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: <4037efc7-fbed-e8cf-dac7-212c65014e4e@nvidia.com>
Date:   Tue, 30 Jun 2020 17:32:41 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Krishna Reddy <vdumpa@...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



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.

>>> +		nvidia_smmu->bases[i] = devm_ioremap_resource(smmu->dev, res);
>>> +		if (IS_ERR(nvidia_smmu->bases[i]))
>>> +			return ERR_CAST(nvidia_smmu->bases[i]);
> 
>> You want to use PTR_ERR() here.
> 
> PTR_ERR() returns long integer. 
> This function returns a pointer. ERR_CAST is the right one to use here. 

Ah yes, indeed. OK that's fine.

Jon

-- 
nvpublic