1 files changed, 16 insertions, 3 deletions

diff --git a/arch/arm/kernel/bios32.c b/arch/arm/kernel/bios32.c
index e17dd2591b26..d22e35168e88 100644
--- a/arch/arm/kernel/bios32.c
+++ b/arch/arm/kernel/bios32.c
@@ -374,16 +374,29 @@ EXPORT_SYMBOL(pcibios_fixup_bus);
 #endif
 
 /*
- * Swizzle the device pin each time we cross a bridge.
- * This might update pin and returns the slot number.
+ * Swizzle the device pin each time we cross a bridge.  If a platform does
+ * not provide a swizzle function, we perform the standard PCI swizzling.
+ *
+ * The default swizzling walks up the bus tree one level at a time, applying
+ * the standard swizzle function at each step, stopping when it finds the PCI
+ * root bus.  This will return the slot number of the bridge device on the
+ * root bus and the interrupt pin on that device which should correspond
+ * with the downstream device interrupt.
+ *
+ * Platforms may override this, in which case the slot and pin returned
+ * depend entirely on the platform code.  However, please note that the
+ * PCI standard swizzle is implemented on plug-in cards and Cardbus based
+ * PCI extenders, so it can not be ignored.
  */
 static u8 __devinit pcibios_swizzle(struct pci_dev *dev, u8 *pin)
 {
         struct pci_sys_data *sys = dev->sysdata;
-        int slot = 0, oldpin = *pin;
+        int slot, oldpin = *pin;
 
         if (sys->swizzle)
                 slot = sys->swizzle(dev, pin);
+        else
+                slot = pci_common_swizzle(dev, pin);
 
         if (debug_pci)
                 printk("PCI: %s swizzling pin %d => pin %d slot %d\n",