From: Myron Stowe <myron.stowe@redhat.com>
Subject: [PATCH 0/4] PCI: PCIe capability structure related cleanup/fixes
To: bhelgaas@google.com
Cc: linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
        xudong.hao@linux.intel.com, ddutile@redhat.com, yu.zhao@intel.com
Date: Fri, 01 Jun 2012 15:16:19 -0600
Message-ID: <20120601211619.20328.36769.stgit@amt.stowe>
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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.


 drivers/pci/pci.c        |   93 ++++++++++++++++++++++++++++------------------
 include/linux/pci.h      |    1 
 include/linux/pci_regs.h |    7 +++
 3 files changed, 64 insertions(+), 37 deletions(-)

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