PCI: workaround hard-wired bus number V2

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.

V2: Add dev_warn if the workaround is hit. This should reveal
how common such setups are (via google) and point to possible
problems if things are still not working as expected.
-> Suggested by Jan Beulich.

Cc: stable@vger.kernel.org
Tested-by: garyhade@us.ibm.com
Signed-off-by: Yinghai Lu <yinghai.lu@oracle.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 7cc9e2f0f47c..71eac9cd724d 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -651,6 +651,11 @@ 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);
 
+        if (!primary && (primary != bus->number) && secondary && subordinate) {
+                dev_warn(&dev->dev, "Primary bus is hard wired to 0\n");
+                primary = bus->number;
+        }
+
         /* Check if setup is sensible at all */
         if (!pass &&
             (primary != bus->number || secondary <= bus->number)) {