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    SubjectRe: [PATCH 08/18] PCI, powerpc: Register busn_res for root buses
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    On Mon, 2012-02-27 at 22:36 -0700, Bjorn Helgaas wrote:
    >
    > There's a lot of powerpc code that does this:
    >
    > bus_range = of_get_property(pcictrl, "bus-range", &len);
    > hose->first_busno = bus_range[0];
    > hose->last_busno = bus_range[1];
    >
    > That *looks* like it is discovering the bus number aperture. Is it?
    > If it is, why are we using the largest bus number found by
    > pci_scan_child_bus() rather than "last_busno"?

    We do that but we somewhat -also- rely on the core bumping it if it
    needs to make room :-)

    As I said, we are swimming in dirty waters between reverse engineered
    stuff we don't know 100% and "designed" stuff.

    I think we should have ways to more explicitely define what we want tho,
    ie whether hose->last_busno is just what happens to be the "current" bus
    number assigned by the firmware or the hard max. Maybe a pci flag ?

    On the other hand some platforms (all the ppc4xx ones for example) set
    the flag to reassign all busses ... but have limit on bus numbers simply
    because they have a memory mapped only config space and we don't have
    enough address space to ioremap it all on 32-bit.

    We need to fix them to use a fixmap entry to do atomic on-demand mapping
    of the config space and lift that restriction, but that isn't done yet.

    So I think those patches will need really careful handling on our side.

    Cheers,
    Ben.




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