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    SubjectRe: [PATCH 0/1] Recurse when searching for empty slots in resources trees
    On Tue, 16 Jun 2009 16:56:12 -0700 (PDT)
    Linus Torvalds <torvalds@linux-foundation.org> wrote:

    >
    >
    > On Tue, 16 Jun 2009, Andrew Patterson wrote:
    > > >
    > > > Well, find_resource() found room for a resource. So it returns
    > > > it. The point is, your patch returns another - equally valid one.
    > >
    > > I am confused. The existing code will return a conflict and bomb
    > > out.
    >
    > My point is, there are two answers - returning the conflicting
    > resource, or trying to recurse into it. Both are "valid", in the
    > sense that both have real semantics.
    >
    > But the reason I don't like your patch is that I think the _deeper_
    > problem is the fact that the resource tree isn't set up right in the
    > first place.
    >
    > It looks to me like your patch works around the bug (by trying to
    > find that "other possible case"), while my disagreement with that
    > patch is that we should never need to care about these kinds of "you
    > can try to find ambiguous cases" in the first place.
    >
    > > > We've had those kinds of situations before. The thread you point
    > > > to is an exact case of this. My point is that I'd rather try to
    > > > _avoid_ any ambiguous cases, and try to solve it properly at a
    > > > higher PCI level, where the ambiguity doesn't exist any more
    > > > (because we'd explicitly take the actual bus topology into
    > > > account). So your patch may fix a bug, but I'm pretty sure I've
    > > > seen a patch from Ivan that should _also_ fix it, and that I
    > > > would expect to do it not by just tweaking a fundamentally
    > > > ambiguous case.
    > >
    > > OK. I would be happy to test Ivan's patch.
    >
    > I just looked at our PCI bus resource allocation code, and afaik it
    > does everything right even as-is. Which is why I now wonder if that
    > incorrectly nested bus resource was perhaps set up by the PCI hotplug
    > code (which I do not know, and didn't look at).
    >
    > I may also be confused, and not have found the right place that
    > actually inserts the resource. Afaik, bus resources get allocated
    > through
    >
    > pbus_assign_resources_sorted ->
    > pci_assign_resource ->
    > pci_bus_alloc_resource ->
    > allocate_resource
    >
    > and that "pci_bus_alloc_resource()" thing only allocates within the
    > parent bus, so it _should_ nest correctly.
    >
    > It would be interesting to see where that resource actually gets
    > allocated. I'm clearly missing something, since clearly your
    > resources do _not_ nest correctly.

    Alex has been fixing up hotplug related code recently too; Alex? Also
    you didn't actually include a patch in your last mail that I could
    see...

    --
    Jesse Barnes, Intel Open Source Technology Center


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