linux-kernel - Re: [RFC 2/8] iommu: Add a helper to check if any iommu device is registered

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Message-ID: <20251203131129.GD1109247@nvidia.com>
Date: Wed, 3 Dec 2025 09:11:29 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: Jacob Pan <jacob.pan@...ux.microsoft.com>
Cc: Baolu Lu <baolu.lu@...ux.intel.com>, linux-kernel@...r.kernel.org,
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	Alex Williamson <alex.williamson@...hat.com>,
	Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
	Robin Murphy <robin.murphy@....com>,
	Nicolin Chen <nicolinc@...dia.com>,
	"Tian, Kevin" <kevin.tian@...el.com>,
	"Liu, Yi L" <yi.l.liu@...el.com>, skhawaja@...gle.com,
	pasha.tatashin@...een.com, Zhang Yu <zhangyu1@...ux.microsoft.com>,
	Jean Philippe-Brucker <jean-philippe@...aro.org>,
	David Matlack <dmatlack@...gle.com>,
	Alex Williamson <alex@...zbot.org>
Subject: Re: [RFC 2/8] iommu: Add a helper to check if any iommu device is
 registered

On Tue, Dec 02, 2025 at 04:06:35PM -0800, Jacob Pan wrote:
> However, as you pointed out there seems to be no standard ordering
> for iommu device registration across platforms. e.g. VT-d hooks up with
> x86_init, smmuv3 does that in platform driver probe. This patchset puts
> dummy driver under early_initcall which is after both but not a
> guarantee for all platforms. Any suggestions?

I think we need to do something more like the sefltest does and
manually bind a driver to a device so this init time ordering
shouldn't matter.

IDK maybe a fake iommu driver has too many problems :\

Jason