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    SubjectRe: [RESEND PATCH v3 0/2] Pass resources to pci_create_bus() and fix MIPS PCI resources
    On Fri, Oct 7, 2011 at 3:50 PM, Bjorn Helgaas <bhelgaas@google.com> wrote:
    > On Wed, Aug 31, 2011 at 8:48 PM, Deng-Cheng Zhu <dczhu@mips.com> wrote:
    >> (Resending the patch set to include more arch maintainers.)
    >>
    >> Change the pci_create_bus() interface to pass in available resources to get them
    >> settled down early. This is to avoid possible resource conflicts while doing
    >> pci_scan_slot() in pci_scan_child_bus(). Note that pcibios_fixup_bus() can get
    >> rid of such conflicts, but it's done AFTER scanning slots.
    >>
    >> In addition, MIPS PCI resources are now fixed using this new interface.
    >
    > Jesse, I assume these are headed for the 3.2 merge window, right?

    I tried to build on these patches to convert x86 to using the new
    pci_create_bus() interface, but I couldn't figure out a nice way to
    handle an arbitrary number of resources.

    We made pci_create_bus() take a "struct pci_bus_resource *"
    (https://lkml.org/lkml/2011/8/26/88):

    struct pci_bus *pci_create_bus(struct device *parent, int bus,
    struct pci_ops *ops, void *sysdata,
    struct pci_bus_resource *bus_res);

    Where pci_bus_resource looks like this:

    struct pci_bus_resource {
    struct list_head list;
    struct resource *res;
    unsigned int flags;
    };

    Conceptually, we're passing a list of resources to pci_create_bus(),
    which I think is the right thing. But I think the best way to do that
    is by passing a pointer to a struct list_head, not a pointer to a
    pci_bus_resource.

    If we pass a pci_bus_resource, we're basically using that as a
    container for a list (as per include/linux/list.h), but it's not a
    well-formed list. Normally a list contains one list_head per element,
    plus an extra list_head for the head of the list. There's a nice
    drawing on page 296 of http://lwn.net/images/pdf/LDD3/ch11.pdf.

    The list built in your MIPS patch (https://lkml.org/lkml/2011/8/26/89)
    consists of two pci_bus_resource structs (each with a list_head), but
    there's no third list_head for the head of the list. I think if you
    tried to use list_for_each_entry() to iterate through the list, it
    would not work correctly.

    I'll post a slightly modified series to show what I mean. Take a look
    and see if it makes sense to you.

    Bjorn


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