Re: [PATCH v2 1/9] dt-bindings: dma: nvidia,tegra186-gpc-dma: Add iommu-map property

Jon Hunter
2026-03-10T09:47:58Z

On 10/03/2026 04:44, Akhil R wrote:

...

> Looking at the qcom,sm8750-camss.yaml, each iommus entry is describing a
> functionally distinct hardware block like IPE, JPEG, etc. Here for
> GPCDMA the channels and the stream IDs are identical in hardware and there
> is nothing functionally unique about any individual channel to describe.
>
> If the channels and stream IDs are consecutive, as Frank mentioned in
> the previous version, we would need only one iommu-map entry for all
> the channels. In a virtualized system the hypervisor may assign
> non-consecutive stream IDs, or a scattered channel mask. That would
> require multiple entries.
>
> I will document this in the description. Please let me know if it sounds
> good or if you have any suggestions.

Even in the non-virtualised case we can set dma-channel-mask property
and only enable specific channels. Given that the hardware allows this
flexibility and we could potentially have various different
permutations. So I think that we need to have a flexible number of items
for iommu-map. And yes, let's describe that clearer in the commit message.

Jon

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nvpublic