linux-kernel - Re: [PATCH v2 1/8] dt-bindings: arm-smmu: Add Adreno GPU variant

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Message-ID: <3a283a7c-df75-a30a-1bcb-74e631f06a71@arm.com>
Date:   Wed, 4 Dec 2019 15:55:57 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Jordan Crouse <jcrouse@...eaurora.org>,
        iommu@...ts.linux-foundation.org
Cc:     will@...nel.org, linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH v2 1/8] dt-bindings: arm-smmu: Add Adreno GPU variant

On 22/11/2019 11:31 pm, Jordan Crouse wrote:
> Add a compatible string to identify SMMUs that are attached
> to Adreno GPU devices that wish to support split pagetables.

A software policy decision is not, in itself, a good justification for a 
DT property. Is the GPU SMMU fundamentally different in hardware* from 
the other SMMU(s) in any given SoC?

(* where "hardware" may encompass hypervisor shenanigans)

> Signed-off-by: Jordan Crouse <jcrouse@...eaurora.org>
> ---
> 
>   Documentation/devicetree/bindings/iommu/arm,smmu.yaml | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/iommu/arm,smmu.yaml b/Documentation/devicetree/bindings/iommu/arm,smmu.yaml
> index 6515dbe..db9f826 100644
> --- a/Documentation/devicetree/bindings/iommu/arm,smmu.yaml
> +++ b/Documentation/devicetree/bindings/iommu/arm,smmu.yaml
> @@ -31,6 +31,12 @@ properties:
>                 - qcom,sdm845-smmu-v2
>             - const: qcom,smmu-v2
>   
> +      - description: Qcom Adreno GPU SMMU iplementing split pagetables
> +        items:
> +          - enum:
> +              - qcom,adreno-smmu-v2
> +          - const: qcom,smmu-v2

Given that we already have per-SoC compatibles for Qcom SMMUs in 
general, this seems suspiciously vague.

Robin.

> +
>         - description: Qcom SoCs implementing "arm,mmu-500"
>           items:
>             - enum:
>