linux-kernel - Re: [PATCH v4 18/23] iommu/arm-smmu-v3-iommufd: Support implementation-defined hw

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Message-ID: <aCY31VOs62/OAaca@Asurada-Nvidia>
Date: Thu, 15 May 2025 11:52:05 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: <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>,
	<praan@...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>
Subject: Re: [PATCH v4 18/23] iommu/arm-smmu-v3-iommufd: Support
 implementation-defined hw_info

On Thu, May 15, 2025 at 02:17:06PM -0300, Jason Gunthorpe wrote:
> On Thu, May 08, 2025 at 08:02:39PM -0700, Nicolin Chen wrote:
> > Repurpose the @__reserved field in the struct iommu_hw_info_arm_smmuv3,
> > to an HW implementation-defined field @impl.
> 
> It would be nicer to have a tegra/cmdq specific struct and a way for
> iommu_hw_info to select it. 'impl' isn't going to scale very well if
> something else wants to use this.
> 
> We have out_data_type but we could have an input sub_data_type too. 0
> means what we have today, then a simple enum to select another info
> struct.

So, there will be two hw_info calls back to back right?

Should the first call return out_data_type=CMDQV while returning
the arm_smmu_v3 hw_info data? Otherwise, VMM wouldn't know what
to set in the input sub_data_type of the 2nd ioctl?

Thanks
Nicolin