On Thu, Mar 12, 2015 at 09:03:12PM +0800, Yijing Wang wrote: > On 2015/3/12 10:55, Bjorn Helgaas wrote: > > On Mon, Mar 09, 2015 at 10:34:07AM +0800, Yijing Wang wrote: > >> Introduce pci_host_bridge_list to manage pci host > >> bridges in system, so we could detect whether > >> the host in domain:bus is alreay registered. > >> Then we could remove bus alreay exist test in > >> __pci_create_root_bus(). > > > > It's a nice idea to move this test into the core. While you're at it, why > > don't you check for any overlap with the bus ranges of existing host > > bridges? For example, if we're trying to create a new host bridge to > > [bus 40-7f], it should conflict with existing bridges to [bus 00-7f] > > as well as to [bus 40-ff]. I think your current patch will detect the > > latter conflict but not the former. > > Now pci host bridge may only know its start bus number, like acpi _BBN provided, > but does not limit the end bus number, Eg. two pci roots report _BBN 0x0 and 0x80, > so we have two bus number resource (0, 0xff) and (0x80, 0xff), if we check it strictly, > some pci scan would fail which currently scan success. _BBN is not the correct source for the bridge's bus number range. There's a comment in acpi_pci_root_add() that explains why: * We need both the start and end of the downstream bus range * to interpret _CBA (MMCONFIG base address), so it really is * supposed to be in _CRS. If we don't find it there, all we * can do is assume [_BBN-0xFF] or [0-0xFF]. A platform SHOULD know the start and and end bus number. If it doesn't I think it's the platform's responsibility to carve up the bus number range. Maybe this can be done by trimming the range of the [bus 00-ff] bridge when we discover another bridge that leads to bus 80. -- 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
