On Mon, Apr 30, 2012 at 6:32 PM, Yinghai Lu <yinghai@xxxxxxxxxx> wrote:
> On Mon, Apr 30, 2012 at 4:25 PM, Bjorn Helgaas <bhelgaas@xxxxxxxxxx> wrote:
>>> --- a/include/linux/pci.h
>>> +++ b/include/linux/pci.h
>>> @@ -419,6 +419,7 @@ struct pci_bus {
>>> struct list_head slots; /* list of slots on this bus */
>>> struct resource *resource[PCI_BRIDGE_RESOURCE_NUM];
>>> struct list_head resources; /* address space routed to this bus */
>>> + struct resource busn_res; /* track registered bus num range */
>>>
>>> struct pci_ops *ops; /* configuration access functions */
>>> void *sysdata; /* hook for sys-specific extension */
>>
>> struct pci_bus already includes "secondary" and "subordinate". This
>> new "busn_res" looks like it will contain the same information. Why
>> do we need both?
>
> In some case the could be different.
> for root bus from _CRS, busn_res could bigger than subordinate,
> because scan_childbus will update subordinate.
For a bus below a P2P bridge, I think it's always the case that the
bridge's Subordinate Bus Number in config space == bus->subordinate ==
bus->busn_res.end (correct me if I'm wrong). I don't like the
redundancy in this case.
For a root bus where you set bus->busn_res from _CRS and
bus->subordinate = pci_scan_child_bus(), bus->busn_res.end will
generally be different from bus->subordinate, but there's no point in
keeping track of bus->subordinate.
The reason we care about secondary and subordinate is so we can
allocate bus numbers when enumerating devices behind a bridge. The
only thing we need for that is the aperture of the upstream bridge and
the apertures of any peer bridges on the same bus. Let's say we have
this:
pci 00:00.0 bridge to [bus a-b]
pci a:01.0 bridge to [bus c-d] (already enumerated)
pci a:02.0 bridge to [bus e-f] (already enumerated)
pci a:03.0 bridge to [bus x-y] (enumerating now)
We know [c-d] is contained in [a-b]; [e-f] is contained in [a-b]; a <
c; and a < e. To enumerate behind a:03.0, we need to assign x & y
such that a < x; [x-y] is contained in [a-b]; and [x-y] does not
overlap [c-d] or [e-f]. The value from pci_scan_child_bus() is
probably useful for setting y, but we don't have to save it in the
struct pci_bus for that.
> and also we have one resource to insert it into the resource tree, so
> later could probe/allocate bus num range.
Sorry, I didn't understand this.
Bjorn
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