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@xxxxxxxxxx> 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. Myron > > Bjorn -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
