From: Robin Murphy <robin.murphy@arm.com>
Sent: Wednesday, July 6, 2022 1:08 AM

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.

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 = 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.

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