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

On 10/31/2025 1:44 PM, Krzysztof Kozlowski wrote:

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On Fri, Oct 31, 2025 at 06:29:58AM +0000, Ashish Mhetre wrote:

quoted

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?

quoted

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 <redacted>
---
  .../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.

quoted

+description: |

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

Okay, I'll remove this in next version.

quoted

+  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 [off-list ref]

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.

quoted

+
+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.

quoted

+
+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