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

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Message-ID: <BYAPR12MB282290F6E270DB90040379A0B36F0@BYAPR12MB2822.namprd12.prod.outlook.com>
Date:   Tue, 30 Jun 2020 20:21:44 +0000
From:   Krishna Reddy <vdumpa@...dia.com>
To:     Jonathan Hunter <jonathanh@...dia.com>
CC:     "joro@...tes.org" <joro@...tes.org>,
        "will@...nel.org" <will@...nel.org>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        Thierry Reding <treding@...dia.com>,
        "Yu-Huan Hsu" <YHsu@...dia.com>, Sachin Nikam <Snikam@...dia.com>,
        Pritesh Raithatha <praithatha@...dia.com>,
        Timo Alho <talho@...dia.com>,
        Bitan Biswas <bbiswas@...dia.com>,
        Mikko Perttunen <mperttunen@...dia.com>,
        Nicolin Chen <nicolinc@...dia.com>,
        Bryan Huntsman <bhuntsman@...dia.com>,
        "nicoleotsuka@...il.com" <nicoleotsuka@...il.com>
Subject: RE: [PATCH v8 1/3] iommu/arm-smmu: add NVIDIA implementation for dual
 ARM MMU-500 usage

>> 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

--
nvpublic