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    SubjectRe: [PATCH 2/2] PCI, ACPI, x86: update MMCFG information when hot-plugging PCI host bridges
    (2012/04/10 1:02), Jiang Liu wrote:
    > Hi Kenji,
    > Thanks for your careful review and comments.
    >
    > On 04/09/2012 07:43 PM, Kenji Kaneshige wrote:
    >> Your patch looks good to me.
    >>
    >> I have some comments.
    >>
    >> (2012/04/09 2:12), Jiang Liu wrote:
    >>> This patch enhances pci_root driver to update MMCFG information when
    >>> hot-plugging PCI root bridges on x86 platforms.
    >>>
    >>
    >> Do you have the patch that can be applied to Bjorn's pci tree?
    >>
    >> <snip.>
    > Will try to generate a version against Bjorn's version. Could you please tell
    > me the exact git link for that? I haven't pull from Bjorn's tree yet.

    As you may know, it was announced _today_ (sorry:).

    http://www.spinics.net/lists/linux-pci/msg14626.html

    >
    >>
    >>> +int arch_acpi_pci_root_add(struct acpi_pci_root *root)
    >>> +{
    >>> + int result = 0;
    >>> + acpi_status status;
    >>> + unsigned long long base_addr;
    >>> + struct pci_mmcfg_region *cfg;
    >>> +
    >>> + /*
    >>> + * Try to insert MMCFG information for host bridges with _CBA method
    >>> + */
    >>> + status = acpi_evaluate_integer(root->device->handle, METHOD_NAME__CBA,
    >>> + NULL,&base_addr);
    >>> + if (ACPI_SUCCESS(status)) {
    >>> + result = pci_mmconfig_insert(root->segment,
    >>> + root->secondary.start,
    >>> + root->secondary.end,
    >>> + base_addr);
    >>> + /*
    >>> + * MMCFG information for hot-pluggable host bridges may have
    >>> + * already been added by __pci_mmcfg_init();
    >>> + */
    >>> + if (result == -EEXIST)
    >>> + result = 0;
    >>
    >> Just for confirmation.
    >> From my interpretation of PCI firmware spec, MCFG doesn't have any entry
    >> for hot-pluggable hostbridge. So I assume this is for the machine that
    >> is not compliant to the spec. Is my understanding same as yours?
    >>
    >> <snip.>
    > You are right, it's defined to that way in PCI FW Spec 3.1.
    > Here I have some concerns about the PCI buses to host all Ubox components
    > on Intel NHM/WSM/SNB/IVB processors. BIOS people are prone to declare
    > MMCFG information for those host bridges by MCFG table instead of _CBA method,
    > though those host bridge will disappear after hot-removing a physical processor.

    Ok, thank you for clarification.

    >
    >>
    >>> static int __devinit acpi_pci_root_add(struct acpi_device *device)
    >>> {
    >>> unsigned long long segment, bus;
    >>> @@ -504,6 +514,14 @@ static int __devinit acpi_pci_root_add(struct acpi_device *device)
    >>> strcpy(acpi_device_class(device), ACPI_PCI_ROOT_CLASS);
    >>> device->driver_data = root;
    >>>
    >>> + if (arch_acpi_pci_root_add(root)) {
    >>> + printk(KERN_ERR PREFIX
    >>> + "can't add MMCFG information for Bus %04x:%02x\n",
    >>> + root->segment, (unsigned int)root->secondary.start);

    Additional comment.

    This printk message looks strange because arch_acpi_pci_root_add()
    is not a mmconfig specific function. So I think this message
    should be moved to arch specific code (arch_acpi_pci_root_add()).

    >>> + result = -ENODEV;
    >>> + goto out_free;
    >>> + }
    >>
    >> Desn't this break the system that doesn't support MMCONFIG?
    >>
    >> In my understanding, arch_acpi_pci_root_add() returns -ENODEV if
    >> mmconfig information is found neither in MCFG table nor _CBA. And
    >> pci root bridge initialization seems to fail arch_acpi_pci_root_add()
    >> returns non-zero value.
    > Good catch, will add following code into arch_acpi_pci_root_add() and
    > arch_acpi_pci_root_remove() to solve this issue.
    > ---
    > /* MMCONFIG disabled */
    > if ((pci_probe& PCI_PROBE_MMCONF) == 0)
    > return 0;
    > ---

    My understanding is that PCI_PROBE_MMCONF is set even if the system
    doesn't have MCFG table. So I don't think this solves the issue. I
    guess this is what Yinghai pointed out on your V2 patch [6/6].

    Additionally, I think there is a remaining issue even if we change
    this check like below.

    if (!!(pci_probe & PCI_PROBE_MASK & ~PCI_PROBE_MMCONF))
    return 0;

    I think this check has an assumption that system has at least one
    MCFG table entry and it has been initialized before
    acpi_pci_root_add() is called. I think this doesn't work on the
    system that doesn't have MCFG and all the pci root bridge have
    _CBA (that is, all host bridges are hot-pluggable and BIOS is
    implemented in the way PCI FW spec defines). As a result, MMCONFIG
    would never be enabled on such systems. Could you double check this?

    Regards,
    Kenji Kaneshige


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