[PATCH v6 1/4] iommu/arm-smmu: add NVIDIA implementation for dual ARM MMU-500 usage

Krishna Reddy vdumpa at nvidia.com
Thu Jun 25 19:13:24 EDT 2020

>Should NVIDIA_TEGRA194_SMMU be a separate value for smmu->model, perhaps? That way we avoid this somewhat odd check here.

NVIDIA haven't made any changes to arm,mmu-500. It is only used in different topology.  New model would be mis-leading here.
As suggested by Robin, It can just be moved to end of function.

>> diff --git a/drivers/iommu/arm-smmu-nvidia.c 
>> b/drivers/iommu/arm-smmu-nvidia.c
>I wonder if it would be better to name this arm-smmu-tegra.c to make it clearer that this is for a Tegra chip. We do have regular expressions in MAINTAINERS that catch anything with "tegra" in it to make this easier.
>Also, the nsmmu_ prefix looks somewhat odd here. You already use struct nvidia_smmu as the name of the structure, so why not be consistent and continue to use nvidia_smmu_ as the prefix for function names?
>Or perhaps even use tegra_smmu_ as the prefix to match the filename change I suggested earlier.

Prefix can be updated to nvidia_smmu as we seem to be okay for now to keep file name as arm-smmu-nvidia.c after the vendor name.  

>> +#define TLB_LOOP_TIMEOUT		1000000	/* 1s! */

It is not meant for a conversion. Reused Timeout variable from arm-smmu.c for tlb_sync implementation.  Can rename it to TLB_LOOP_TIMEOUT_IN_US.

>> +	}
>> +	dev_err_ratelimited(smmu->dev,
>> +			    "TLB sync timed out -- SMMU may be deadlocked\n");
>Same here.
>Also, is there anything we can do when this happens?

This is never expected to happen on Silicon. This code and message is reused from arm-smmu.c.

>> +#define nsmmu_page(smmu, inst, page) \
>> +	(((inst) ? to_nvidia_smmu(smmu)->bases[(inst)] : smmu->base) + \
>> +	((page) << smmu->pgshift))

>Can we simply define to_nvidia_smmu(smmu)->bases[0] = smmu->base in nvidia_smmu_impl_init()? Then this would become just:
>	to_nvidia_smmu(smmu)->bases[inst] + ((page) << (smmu)->pgshift)
> +
>Maybe add this here to simplify the nsmmu_page() macro above:
>	nsmmu->bases[0] = smmu->base;

This preferred to avoid the check in nsmmu_page(). But, smmu->base is not yet populated when nvidia_smmu_impl_init() is called.  
Let me look at the alternative place to set it.


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