On Mon, Apr 30, 2012 at 9:02 PM, Bjorn Helgaas <bhelgaas@xxxxxxxxxx> wrote:
> 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.
there are about 70 bus->subordinate reference and 40 bus->secondary reference.
could try to update them in following patch set.
>
> 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.
busn alloc will try to solve x-y may need big range than [a,b], it
will extend top of b and parents of bus a.
instead of just b+1 blindly.
and will have more strict checking to avoid overlapping.
>
>> 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.
Using busn_res to track and allocate busn range, by put them in the
resource tree could reuse resource allocating code.
Yinghai
--
To unsubscribe from this list: send the line "unsubscribe linux-pci" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
