Re: [PATCH 3/6] dt-bindings: iommu: Add Broadcom BCM2712 IOMMU

[Krzysztof Kozlowski]

On Sun, Jul 12, 2026 at 10:18:53PM +0100, Daniel Drake wrote:
> Add bindings for the Broadcom BCM2712 IOMMU and its shared TLB cache.
> 
> Include compatibility with the cache phandle used in existing firmware
> shipped on Raspberry Pi 5, and also allow the iova-window to be omitted,
> which similarly will maintain compatibility with existing RPi5 firmware.
> 
> Signed-off-by: Daniel Drake <dan@xxxxxxxxxxxxxxx>
> ---
>  .../bindings/iommu/brcm,bcm2712-iommu.yaml         | 65 ++++++++++++++++++++++
>  .../bindings/iommu/brcm,bcm2712-iommuc.yaml        | 35 ++++++++++++
>  2 files changed, 100 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/iommu/brcm,bcm2712-iommu.yaml b/Documentation/devicetree/bindings/iommu/brcm,bcm2712-iommu.yaml
> new file mode 100644
> index 000000000000..0d91c513afc4
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iommu/brcm,bcm2712-iommu.yaml
> @@ -0,0 +1,65 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/iommu/brcm,bcm2712-iommu.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Broadcom BCM2712 IOMMU
> +
> +maintainers:
> +  - Daniel Drake <dan@xxxxxxxxxxxxxxx>
> +
> +description: |

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

> +  The BCM2712 IOMMU provides address translation for various hardware blocks
> +  on the BCM2712 SoC, such as the VC6 display pipeline.
> +
> +properties:
> +  compatible:
> +    const: brcm,bcm2712-iommu
> +
> +  reg:
> +    maxItems: 1
> +
> +  '#iommu-cells':
> +    const: 0
> +
> +  brcm,iommu-cache:
> +    $ref: /schemas/types.yaml#/definitions/phandle
> +    description: Phandle to the shared IOMMU cache (IOMMUC).

You need to explain what for, the purpose in hardware.

> +
> +  cache:
> +    $ref: /schemas/types.yaml#/definitions/phandle
> +    description: Deprecated. Use brcm,iommu-cache instead.
> +    deprecated: true

Drop property, we do not take new bindings with deprecated properties.
Existing FW is not an excuse, Raspberry 5 developers could reach out and
ask if this is okay. They did not.

> +
> +  brcm,iova-window:
> +    $ref: /schemas/types.yaml#/definitions/uint64-array
> +    description: |
> +      An array of two 64-bit integers specifying the IOVA aperture start
> +      address and the aperture size. IOMMU mappings will be created inside
> +      this aperture. All preceding address space is in identity/bypass mode.
> +      The aperture start address must be 4GB-aligned.
> +      Should be considered a required property, but it is technically optional
> +      in order to maintain compatibility with historical firmware versions.
> +      If absent, defaults to a 4GB window at 40GiB (0xa00000000).
> +    items:
> +      - description: IOVA window start address
> +      - description: IOVA window size

This looks a lot like reserved region, so why do you need a new
property? If this is not a reserved memory, then why compatible does not
imply the value?


> +
> +required:
> +  - compatible
> +  - reg
> +  - '#iommu-cells'
> +  - brcm,iommu-cache
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    iommu@5200 {
> +        compatible = "brcm,bcm2712-iommu";
> +        reg = <0x5200 0x80>;
> +        brcm,iommu-cache = <&iommuc>;
> +        #iommu-cells = <0>;
> +        brcm,iova-window = /bits/ 64 <0xa00000000 0x100000000>;

Best regards,
Krzysztof