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

On Wed, Aug 19, 2020 at 10:36:38AM -0700, Rob Clark wrote:

On Wed, Aug 19, 2020 at 10:03 AM Doug Anderson [off-list ref] wrote:

quoted

Hi,

On Mon, Aug 17, 2020 at 3:03 PM Rob Clark [off-list ref] wrote:

quoted

From: Jordan Crouse <redacted>

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 <redacted>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Rob Clark <redacted>
---
 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 (local)

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...

I did bring up the thing about removing the compat string in an
earlier revision of the series.. but then we realized that
qcom,sc7180-smmu-v2 was never actually used anywhere.

But I guess we could:  compatible = "qcom,sc7180-smmu-v2",
"qcom,adreno-smmu", "qcom,smmu-v2";

I think the SoC specific string is intended for the "other" SMMU that everybody
else uses. Rarely would a workaround for that SMMU affect the GPU and vice
versa. Since these are the bindings it doesn't hurt to allow for the possibility
but I would be surprised if the occasion presented itself.

Jordan

BR,
-R

quoted

-Doug

quoted

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

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