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

From: Rob Clark <robdclark@gmail.com>
To: Robin Murphy <robin.murphy@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
	<devicetree@vger.kernel.org>,
	linux-arm-msm <linux-arm-msm@vger.kernel.org>,
	"list@263.net:IOMMU DRIVERS <iommu@lists.linux-foundation.org>,
	Joerg Roedel <joro@8bytes.org>,
	" <iommu@lists.linux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Rob Herring <robh+dt@kernel.org>, Will Deacon <will@kernel.org>,
	"moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE"
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v2 1/8] dt-bindings: arm-smmu: Add Adreno GPU variant
Date: Wed, 4 Dec 2019 10:01:42 -0800	[thread overview]
Message-ID: <CAF6AEGuxgUQNuSQVECiUzpj4DM0R7UYme0Q9ggF1a=JCxAJsBA@mail.gmail.com> (raw)
In-Reply-To: <3a283a7c-df75-a30a-1bcb-74e631f06a71@arm.com>

On Wed, Dec 4, 2019 at 7:56 AM Robin Murphy <robin.murphy@arm.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@codeaurora.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:
> >
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