pci-hyperv.c and pci_bus_assign_resources()

pci-hyperv.c and pci_bus_assign_resources()

[Benjamin Herrenschmidt]

Hi Folks !

As part of my consolidation of the PCI resource survey, pci-hyperv is
getting a bit in the way, I need help understanding what exactly it
needs here when it calls pci_bus_assign_resources().

As you can see at:

https://git.kernel.org/pub/scm/linux/kernel/git/benh/pci.git/

I have removed all call sites of pci_bus_assign_resources() except that
one.

So far, as far as I understand and provided I didn't screw up, they
were all either part of a pair doing:

	pci_bus_size_bridges(bus);
	pci_bus_assign_resources(bus);

or trying to assign a single added device, or buggy controller code who
did pci_bus_assign_resources() without doing pci_bus_size_bridges()
first.

pci-hyperv is a bit of a mystery however. The call to
pci_bus_assign_resources() alone will try to assign resources to
devices but will not assign anything to bridges. So any bridge will be
left as-is. Now on x86, pcibios_fixup_bus() will call
pci_read_bridge_bases(), so any such bridge will at least get its
resources read from the hw, but not allocated (parent won't be set).

So it all a bit odd ...

What is the context here ? What may be hanging off that bus when it's
added ? Should it be calling pci_assign_unassigned_bridge_resources()
instead like other hotplug drivers do ? Something else ?

Thanks !

Cheers,
Ben.