iommu/vt-d: Allow PCI sub-hierarchy to use DMA domain

		if ((iommu_identity_mapping & IDENTMAP_GFX) && IS_GFX_DEVICE(pdev))

			return IOMMU_DOMAIN_IDENTITY;

		/*

		 * We want to start off with all devices in the 1:1 domain, and

		 * take them out later if we find they can't access all of memory.

		 *

		 * However, we can't do this for PCI devices behind bridges,

		 * because all PCI devices behind the same bridge will end up

		 * with the same source-id on their transactions.

		 *

		 * Practically speaking, we can't change things around for these

		 * devices at run-time, because we can't be sure there'll be no

		 * DMA transactions in flight for any of their siblings.

		 *

		 * So PCI devices (unless they're on the root bus) as well as

		 * their parent PCI-PCI or PCIe-PCI bridges must be left _out_ of

		 * the 1:1 domain, just in _case_ one of their siblings turns out

		 * not to be able to map all of memory.

		 */

		if (!pci_is_pcie(pdev)) {

			if (!pci_is_root_bus(pdev->bus))

				return IOMMU_DOMAIN_DMA;

			if (pdev->class >> 8 == PCI_CLASS_BRIDGE_PCI)

				return IOMMU_DOMAIN_DMA;

		} else if (pci_pcie_type(pdev) == PCI_EXP_TYPE_PCI_BRIDGE)

			return IOMMU_DOMAIN_DMA;

	}

	return 0;