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    SubjectRe: [PATCH 0/4] PCI: PCIe capability structure related cleanup/fixes
    On Tue, Jun 12, 2012 at 10:34 AM, Myron Stowe <mstowe@redhat.com> wrote:
    > On Mon, 2012-06-11 at 19:52 -0700, Bjorn Helgaas wrote:
    >> On Fri, Jun 1, 2012 at 2:16 PM, Myron Stowe <myron.stowe@redhat.com> wrote:
    >> > The following series introduces PCI Express 'capability structure'
    >> > related cleanup, fixes, and optimizations.
    >> >
    >> > Patch 1/4 changes pci_ltr_supported() to a static routine.
    >> >
    >> > Patch 2/4 removes redundant checking in various PCI Express features as
    >> > suggested by Bjorn Helgaas in
    >> > http://marc.info/?l=linux-pci&m=130463494319762&w=2
    >> >
    >> > There is a similar idiom in use that could be similarly be re-factored:
    >> >    if (!pci_is_pcie(dev))
    >> >        return;
    >> >
    >> >    pos = pci_find_ext_capability(dev, ...);
    >> >    if (!pos)
    >> >        return;
    >> >
    >> > At first it seemed incorrect to remove the redundant call of
    >> > pci_is_pcie() in these cases as a PCI or PCI-X (< 2.0) device may be
    >> > involved.  In such cases an "extended capability" list would not exist,
    >> > as it was not introduced until PCI-X 2.0, and accesses outside of the
    >> > device's configuration space would be attempted.  However, upon further
    >> > review of pci_find_ext_capability() it looks as if such accesses would
    >> > be handled correctly due to the short-circuiting logic involved -
    >> >
    >> >    if (pci_read_config_dword(dev, pos, &header) != PCIBIOS_SUCCESSFUL)
    >> >        return 0;
    >> >
    >> > As such, I'll entertain comments as to whether or not we should also
    >> > make similar removals of pci_is_pcie() in these cases.
    >> >
    >> > Patch 3/4 introduces pci_pcie_cap2() for use in v2 capability related
    >> > feature code.  The makeup of Express' capability structure varies
    >> > substantially between v1 and v2.
    >> >
    >> > There is still some redundancy in PCIe v2 capabilities checking related
    >> > to the Latency Tolerance Reporting (LTR) feature routines that likely
    >> > could be re-factored further; please feel free to respond with ideas.
    >> >
    >> > Patch 4/4 makes a minor optimization to the saving and restoring of
    >> > PCI Express capability structures.
    >> >
    >> > Seems like the same type of optimization could be done to remove the
    >> > 'if (pcie_cap_has_lnkctl(dev->pcie_type, flags))' check.  According to
    >> > section 7.8 "PCI Express Capability Structure" of the PCI Express 1.0a
    >> > specification:
    >> >
    >> >    "Figure 7-10 details allocation of register fields in the PCI
    >> >     Express Capability structure. The PCI Express Capabilities,
    >> >     Device Capabilities, Device Status/Control, Link Capabilities,
    >> >     and Link Status/Control registers are required for all PCI
    >> >     Express devices. Endpoints are not required to implement
    >> >     registers other than those listed above and terminate the
    >> >     capability structure."
    >> >
    >> > There may have been some early Express devices that did not properly
    >> > follow the specification which required the introduction of
    >> > 'pcie_cap_has_lnkctl()' so I did not make the additional optimization.
    >> > ---
    >> >
    >> > Myron Stowe (4):
    >> >      PCI: Remove redundant capabilities checking in pci_{save,restore}_pcie_state
    >> >      PCI: Add pci_pcie_cap2() check for PCIe feature capabilities >= v2
    >> >      PCI: Remove redundant checking in PCI Express capability routines
    >> >      PCI: make pci_ltr_supported static.
    >>
    >> I added Don's acks, made a couple minor changes he suggested, removed
    >> the static pci_ltr_supported() function declaration (unnecessary,
    >> AFAICS), and pushed these to:
    >>
    >>   http://git.kernel.org/?p=linux/kernel/git/helgaas/pci.git;a=shortlog;h=refs/heads/topic/stowe-cap-cleanup
    >>
    >> If everything looks right to you, I'll merge it into "next" tomorrow.
    >> Thanks for doing this; I think it's some nice cleanup and will make
    >> things safer and easier to understand.
    >
    > Looks good - thanks to both Don and yourself for the suggestions and
    > changes to make the patch headers more comprehensible with respect to
    > the capabilities structure versions.

    Great, I merged that topic branch to "next" and pushed it.

    Bjorn
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