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Tue, 30 Jun 2020 16:44:25 +0000 Subject: Re: [PATCH v8 1/3] iommu/arm-smmu: add NVIDIA implementation for dual ARM MMU-500 usage From: Jon Hunter To: Krishna Reddy References: <20200630001051.12350-1-vdumpa@nvidia.com> <20200630001051.12350-2-vdumpa@nvidia.com> <4037efc7-fbed-e8cf-dac7-212c65014e4e@nvidia.com> Message-ID: Date: Tue, 30 Jun 2020 17:44:23 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <4037efc7-fbed-e8cf-dac7-212c65014e4e@nvidia.com> X-Originating-IP: [10.124.1.5] X-ClientProxiedBy: HQMAIL111.nvidia.com (172.20.187.18) To HQMAIL107.nvidia.com (172.20.187.13) Content-Language: en-US DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1593535420; bh=wfS2EeHQkmlhZY5U4/UFUr69ArCFndTN9ROhcFPEI1M=; h=X-PGP-Universal:Subject:From:To:CC:References:Message-ID:Date: User-Agent:MIME-Version:In-Reply-To:X-Originating-IP: X-ClientProxiedBy:Content-Type:Content-Language: Content-Transfer-Encoding; b=RpzzfzIx5Pvr8kBRvnnxiXZncwQ9u01wYvBZU7qtc0WldUlzAiBfBsBypPux7uaZ7 Mq2kKQhObMQz4+2w6EMvtTBA2Ze5CTHbAPKzP1ViLUXqbGrxMWtiCASh0ZReWsE5Ml KQJdovzVUgyfbtAeQd4TtYuX+9pIP9FMdQcRi1nuCwpLbEIzI583GI2XPALg8/8drf zGPquwH0ymfoL/FVTw2J3LhGOh+oMmQ2OGDookibXrLDT6YEKcRBUVw+lhkyqeGSto KkUNRaHAYsNB+kcYkssfiGLkwASZSzb9ID3DyV+xlku+sYrTx0K5DXc+wjxbrnqIP5 iaVGNwznKEgSw== Cc: Sachin Nikam , "nicoleotsuka@gmail.com" , Mikko Perttunen , Bryan Huntsman , "will@kernel.org" , "linux-kernel@vger.kernel.org" , Pritesh Raithatha , Timo Alho , "iommu@lists.linux-foundation.org" , Nicolin Chen , "linux-tegra@vger.kernel.org" , Yu-Huan Hsu , Thierry Reding , "robin.murphy@arm.com" , "linux-arm-kernel@lists.infradead.org" , Bitan Biswas X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On 30/06/2020 17:32, Jon Hunter wrote: > On 30/06/2020 17:23, Krishna Reddy wrote: >>>> +struct arm_smmu_device *nvidia_smmu_impl_init(struct arm_smmu_device >>>> +*smmu) { >>>> + unsigned int i; >> .... >>>> + for (i = 1; i < MAX_SMMU_INSTANCES; i++) { >>>> + struct resource *res; >>>> + >>>> + res = platform_get_resource(pdev, IORESOURCE_MEM, i); >>>> + if (!res) >>>> + break; >> >>> Currently this driver is only supported for Tegra194 which I understand has 3 SMMUs. Therefore, I don't feel that we should fail silently here, I think it is better to return an error if all 3 cannot be initialised. >> >> Initialization of all the three SMMU instances is not necessary here. > > That is not what I am saying. > >> The driver can work with all the possible number of instances 1, 2 and 3 based on the DT config though it doesn't make much sense to use it with 1 instance. >> There is no silent failure here from driver point of view. If there is misconfig in DT, SMMU faults would catch issues. > > I disagree and you should return a proper error here. OK, well I see what you are saying, but if we intended to support all 3 for Tegra194, then we should ensure all 3 are initialised correctly. My concern here is testing, because when things break in upstream I am usually the one that tracks it down. Not having clear warning/error messages when something is not initialised as expected makes it harder. It would be better to query the number of SMMUs populated in device-tree and then ensure that all are initialised correctly. Jon -- nvpublic _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu