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. 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
