linux-kernel - Re: [PATCH v2 3/7] iommu: Make iommu_dma_prepare

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Message-ID: <20250221164400.GN50639@nvidia.com>
Date: Fri, 21 Feb 2025 12:44:00 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: Robin Murphy <robin.murphy@....com>
Cc: Nicolin Chen <nicolinc@...dia.com>, kevin.tian@...el.com,
	tglx@...utronix.de, maz@...nel.org, joro@...tes.org,
	will@...nel.org, shuah@...nel.org, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kselftest@...r.kernel.org, eric.auger@...hat.com,
	baolu.lu@...ux.intel.com, yi.l.liu@...el.com, yury.norov@...il.com,
	jacob.pan@...ux.microsoft.com, patches@...ts.linux.dev
Subject: Re: [PATCH v2 3/7] iommu: Make iommu_dma_prepare_msi() into a
 generic operation

On Fri, Feb 21, 2025 at 03:39:45PM +0000, Robin Murphy wrote:
> Yuck. Realistically we are going to have no more than two different
> implementations of this; a fiddly callback interface seems overkill. All we
> should need in the domain is a simple indicator of *which* MSI translation
> scheme is in use (if it can't be squeezed into the domain type itself), then
> iommu_dma_prepare_msi() can simply dispatch between iommu-dma and IOMMUFD
> based on that, and then it's easy to solve all the other fragility issues
> too.

That would make module dependency problems, we have so far avoided
having the core kernel hard depend on iommufd.

Jason