Re: [RFC PATCH v6 3/9] dt-bindings: iommu: rockchip: allow the RK3576 NPU MMU clock set

[Jiaxing Hu <gahing@gahingwoo.com>]

Hi Diederik,

> Now every MMU with "rockchip,rk3568-iommu", "rockchip,rk3588-iommu" or
> "rockchip,rk3576-iommu" is allowed to have a minimum of 2 clocks, instead
> of having exactly 2 clocks. That does not sound desirable.

You are right, and it is worse than sounding undesirable, it actually
happens. I gave an RK3588 NPU MMU a bogus third clock and v6's schema
accepted it without a word. That is a real loss of coverage for every
existing Rockchip IOMMU and I should not have sent it that way.

Fixed for v7 the way you and the bot suggest, with a compatible of its
own:

  compatible = "rockchip,rk3576-npu-iommu", "rockchip,rk3568-iommu";

and an allOf that pins each side:

  if compatible contains rockchip,rk3576-npu-iommu
    then clocks/clock-names minItems: 5
    else clocks/clock-names maxItems: 2

so the NPU MMUs are required to carry all five and everything else is
back to exactly two. Checked in both directions: the three clock RK3588
node is rejected again, an NPU MMU with only aclk and iface is rejected,
and every rockchip dtb in the tree validates clean.

No driver change goes with it. rk_iommu matches only "rockchip,iommu"
and "rockchip,rk3568-iommu", and the fallback stays, so the new string
is documentation only.

The name is the part I am least sure of. Everything else in that binding
ends in -iommu, which is why I did not use -mmu to pair with the
rknn-core node it belongs to. Happy to change it if Heiko or Krzysztof
prefer something else.

Thanks for catching it.

Cheers,
Jiaxing