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: <e6da9661-4e62-6e34-ac21-63ff993ca8bc@nvidia.com>
Date:   Tue, 30 Jun 2020 11:17:38 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Krishna Reddy <vdumpa@...dia.com>
CC:     <joro@...tes.org>, <will@...nel.org>, <robin.murphy@....com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <iommu@...ts.linux-foundation.org>, <linux-kernel@...r.kernel.org>,
        <linux-tegra@...r.kernel.org>, <treding@...dia.com>,
        <yhsu@...dia.com>, <snikam@...dia.com>, <praithatha@...dia.com>,
        <talho@...dia.com>, <bbiswas@...dia.com>, <mperttunen@...dia.com>,
        <nicolinc@...dia.com>, <bhuntsman@...dia.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 01:10, Krishna Reddy wrote:
> NVIDIA's Tegra194 SoC uses two ARM MMU-500s together to interleave
> IOVA accesses across them.
> Add NVIDIA implementation for dual ARM MMU-500s and add new compatible
> string for Tegra194 SoC SMMU topology.
> 
> Signed-off-by: Krishna Reddy <vdumpa@...dia.com>
> ---
>  MAINTAINERS                     |   2 +
>  drivers/iommu/Makefile          |   2 +-
>  drivers/iommu/arm-smmu-impl.c   |   3 +
>  drivers/iommu/arm-smmu-nvidia.c | 196 ++++++++++++++++++++++++++++++++
>  drivers/iommu/arm-smmu.h        |   1 +
>  5 files changed, 203 insertions(+), 1 deletion(-)
>  create mode 100644 drivers/iommu/arm-smmu-nvidia.c

...

> +struct arm_smmu_device *nvidia_smmu_impl_init(struct arm_smmu_device *smmu)
> +{
> +	unsigned int i;
> +	struct nvidia_smmu *nvidia_smmu;
> +	struct platform_device *pdev = to_platform_device(smmu->dev);
> +
> +	nvidia_smmu = devm_kzalloc(smmu->dev, sizeof(*nvidia_smmu), GFP_KERNEL);
> +	if (!nvidia_smmu)
> +		return ERR_PTR(-ENOMEM);
> +
> +	nvidia_smmu->smmu = *smmu;
> +	/* Instance 0 is ioremapped by arm-smmu.c after this function returns */
> +	nvidia_smmu->num_inst = 1;
> +
> +	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.
In the future if there is an SoC that has less (hopefully not more) than
Tegra194 then we should handle this via the DT compatible string. In
other words, we should always know how many SMMUs there are for a given
SoC and how many we should initialise.

> +
> +		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.

Jon

-- 
nvpublic