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To:     Robin Murphy <robin.murphy@arm.com>,
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Subject: RE: [PATCH v3 03/15] iommu: Always register bus notifiers
Thread-Topic: [PATCH v3 03/15] iommu: Always register bus notifiers
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Date:   Thu, 7 Jul 2022 06:31:31 +0000
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> From: Robin Murphy <robin.murphy@arm.com>
> Sent: Wednesday, July 6, 2022 1:08 AM
>=20
> The number of bus types that the IOMMU subsystem deals with is small and
> manageable, so pull that list into core code as a first step towards
> cleaning up all the boilerplate bus-awareness from drivers. Calling
> iommu_probe_device() before bus->iommu_ops is set will simply return
> -ENODEV and not break the notifier call chain, so there should be no
> harm in proactively registering all our bus notifiers at init time.
>=20

Suppose we miss a check on iommu ops in iommu_release_device():

	if (!dev->iommu) <<<<<<<
		return;

	iommu_device_unlink(dev->iommu->iommu_dev, dev);

	ops =3D dev_iommu_ops(dev);
	ops->release_device(dev);

following the rationale in patch01 a device could be removed when
it's associated with a known but not registered instance.