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

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Message-ID: <20251031-witty-sociable-chachalaca-b73dbc@kuoka>
Date: Fri, 31 Oct 2025 09:14:25 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Ashish Mhetre <amhetre@...dia.com>
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 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.

> 
> 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

> +description: |

Do not need '|' unless you need to preserve formatting.

> +  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.

> +
> +properties:
> +  compatible:
> +    const: nvidia,tegra264-cmdqv
> +
> +  reg:
> +    maxItems: 1
> +
> +  interrupts:
> +    maxItems: 1
> +
> +  interrupt-names:
> +    items:
> +      - const: cmdqv

Drop interript names, obvious.

> +
> +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

Best regards,
Krzysztof