Add parameter for disabling ACS redirection for P2P

Hi,

As discussed in our PCI P2PDMA series, we'd like to add a kernel parameter for selectively disabling ACS redirection for select bridges. Seeing this turned out to be a small series in itself, we've decided to send this separately from the P2P work.

This series generalizes the code already done for the resource_alignment option that already exists. The first patch creates a helper function to match PCI devices against strings based on the code that already existed in pci_specified_resource_alignment().

The second patch expands the new helper to optionally take a path of PCI devfns. This is to address Alex's renumbering concern when using simple bus-devfns. The implementation is essentially how he described it and similar to the Intel VT-d spec (Section 8.3.1).

The final patch adds the disable_acs_redir kernel parameter which takes a list of PCI devices and will disable the ACS P2P Request Redirect, ACS P2P Completion Redirect and ACS P2P Egress Control bits for the selected devices. This allows P2P traffic between selected bridges and seeing it's done at boot, before IOMMU group creating the IOMMU groups will be created correctly based on the bits.

Thanks,

Logan

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Changes since v1:

* Reworked pci_dev_str_match_path using strrchr as suggested by Alex
* Collected Christian's Acks

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Logan Gunthorpe (3):
PCI: Make specifying PCI devices in kernel parameters reusable
PCI: Allow specifying devices using a base bus and path of devfns
PCI: Introduce the disable_acs_redir parameter

 Documentation/admin-guide/kernel-parameters.txt |  39 ++-
 drivers/pci/pci.c                               | 353 ++++++++++++++++++++----
 2 files changed, 331 insertions(+), 61 deletions(-)

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2.11.0