MIME-Version: 1.0
In-Reply-To: <20120601211619.20328.36769.stgit@amt.stowe>
References: <20120601211619.20328.36769.stgit@amt.stowe>
From: Bjorn Helgaas <bhelgaas@google.com>
Date: Mon, 11 Jun 2012 19:52:03 -0700
Message-ID: <CAErSpo5yZdr4dgqjO6O9PSi3XZXfSOHmjjJRemaqAfmpv5WREA@mail.gmail.com>
Subject: Re: [PATCH 0/4] PCI: PCIe capability structure related cleanup/fixes
To: Myron Stowe <myron.stowe@redhat.com>
Cc: linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
        xudong.hao@linux.intel.com, ddutile@redhat.com, yu.zhao@intel.com
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 8BIT
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 3719
Lines: 83

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.

Bjorn
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/