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

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Date:   Wed, 4 Dec 2019 10:01:42 -0800
From:   Rob Clark <robdclark@...il.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Jordan Crouse <jcrouse@...eaurora.org>,
        "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <iommu@...ts.linux-foundation.org>,
        Mark Rutland <mark.rutland@....com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Will Deacon <will@...nel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 1/8] dt-bindings: arm-smmu: Add Adreno GPU variant

On Wed, Dec 4, 2019 at 7:56 AM Robin Murphy <robin.murphy@....com> wrote:
>
> 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?

The GPU CP has some sort of mechanism to switch pagetables.. although
I guess under the firmware it is all the same.  Jordan should know
better..

BR,
-R

> (* 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:
> >
> _______________________________________________
> iommu mailing list
> iommu@...ts.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/iommu

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