On Fri, Sep 12, 2014 at 09:18:18PM -0600, Bjorn Helgaas wrote:
> On Thu, Sep 11, 2014 at 10:13:09AM +0200, David Henningsson wrote:
> >
> >
> > On 2014-09-10 20:08, Bjorn Helgaas wrote:
> > >[+cc Andreas]
> > >v3.16 fails with:
> > >
> > > pci 0000:01:01.0: can't allocate child bus 01 from [bus 01]
> > >
> > >which Andreas added with fc1b253141b3 ("PCI: Don't scan random busses
> > >in pci_scan_bridge()"). But I don't understand that code well enough
> > >to know whether this commit is actually the cause of the problem.
> > >
> > >And I also haven't figured out how "pci=assign-busses" makes a difference.
> > >
> > >David, would you mind turning on CONFIG_DYNAMIC_DEBUG=y in your v3.16
> > >kernel, adding 'dyndbg="file probe.c +p"' to your boot arguments, and
> > >collecting another dmesg log?
> >
> > Thanks for looking at this (and sorry for not having done a bisect yet).
> >
> > Anyhow, a new dmesg log has now been posted at kernel bugzilla
> > #83441. It has a few more lines starting with "pci_bus" but nothing
> > that really stands out AFAICT.
>
> We need to make progress on this regression before v3.17. David, can you
> test the following revert (on top of v3.17-rc2)? If it works, I plan to
> apply it for v3.17 (unless we have a better solution, of course).
David reported at https://bugzilla.kernel.org/show_bug.cgi?id=83441#c7 that
the revert below did fix the problem, so I'm going to apply it for v3.17.
I'd prefer to use something like Andreas' pci_grow_bus() patch, but I don't
think it's going to be ready in time for v3.17. I hope we can polish that
for v3.18 or v3.19.
Bjorn
> commit 413db4234ebbb9750f01180c04965ad3a5e18986
> Author: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> Date: Fri Sep 12 20:46:09 2014 -0600
>
> Revert "PCI: Don't scan random busses in pci_scan_bridge()"
>
> This reverts commit fc1b253141b3 ("PCI: Don't scan random busses in
> pci_scan_bridge()") because it breaks CardBus on some machines.
>
> David tested a Dell Latitude D505 that worked like this prior to
> fc1b253141b3:
>
> pci 0000:00:1e.0: PCI bridge to [bus 01]
> pci 0000:01:01.0: CardBus bridge to [bus 02-05]
>
> Note that the 01:01.0 CardBus bridge has a bus number aperture of
> [bus 02-05], but those buses are all outside the 00:1e.0 PCI bridge bus
> number aperture, so accesses to buses 02-05 never reach CardBus. This is
> later patched up by yenta_fixup_parent_bridge(), which changes the
> subordinate bus number of the 00:1e.0 PCI bridge:
>
> pci_bus 0000:01: Raising subordinate bus# of parent bus (#01) from #01 to #05
>
> With fc1b253141b3, pci_scan_bridge() just fails immediately when it notices
> that we can't allocate a valid secondary bus number for the CardBus bridge,
> and CardBus doesn't work at all:
>
> pci 0000:01:01.0: can't allocate child bus 01 from [bus 01]
>
> I'd prefer to fix this by integrating the yenta_fixup_parent_bridge() logic
> into pci_scan_bridge() so we fix the bus number apertures up front. But
> that's a bigger effort, and I want to fix the regression while we're
> working on it.
>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=83441
> Link: http://lkml.kernel.org/r/1409303414-5196-1-git-send-email-david.henningsson@xxxxxxxxxxxxx
> Reported-by: David Henningsson <david.henningsson@xxxxxxxxxxxxx>
> Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> CC: stable@xxxxxxxxxxxxxxx # v3.15+
>
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index e3cf8a2e6292..7c8ca351beae 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -838,16 +838,12 @@ int pci_scan_bridge(struct pci_bus *bus, struct pci_dev *dev, int max, int pass)
> goto out;
> }
>
> - if (max >= bus->busn_res.end) {
> - dev_warn(&dev->dev, "can't allocate child bus %02x from %pR\n",
> - max, &bus->busn_res);
> - goto out;
> - }
> -
> /* Clear errors */
> pci_write_config_word(dev, PCI_STATUS, 0xffff);
>
> - /* The bus will already exist if we are rescanning */
> + /* Prevent assigning a bus number that already exists.
> + * This can happen when a bridge is hot-plugged, so in
> + * this case we only re-scan this bus. */
> child = pci_find_bus(pci_domain_nr(bus), max+1);
> if (!child) {
> child = pci_add_new_bus(bus, dev, max+1);
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