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From:   Rob Herring <robh@kernel.org>
Date:   Tue, 14 Jul 2020 08:22:43 -0600
Message-ID: <CAL_JsqKg4CfGPxf-SzVevCaY0NU63oR+pqSqdV0aG+EaecGbvg@mail.gmail.com>
Subject: Re: [PATCH v10 4/5] dt-bindings: arm-smmu: add binding for Tegra194 SMMU
To:     Robin Murphy <robin.murphy@arm.com>
Cc:     Krishna Reddy <vdumpa@nvidia.com>,
        "joro@8bytes.org" <joro@8bytes.org>,
        "will@kernel.org" <will@kernel.org>,
        Thierry Reding <treding@nvidia.com>,
        Jonathan Hunter <jonathanh@nvidia.com>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-tegra@vger.kernel.org" <linux-tegra@vger.kernel.org>,
        Yu-Huan Hsu <YHsu@nvidia.com>,
        Sachin Nikam <Snikam@nvidia.com>,
        Pritesh Raithatha <praithatha@nvidia.com>,
        Timo Alho <talho@nvidia.com>,
        Bitan Biswas <bbiswas@nvidia.com>,
        Mikko Perttunen <mperttunen@nvidia.com>,
        Nicolin Chen <nicolinc@nvidia.com>,
        Bryan Huntsman <bhuntsman@nvidia.com>,
        "nicoleotsuka@gmail.com" <nicoleotsuka@gmail.com>
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On Mon, Jul 13, 2020 at 8:10 AM Robin Murphy <robin.murphy@arm.com> wrote:
>
> On 2020-07-10 21:29, Krishna Reddy wrote:
> > Thanks Rob. One question on setting "minItems: ". Please see below.
> >
> >>> +allOf:
> >>> +  - if:
> >>> +      properties:
> >>> +        compatible:
> >>> +          contains:
> >>> +            enum:
> >>> +              - nvidia,tegra194-smmu
> >>> +    then:
> >>> +      properties:
> >>> +        reg:
> >>> +          minItems: 2
> >>> +          maxItems: 2
> >
> >> This doesn't work. The main part of the schema already said there's only
> >> 1 reg region. This part is ANDed with that, not an override. You need to add an else clause with 'maxItems: 1' and change the base schema to
> >> {minItems: 1, maxItems: 2}.
> >
> > As the earlier version of base schema doesn't have "minItems: " set, should it be set to 0 for backward compatibility?  Or can it just be omitted setting in base schema as before?
>
> We've always needed at least 1 "reg" specifier in practice, so I don't
> think being backwards-compatible with broken DTs is a concern :)

'minItems: 0' would be a boolean (e.g. "reg;") and I'm not sure that's
even really valid json-schema. What you'd want here is 'reg' not
present (i.e. not in 'required').

Rob