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Alex Williamson authored
When a PCI-to-PCIe bridge is stacked on a PCIe-to-PCI bridge, we can have PCIe endpoints masked by a conventional PCI bus. This makes the extended config space of the PCIe endpoint inaccessible. The PCIe-to-PCI bridge is supposed to handle any type 1 configuration transactions where the extended config offset bits are non-zero as an Unsupported Request rather than forward it to the secondary interface. As noted here, there are a couple known offenders to this rule. These bridges drop the extended offset bits, resulting in the conventional config space being aliased many times across the extended config space. For Intel NICs, this alias often seems to expose a bogus SR-IOV cap. Stacking bridges may seem like an uncommon scenario, but note that any conventional PCI slot in a modern PC is already the secondary interface of an onboard PCIe-to-PCI bridge. The user need only add a PCI-to-PCIe adapter and PCIe device to encounter this problem. Signed-off-by: Alex Williamson <alex.williamson@redhat.com> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
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