linux-kernel - Re: [PATCH v6 20/25] iommu/arm-smmu-v3-iommufd: Add hw_info to impl

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Message-ID: <20250619185325.GB17127@nvidia.com>
Date: Thu, 19 Jun 2025 15:53:25 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Pranjal Shrivastava <praan@...gle.com>
Cc: Nicolin Chen <nicolinc@...dia.com>, kevin.tian@...el.com,
	corbet@....net, will@...nel.org, bagasdotme@...il.com,
	robin.murphy@....com, joro@...tes.org, thierry.reding@...il.com,
	vdumpa@...dia.com, jonathanh@...dia.com, shuah@...nel.org,
	jsnitsel@...hat.com, nathan@...nel.org, peterz@...radead.org,
	yi.l.liu@...el.com, mshavit@...gle.com, zhangzekun11@...wei.com,
	iommu@...ts.linux.dev, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-tegra@...r.kernel.org, linux-kselftest@...r.kernel.org,
	patches@...ts.linux.dev, mochs@...dia.com, alok.a.tiwari@...cle.com,
	vasant.hegde@....com, dwmw2@...radead.org, baolu.lu@...ux.intel.com
Subject: Re: [PATCH v6 20/25] iommu/arm-smmu-v3-iommufd: Add hw_info to
 impl_ops

On Thu, Jun 19, 2025 at 11:47:24AM +0000, Pranjal Shrivastava wrote:
> I'm not sure if I get this right.. if the user (while porting a VMM or
> something) mistakenly passes *type == IOMMU_HW_INFO_TYPE_INTEL_VTD here,
> they'll get impl-specific info?

It should call the impl hw_info which should fail?

+static void *tegra241_cmdqv_hw_info(struct arm_smmu_device *smmu, u32 *length,
+				    u32 *type)
+{
+	if (*type != IOMMU_HW_INFO_TYPE_TEGRA241_CMDQV)
+		return ERR_PTR(-EOPNOTSUPP);

If impl ops is null/etc then it fails:

+             if (!impl_ops || !impl_ops->hw_info)
+                     return ERR_PTR(-EOPNOTSUPP);

Where does IOMMU_HW_INFO_TYPE_INTEL_VTD return something?

> I agree in that case the impl-specific
> driver needs to check the type, but shouldn't we simply return from here
> itself if the type isn't arm-smmu-v3?

Then how do you return IOMMU_HW_INFO_TYPE_TEGRA241_CMDQV?

Jason