Re: [PATCH] PCI: workaround hard-wired bus number

[Jesse Barnes <jbarnes@virtuousgeek.org>]

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On Fri, 27 Jan 2012 09:26:16 -0700
Bjorn Helgaas <bhelgaas@google.com> wrote:

> On Fri, Jan 27, 2012 at 2:11 AM, Thomas Renninger <trenn@suse.de> wrote:
> > From: Yinghai Lu <yinghai.lu@oracle.com>
> >
> > Fixes PCI device detection on IBM xSeries IBM 3850 M2 / x3950 M2
> > when using ACPI resources (_CRS).
> > This is default, a manual workaround (without this patch)
> > would be pci=nocrs boot param.
> >
> > Tested-by: garyhade@us.ibm.com
> > CC: trenn@suse.de
> > CC: bhelgaas@google.com
> > Signed-off-by: Thomas Renninger <trenn@suse.de>
> > ---
> >  drivers/pci/probe.c |    4 ++++
> >  1 files changed, 4 insertions(+), 0 deletions(-)
> >
> > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> > index 7cc9e2f..1e255c8 100644
> > --- a/drivers/pci/probe.c
> > +++ b/drivers/pci/probe.c
> > @@ -651,6 +651,10 @@ int __devinit pci_scan_bridge(struct pci_bus *bus, struct pci_dev *dev, int max,
> >        dev_dbg(&dev->dev, "scanning [bus %02x-%02x] behind bridge, pass %d\n",
> >                secondary, subordinate, pass);
> >
> > +       /* some bridge primary bus is hard wired to 0 */
> > +       if (!primary && (primary != bus->number) && secondary && subordinate)
> > +               primary = bus->number;
> > +
> >        /* Check if setup is sensible at all */
> >        if (!pass &&
> >            (primary != bus->number || secondary <= bus->number)) {
> > --
> > 1.7.6.1
> >
> 
> I'm not thrilled with adding a machine-specific quirk in this generic
> code path because future rework of this path will always have to
> consider and preserve it.
> 
> I wonder whether it would be possible to set this up so we read
> PCI_PRIMARY_BUS earlier, so we could update that primary bus number in
> a quirk before getting into the rest of pci_scan_bridge().  That might
> take non-trivial rework, since the cached copy of the primary bus
> number is currently in struct pci_bus, not in struct pci_dev.  But
> that in itself is non-intuitive to me: the primary, secondary, and
> subordinate bus numbers are all in struct pci_bus, when they seem more
> like a property of the bridge device than of the bus.
> 
> If we put something like this in mainline, I think it needs a bugzilla
> reference, preferably in bugzilla.kernel.org, where the details (DMI
> info, vendor/device ID of the bridge, etc.) will be public (there is a
> Novell bugzilla, but I don't think it's public).

Thomas or Yinghai, any references for this one just in case someone
wants to clean it up later or get testing for a related change?

Thanks,
-- 
Jesse Barnes, Intel Open Source Technology Center

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