linux-kernel - Re: [PATCH 2/3] dt-bindings: iommu: Add NVIDIA Tegra CMDQV support

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Message-ID: <4f6496de-d3c8-4701-a9b4-6f695018eb5e@nvidia.com>
Date: Mon, 3 Nov 2025 19:24:45 +0530
From: Ashish Mhetre <amhetre@...dia.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: will@...nel.org, robin.murphy@....com, joro@...tes.org, robh@...nel.org,
 krzk+dt@...nel.org, conor+dt@...nel.org, thierry.reding@...il.com,
 jonathanh@...dia.com, jgg@...pe.ca, nicolinc@...dia.com,
 linux-tegra@...dia.com, linux-arm-kernel@...ts.infradead.org,
 iommu@...ts.linux.dev, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org
Subject: Re: [PATCH 2/3] dt-bindings: iommu: Add NVIDIA Tegra CMDQV support


On 10/31/2025 1:44 PM, Krzysztof Kozlowski wrote:
> External email: Use caution opening links or attachments
>
>
> On Fri, Oct 31, 2025 at 06:29:58AM +0000, Ashish Mhetre wrote:
>> The Command Queue Virtualization (CMDQV) hardware is part of the
>> SMMUv3 implementation on NVIDIA Tegra SoCs. 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?
>> 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 <amhetre@...dia.com>
>> ---
>>   .../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 <linux-tegra@...dia.com>
> 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 <dt-bindings/interrupt-controller/arm-gic.h>
>> +    #include <dt-bindings/interrupt-controller/irq.h>
>> +
>> +    cmdqv: cmdqv@...5200000 {
> Drop unused label

Okay, I will remove the label.
> Best regards,
> Krzysztof
>