linux-kernel - Re: [PATCH 10/20] dt-bindings: arm-smmu: Add compatible string for Adreno GPU SMMU

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Message-ID: <CAD=FV=VzYSL-3q0oFPPSP7FiEdLeTEN6Zy=kp-73B=8LAavmVw@mail.gmail.com>
Date:   Wed, 19 Aug 2020 10:02:20 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Rob Clark <robdclark@...il.com>
Cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <iommu@...ts.linux-foundation.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        Will Deacon <will@...nel.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Sibi Sankar <sibis@...eaurora.org>,
        Vivek Gautam <vivek.gautam@...eaurora.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        Jordan Crouse <jcrouse@...eaurora.org>,
        Rob Herring <robh@...nel.org>,
        Rob Clark <robdclark@...omium.org>,
        Rob Herring <robh+dt@...nel.org>,
        "moderated list:ARM SMMU DRIVERS" 
        <linux-arm-kernel@...ts.infradead.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 10/20] dt-bindings: arm-smmu: Add compatible string for
 Adreno GPU SMMU

Hi,

On Mon, Aug 17, 2020 at 3:03 PM Rob Clark <robdclark@...il.com> wrote:
>
> From: Jordan Crouse <jcrouse@...eaurora.org>
>
> Every Qcom Adreno GPU has an embedded SMMU for its own use. These
> devices depend on unique features such as split pagetables,
> different stall/halt requirements and other settings. Identify them
> with a compatible string so that they can be identified in the
> arm-smmu implementation specific code.
>
> Signed-off-by: Jordan Crouse <jcrouse@...eaurora.org>
> Reviewed-by: Rob Herring <robh@...nel.org>
> Signed-off-by: Rob Clark <robdclark@...omium.org>
> ---
>  Documentation/devicetree/bindings/iommu/arm,smmu.yaml | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/iommu/arm,smmu.yaml b/Documentation/devicetree/bindings/iommu/arm,smmu.yaml
> index 503160a7b9a0..5ec5d0d691f6 100644
> --- a/Documentation/devicetree/bindings/iommu/arm,smmu.yaml
> +++ b/Documentation/devicetree/bindings/iommu/arm,smmu.yaml
> @@ -40,6 +40,10 @@ properties:
>                - qcom,sm8150-smmu-500
>                - qcom,sm8250-smmu-500
>            - const: arm,mmu-500
> +      - description: Qcom Adreno GPUs implementing "arm,smmu-v2"
> +        items:
> +          - const: qcom,adreno-smmu
> +          - const: qcom,smmu-v2

I know I'm kinda late to the game, but this seems weird to me,
especially given the later patches in the series like:

https://lore.kernel.org/r/20200817220238.603465-19-robdclark@gmail.com

Specifically in that patch you can see that this IOMMU already had a
compatible string and we're changing it and throwing away the
model-specific string?  I'm guessing that you're just trying to make
it easier for code to identify the adreno iommu, but it seems like a
better way would have been to just add the adreno compatible in the
middle, like:

      - description: Qcom Adreno GPUs implementing "arm,smmu-v2"
        items:
          - enum:
              - qcom,msm8996-smmu-v2
              - qcom,msm8998-smmu-v2
              - qcom,sc7180-smmu-v2
              - qcom,sdm845-smmu-v2
        - const: qcom,adreno-smmu
        - const: qcom,smmu-v2

Then we still have the SoC-specific compatible string in case we need
it but we also have the generic one?  It also means that we're not
deleting the old compatible string...

-Doug


>        - description: Marvell SoCs implementing "arm,mmu-500"
>          items:
>            - const: marvell,ap806-smmu-500
> --
> 2.26.2
>