linux-kernel - Re: [PATCH v3 08/15] iommu/amd: Use pci_find_dma_isolation

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Date:	Wed, 14 May 2014 12:34:50 +0200
From:	Joerg Roedel <joro@...tes.org>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	linux-pci@...r.kernel.org, iommu@...ts.linux-foundation.org,
	bhelgaas@...gle.com, acooks@...il.com,
	linux-kernel@...r.kernel.org, linux@...izon.com
Subject: Re: [PATCH v3 08/15] iommu/amd: Use pci_find_dma_isolation_root()
 for IOMMU groups

On Sat, May 10, 2014 at 09:03:11AM -0600, Alex Williamson wrote:
> The expectation is that the kernel and IVRS will produce the same
> result for topology based aliases while the kernel will also include
> device specific DMA quirks.

Is that expectation really true? There are PCIe devices out there that
don't use their own device-id for requests but another one that isn't
even visible as a PCI device (so the kernel has no pci_dev structure for
it). The IVRS table contains such information, but I am not sure whether
the PCI core finds the right requestor-id for those devices.

I've seen this on PCIe cards that where the vendor just used an PCI-X
chip with a PCIe-to-PCI-X bridge on the card. The PCI-X device is
visible for the OS but uses the requestor-id of the invisible bridge.

	Joerg

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