RE: [PATCH v8 1/3] iommu/arm-smmu: add NVIDIA implementation for dual ARM MMU-500 usage

[Krishna Reddy]

>> The driver intend to support up to 3 instances. It doesn't really mandate that all three instances be present in same DT node.
>> Each mmio aperture in "reg" property is an instance here. reg = 
>> <inst0_base, size>, <inst1_base, size>, <inst2_base, size>; The reg can have all three or less and driver just configures based on reg and it works fine.

>So it sounds like we need at least 2 SMMUs (for non-iso and iso) but we have up to 3 (for Tegra194). So the question is do we have a use-case where we only use 2 and not 3? If not, then it still seems that we should require that all 3 are present.

It can be either 2 SMMUs (for non-iso) or 3 SMMUs (for non-iso and iso).  Let me fail the one instance case as it can use regular arm smmu implementation and don't  need nvidia implementation explicitly.
 
>The other problem I see here is that currently the arm-smmu binding defines the 'reg' with a 'maxItems' of 1, whereas we have 3. I believe that this will get caught by the 'dt_binding_check' when we try to populate the binding.

Thanks for pointing it out! Will update the binding doc.

-KR

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nvpublic