linux-kernel - Re: [PATCH v10 4/5] dt-bindings: arm-smmu: add binding for Tegra194 SMMU

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Message-ID: <c2ab2a0d-419d-555f-c124-2cfa1ecb2a81@arm.com>
Date:   Mon, 13 Jul 2020 15:10:25 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Krishna Reddy <vdumpa@...dia.com>, Rob Herring <robh@...nel.org>
Cc:     "joro@...tes.org" <joro@...tes.org>,
        "will@...nel.org" <will@...nel.org>,
        Thierry Reding <treding@...dia.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        Yu-Huan Hsu <YHsu@...dia.com>,
        Sachin Nikam <Snikam@...dia.com>,
        Pritesh Raithatha <praithatha@...dia.com>,
        Timo Alho <talho@...dia.com>,
        Bitan Biswas <bbiswas@...dia.com>,
        Mikko Perttunen <mperttunen@...dia.com>,
        Nicolin Chen <nicolinc@...dia.com>,
        Bryan Huntsman <bhuntsman@...dia.com>,
        "nicoleotsuka@...il.com" <nicoleotsuka@...il.com>
Subject: Re: [PATCH v10 4/5] dt-bindings: arm-smmu: add binding for Tegra194
 SMMU

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 :)

Robin.

> 
> "else" part to set "maxItems: 1" and setting "maxItems: 2" in base schema is clear to me.
> 
> 
> -KR
>