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

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Message-ID: <BYAPR12MB2822B1D5791811EDAF35C5B2B3920@BYAPR12MB2822.namprd12.prod.outlook.com>
Date:   Thu, 25 Jun 2020 23:13:24 +0000
From:   Krishna Reddy <vdumpa@...dia.com>
To:     Thierry Reding <thierry.reding@...il.com>
CC:     Sachin Nikam <Snikam@...dia.com>,
        Mikko Perttunen <mperttunen@...dia.com>,
        Bryan Huntsman <bhuntsman@...dia.com>,
        "will@...nel.org" <will@...nel.org>,
        "joro@...tes.org" <joro@...tes.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Pritesh Raithatha <praithatha@...dia.com>,
        Timo Alho <talho@...dia.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        Nicolin Chen <nicolinc@...dia.com>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        Yu-Huan Hsu <YHsu@...dia.com>,
        Thierry Reding <treding@...dia.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Bitan Biswas <bbiswas@...dia.com>
Subject: RE: [PATCH v6 1/4] iommu/arm-smmu: add NVIDIA implementation for dual
 ARM MMU-500 usage

>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! */
>USEC_PER_SEC?

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.

-KR