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

[Ashish Mhetre]

On 11/3/2025 7:24 PM, Ashish Mhetre wrote:
> 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?

Hi Krzysztof, Thierry,
Any suggestions on this?

> > > 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@xxxxxxxxxx>
> > > ---
> > >   .../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@xxxxxxxxxx>
> > 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@8105200000 {
> > Drop unused label
>
> Okay, I will remove the label.
> > Best regards,
> > Krzysztof