On 2020-07-01 20:39, Krishna Reddy wrote:
On 01/07/2020 20:00, Krishna Reddy wrote:
+        items:
+          - enum:
+              - nvdia,tegra194-smmu
+          - const: arm,mmu-500

Is the fallback compatible appropriate here? If software treats this as a 
standard MMU-500 it will only program the first instance (because the second 
isn't presented as a separate MMU-500) - is there any way that isn't going to 
blow up?

When compatible is set to both nvidia,tegra194-smmu and arm,mmu-500, 
implementation override ensure that both instances are programmed. Isn't it? I 
am not sure I follow your comment fully.

The problem is, if for some reason someone had a Tegra194, but only set the compatible 
string to 'arm,mmu-500' it would assume that it was a normal arm,mmu-500 and only one 
instance would be programmed. We always want at least 2 of the 3 instances 
>>programmed and so we should only match 'nvidia,tegra194-smmu'. In fact, I think 
that we also need to update the arm_smmu_of_match table to add 'nvidia,tegra194-smmu' 
with the data set to &arm_mmu500.

In that case, new binding "nvidia,smmu-v2" can be added with data set to 
&arm_mmu500 and enumeration would have nvidia,tegra194-smmu and another variant for next 
generation SoC in future.

I think you would be better off with nvidia,smmu-500 as smmu-v2 appears to be 
something different. I see others have a smmu-v2 but I am not sure if that is 
legacy. We have an smmu-500 and so that would seem more appropriate.

I tried to use the binding synonymous to other vendors.
V2 is the architecture version.  MMU-500 is the actual implementation from ARM 
based on V2 arch.  As we just use the MMU-500 IP as it is, It can be named as 
nvidia,smmu-500 or similar as well.

Yup, that sounds OK to me if you want a broader compatible to potentially match other future SoCs as well.

Others probably having their own implementation based on V2 arch.

Exactly - "cavium,smmu-v2" and "qcom,smmu-v2" are their own in-house microarchitectures, not one of Arm's designs, so they don't really have a suitable 'product name' we could have used for the bindings.

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