Re: [PATCH v6 2/9] dt-bindings: media: nxp: Add Wave6 video codec device

[Krzysztof Kozlowski]

On Thu, Jun 25, 2026 at 01:43:33AM +0000, Nas Chung wrote:
> >> +  sram:
> >> +    $ref: /schemas/types.yaml#/definitions/phandle
> >> +    description:
> >> +      phandle to the SRAM node used to store reference data, reducing DMA
> >> +      memory bandwidth.
> >> +
> >> +  iommus:
> >> +    maxItems: 1
> >> +
> >> +  "#cooling-cells":
> >> +    const: 2
> >> +
> >> +  "#address-cells":
> >> +    const: 2
> >> +
> >> +  "#size-cells":
> >> +    const: 2
> >> +
> >> +  ranges: true
> >> +
> >> +patternProperties:
> >> +  "^interface@[0-9a-f]+$":
> >
> >I have to wonder if this interface business is required at all.
> >Why can this not go into the parent, with each region fetchable via
> >reg-names, interrupt-names and iommu-names?
> 
> Thanks for your feedback.
> 
> I did try the flat model, but the blocker is the IOMMU.
> 
> The control region and four interface regions are independent DMA requesters
> with distinct stream IDs, and each interface can be assigned to a different VM,
> driving the video core with its own isolated memory.
> 
> If all stream IDs are listed under the parent's iommus, they bind to a
> single device and share one domain, so the isolation is lost.
> This is the main reason I added the interface nodes.

Feels similar to issue Qualcomm has. I rejected such subnodes and
Qualcomm came with a solution in DMA IOMMU code, but that solution was
rejected by DMA folks:
https://lore.kernel.org/all/c7b956a9-d3e8-4e18-b780-5d08f5cd2ca1@xxxxxxxxxx/

I don't have proper arguments to convince DMA folks, thus I agree for
Qualcomm for the subnodes. It should be fine here as well, in such case.

Best regards,
Krzysztof