2011/10/11 Bjorn Helgaas <bhelgaas@xxxxxxxxxx> > > On Fri, Oct 7, 2011 at 3:50 PM, Bjorn Helgaas <bhelgaas@xxxxxxxxxx> wrote: > > On Wed, Aug 31, 2011 at 8:48 PM, Deng-Cheng Zhu <dczhu@xxxxxxxx> wrote: > >> (Resending the patch set to include more arch maintainers.) > >> > >> Change the pci_create_bus() interface to pass in available resources to get them > >> settled down early. This is to avoid possible resource conflicts while doing > >> pci_scan_slot() in pci_scan_child_bus(). Note that pcibios_fixup_bus() can get > >> rid of such conflicts, but it's done AFTER scanning slots. > >> > >> In addition, MIPS PCI resources are now fixed using this new interface. > > > > Jesse, I assume these are headed for the 3.2 merge window, right? > > I tried to build on these patches to convert x86 to using the new > pci_create_bus() interface, but I couldn't figure out a nice way to > handle an arbitrary number of resources. > > We made pci_create_bus() take a "struct pci_bus_resource *" > (https://lkml.org/lkml/2011/8/26/88): > > struct pci_bus *pci_create_bus(struct device *parent, int bus, > struct pci_ops *ops, void *sysdata, > struct pci_bus_resource *bus_res); > > Where pci_bus_resource looks like this: > > struct pci_bus_resource { > struct list_head list; > struct resource *res; > unsigned int flags; > }; > > Conceptually, we're passing a list of resources to pci_create_bus(), > which I think is the right thing. But I think the best way to do that > is by passing a pointer to a struct list_head, not a pointer to a > pci_bus_resource. > > If we pass a pci_bus_resource, we're basically using that as a > container for a list (as per include/linux/list.h), but it's not a > well-formed list. Normally a list contains one list_head per element, > plus an extra list_head for the head of the list. There's a nice > drawing on page 296 of http://lwn.net/images/pdf/LDD3/ch11.pdf. > > The list built in your MIPS patch (https://lkml.org/lkml/2011/8/26/89) > consists of two pci_bus_resource structs (each with a list_head), but > there's no third list_head for the head of the list. I think if you > tried to use list_for_each_entry() to iterate through the list, it > would not work correctly. > > I'll post a slightly modified series to show what I mean. Take a look > and see if it makes sense to you. Yes, I can easily understand what you mean, because this point was ever considered while writing this patch series. We pass the element list as opposed to a list_head for the head of the element list because we simply want to link the elements into pci_bus->resources in pci_create_bus(). This can be done by a single line: list_add_tail(&b->resources, &bus_res->list); In addition, if we need to do list_for_each_entry() on the list, our target should always be pci_bus->resources rather than the pci_bus_resource list which is passed into pci_create_bus() to be part (the meat) of pci_bus->resources. Deng-Cheng -- 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
