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It assists in >>>>> virtualizing the command queue for the SMMU. >>>> If this is specific to Nvidia, then I think you need specific front >>>> compatible and disallow it for other vendors. >>> >>> Yes, CMDQV is specific to Nvidia. There isn't currently a >>> vendor-specific >>> compatible for Nvidia's arm,smmu-v3 implementation. Would it be >>> acceptable >>> to document this as Nvidia-specific in the description? Or can we add a >>> new Nvidia-specific compatible string like "nvidia,smmu-v3" if that's >>> preferred and use conditional schema to restrict the property? >> >> Hi Will, Robin, >> >> Do you have any suggestions on this? I have followed existing ACPI >> approach >> for implementing DT support. > > No, the way the ACPI binding is implemented has the lookup going *from* > the CMDQV node back to the SMMU instance (via the matching identifier) - > this is entirely the opposite. The literal DT equivalent would be to use > for_each_matching_node/for_each_compatible_node to scan the CMDQV nodes > for a property indicating the relevant SMMU. > > I'm not hugely fussed either way though - since the fact is the Tegra234 > SMMU does have this custom modification, a specific > "nvidia,tegra234-smmu", "arm,smmu-v3" compatible isn't inappropriate, > even if it really doesn't make any difference to architectural SMMU > operation without awareness of the other CMDQV nodes. > > Thanks, > Robin. > Thanks for the suggestions Robin. Approach 2 is much simpler with current implementation I have. I will proceed with adding Nvidia specific compatible string "nvidia,tegra264-smmu", "arm,smmu-v3" in V2. >> Will it be fine to add separate compatible >> string >> for Nvidia Tegra264 SMMU to restrict the usage of CMDQV? >> >>>>> Add a new device tree binding document for nvidia,tegra264-cmdqv. >>>>> >>>>> Also update the arm,smmu-v3 binding to include an optional >>>>> nvidia,cmdqv >>>>> property. This property is a phandle to the CMDQV device node, >>>>> allowing >>>>> the SMMU driver to associate with its corresponding CMDQV instance. >>>>> >>>>> Signed-off-by: Ashish Mhetre >>>>> --- >>>>>   .../bindings/iommu/arm,smmu-v3.yaml           | 10 ++++ >>>>>   .../bindings/iommu/nvidia,tegra264-cmdqv.yaml | 46 +++++++++++++++ >>>>> ++++ >>>>>   2 files changed, 56 insertions(+) >>>>>   create mode 100644 Documentation/devicetree/bindings/iommu/ >>>>> nvidia,tegra264-cmdqv.yaml >>>>> >>>>> diff --git a/Documentation/devicetree/bindings/iommu/arm,smmu- >>>>> v3.yaml b/Documentation/devicetree/bindings/iommu/arm,smmu-v3.yaml >>>>> index 75fcf4cb52d9..edc0c20a0c80 100644 >>>>> --- a/Documentation/devicetree/bindings/iommu/arm,smmu-v3.yaml >>>>> +++ b/Documentation/devicetree/bindings/iommu/arm,smmu-v3.yaml >>>>> @@ -58,6 +58,15 @@ properties: >>>>> >>>>>     msi-parent: true >>>>> >>>>> +  nvidia,cmdqv: >>>>> +    description: | >>>>> +      A phandle to its pairing CMDQV extension for an >>>>> implementation on NVIDIA >>>>> +      Tegra SoC. >>>>> + >>>>> +      If this property is absent, CMDQ-Virtualization won't be used >>>>> and SMMU >>>>> +      will only use its own CMDQ. >>>>> +    $ref: /schemas/types.yaml#/definitions/phandle >>>>> + >>>>>     hisilicon,broken-prefetch-cmd: >>>>>       type: boolean >>>>>       description: Avoid sending CMD_PREFETCH_* commands to the SMMU. >>>>> @@ -92,4 +101,5 @@ examples: >>>>>               dma-coherent; >>>>>               #iommu-cells = <1>; >>>>>               msi-parent = <&its 0xff0000>; >>>>> +            nvidia,cmdqv = <&cmdqv>; >>>>>       }; >>>>> diff --git a/Documentation/devicetree/bindings/iommu/ >>>>> nvidia,tegra264-cmdqv.yaml b/Documentation/devicetree/bindings/ >>>>> iommu/nvidia,tegra264-cmdqv.yaml >>>>> new file mode 100644 >>>>> index 000000000000..f22c370278a3 >>>>> --- /dev/null >>>>> +++ b/Documentation/devicetree/bindings/iommu/nvidia,tegra264- >>>>> cmdqv.yaml >>>>> @@ -0,0 +1,46 @@ >>>>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) >>>>> +%YAML 1.2 >>>>> +--- >>>>> +$schema: http://devicetree.org/meta-schemas/core.yaml# >>>>> + >>>>> +title: NVIDIA Tegra264 CMDQV >>>> Missing blank line >>> >>> Ack, I will correct this in V2. >>>>> +description: | >>>> Do not need '|' unless you need to preserve formatting. >>> >>> Okay, I'll remove this in next version. >>>>> +  The CMDQ-Virtualization hardware block is part of the SMMUv3 >>>>> implementation >>>>> +  on Tegra264 SoCs. It assists in virtualizing the command queue >>>>> for the SMMU. >>>>> + >>>>> +maintainers: >>>>> +  - NVIDIA Corporation >>>> No. It should be a person. If entire Nvidia cannot find a person, I >>>> don't think we are interested in having this in the kernel. >>> >>> Okay, I'll add Nicolin as maintainer. >>>>> + >>>>> +properties: >>>>> +  compatible: >>>>> +    const: nvidia,tegra264-cmdqv >>>>> + >>>>> +  reg: >>>>> +    maxItems: 1 >>>>> + >>>>> +  interrupts: >>>>> +    maxItems: 1 >>>>> + >>>>> +  interrupt-names: >>>>> +    items: >>>>> +      - const: cmdqv >>>> Drop interript names, obvious. >>> >>> Sure, I will update in V2. >>>>> + >>>>> +required: >>>>> +  - compatible >>>>> +  - reg >>>>> +  - interrupts >>>>> +  - interrupt-names >>>>> + >>>>> +additionalProperties: false >>>>> + >>>>> +examples: >>>>> +  - | >>>>> +    #include >>>>> +    #include >>>>> + >>>>> +    cmdqv: cmdqv@8105200000 { >>>> Drop unused label >>> >>> Okay, I will remove the label. >>>> Best regards, >>>> Krzysztof >>>>