On Mon, 2013-08-19 at 14:02 -0600, Bjorn Helgaas wrote:
> On Mon, Aug 19, 2013 at 12:41 PM, Alex Williamson
> <alex.williamson@xxxxxxxxxx> wrote:
> > On Wed, 2013-08-14 at 17:06 -0600, Alex Williamson wrote:
> >> On Wed, 2013-08-14 at 16:42 -0600, Bjorn Helgaas wrote:
> >> > On Wed, Aug 14, 2013 at 2:10 PM, Alex Williamson
> >> > <alex.williamson@xxxxxxxxxx> wrote:
>
> >> > > +static int vfio_pci_for_each_slot_or_bus(struct pci_dev *pdev,
> >> > > + int (*fn)(struct pci_dev *,
> >> > > + void *data), void *data,
> >> > > + bool slot)
> >> > > +{
> >> > > + struct pci_dev *tmp;
> >> > > + int ret = 0;
> >> > > +
> >> > > + list_for_each_entry(tmp, &pdev->bus->devices, bus_list) {
> >> > > + if (slot && tmp->slot != pdev->slot)
> >> > > + continue;
> >> > > +
> >> > > + ret = fn(tmp, data);
> >> > > + if (ret)
> >> > > + break;
> >> > > +
> >> > > + if (tmp->subordinate) {
> >> > > + ret = vfio_pci_for_each_slot_or_bus(tmp, fn,
> >> > > + data, false);
> >> > > + if (ret)
> >> > > + break;
> >> > > + }
> >> > > + }
> >> > > +
> >> > > + return ret;
> >> > > +}
> >> >
> >> > vfio_pci_for_each_slot_or_bus() isn't really vfio-specific, is it?
> >>
> >> It's not, I originally has callbacks split out as PCI patches but I was
> >> able to simplify some things in the code by customizing it to my usage,
> >> so I left it here.
> >>
> >> > I mean, traversing the PCI hierarchy doesn't require vfio knowledge. I
> >> > think this loop (walking the bus->devices list) skips devices on
> >> > "virtual buses" that may be added for SR-IOV. I'm not sure that
> >> > pci_walk_bus() handles that correctly either, but at least if you used
> >> > that, we could fix the problem in one place.
> >>
> >> I didn't know about pci_walk_bus(), I'll look into switching to it.
> >
> > It looks like pci_walk_bus() is a poor replacement for when dealing with
> > slots. There might be multiple slots on a bus or a mix of slots and
> > non-slots, so for each device pci_walk_bus() finds on a subordinate bus
> > I'd need to walk up the tree to find the parent bridge on the original
> > bus to figure out if it's in the same slot.
>
> Do you really care about that scenario? PCIe only supports a single
> slot per bus, as far as I know.
I believe that's true for pciehp, but I can easily imagine that it's not
the case for other hotplug controllers. I don't run into this scenario
on any of my hardware, but I also don't want to embed any pciehp
assumptions either. So I care for the sake of completeness, but I'm not
targeting specific hardware that needs this.
> > Should we have a pci_walk_slot() function?
>
> I guess. And supply the pci_slot rather than the pci_dev? I'm a
> little bit worried because the idea of a "slot" is not well-defined in
> the spec, and we have sort of an ad hoc method of discovering and
> managing them, e.g., acpiphp and pciehp might discover the same slot.
> But I guess that's no reason to bury generic code in vfio.
I try to handle the slot as opaque, only caring that the slot pointer
matches, so I think our implementation is ok... so long as we only get
one driver claiming to manage a slot, but that's not a vfio problem ;)
Thanks,
Alex
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