
> > Thanks for your patch, I was just looking into this issue ;-)
> >
> >> --- a/Documentation/devicetree/bindings/interrupt-controller/arm,gic.yaml
> >> +++ b/Documentation/devicetree/bindings/interrupt-controller/arm,gic.yaml
> >> @@ -39,6 +39,12 @@ properties:
> >>                - qcom,msm-8660-qgic
> >>                - qcom,msm-qgic2
> >>
> >> +      - items:
> >> +          - const: arm,gic-400
> >> +          - enum:
> >> +             - arm,cortex-a15-gic
> >> +             - arm,cortex-a7-gic
> >> +
> >>        - items:
> >>            - const: arm,arm1176jzf-devchip-gic
> >>            - const: arm,arm11mp-gic
> >
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/r9a06g032.dtsi#n177
> > has them in the other order.
> >
> > What do you think is the preferred solution: reverting the order, or dropping
> > one or the other?
>
> Reverting the order would be the right thing. Theoretically this might
> change what the drivers match against, but there should be no difference
> between those strings anyway. And certainly Linux does not care which of
> the many strings it sees.
>
> The proper order is not really obvious here, but the cortex-a{15,7}-gic
> names serve as the missing "arm,gic-v2" generic fallback string here, I
> think just for historical reasons.

Really, they probably should have been mutually exclusive given an
implementation has one or the other. Since we have both, the order in
the schema is correct given gic-400 is a superset (multi-cluster) and
the compatible came later in time.

Rob

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