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SubjectRe: [patch non-x86] PCI-PCI bridges fix
Ivan Kokshaysky writes:

> Bridge resources weren't added to the resource tree. This was
> harmless for most real-life configurations (especially on Alpha),
> but certainly it will be a problem with the hotplug stuff
> (thinking of ES45).
> Ivan.
> --- 2.4.15p9/drivers/pci/setup-bus.c Fri Oct 5 05:47:08 2001
> +++ linux/drivers/pci/setup-bus.c Wed Nov 21 20:16:24 2001
> @@ -201,6 +201,16 @@ pbus_assign_resources(struct pci_bus *bu
> b->resource[0]->end = ranges->io_end - 1;
> b->resource[1]->end = ranges->mem_end - 1;
> + /* Add bridge resources to the resource tree. */
> + if (b->resource[0]->end > b->resource[0]->start &&
> + request_resource(bus->resource[0], b->resource[0]) < 0)
> + printk(KERN_ERR "PCI: failed to reserve IO "
> + "for bus %d\n", b->number);

There is code in pci_read_bridge_bases which will decide under some
circumstances that a PCI-PCI bridge is transparent and set

child->resource[i] = child->parent->resource[i];

for i = 0, 1 or 2. What will happen with your request_resource in
this case is that the resource will end up being its own parent and
its own child and all allocations against it will fail. :)

I hit this just yesterday on PPC. On our RS/6000 boxes, if you have a
PCI-PCI bridge with nothing behind it, the firmware will configure it
with all the apertures closed, i.e. with base set larger than limit.
Then pci_read_bridge_bases goes and decides that the bridge is
transparent and consequently everything stops working. :(

Does anyone really need that "assuming transparent" stuff in
pci_read_bridge_bases? If so we need to add a check for the case
where base == limit + 0x1000 (for I/O) or base == limit + 0x100000
(for memory) and conclude that the aperture is closed in that case.

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