diff --git a/arch/x86/kernel/amd_iommu.c b/arch/x86/kernel/amd_iommu.c
index dec10e1a397c2fa9dac7c6890846acdf42af76e6..8c3deb027d3acf66408732bb998a62c7a0eb9f48 100644
--- a/arch/x86/kernel/amd_iommu.c
+++ b/arch/x86/kernel/amd_iommu.c
@@ -664,7 +664,7 @@ static int get_device_resources(struct device *dev,
 	BUG_ON(!dev || dev->bus != &pci_bus_type || !dev->dma_mask);
 
 	pcidev = to_pci_dev(dev);
-	_bdf = (pcidev->bus->number << 8) | pcidev->devfn;
+	_bdf = calc_devid(pcidev->bus->number, pcidev->devfn);
 
 	/* device not translated by any IOMMU in the system? */
 	if (_bdf >= amd_iommu_last_bdf) {
diff --git a/arch/x86/kernel/amd_iommu_init.c b/arch/x86/kernel/amd_iommu_init.c
index e0ff9404e6c94bd7e4fbd24f41bbd2ae65db1168..9bf1b8111b08b042b8b259431e454e120ccfd244 100644
--- a/arch/x86/kernel/amd_iommu_init.c
+++ b/arch/x86/kernel/amd_iommu_init.c
@@ -30,7 +30,6 @@
 /*
  * definitions for the ACPI scanning code
  */
-#define DEVID(bus, devfn) (((bus) << 8) | (devfn))
 #define PCI_BUS(x) (((x) >> 8) & 0xff)
 #define IVRS_HEADER_LENGTH 48
 
@@ -295,7 +294,7 @@ static int __init find_last_devid_on_pci(int bus, int dev, int fn, int cap_ptr)
 	u32 cap;
 
 	cap = read_pci_config(bus, dev, fn, cap_ptr+MMIO_RANGE_OFFSET);
-	update_last_devid(DEVID(MMIO_GET_BUS(cap), MMIO_GET_LD(cap)));
+	update_last_devid(calc_devid(MMIO_GET_BUS(cap), MMIO_GET_LD(cap)));
 
 	return 0;
 }
@@ -494,8 +493,10 @@ static void __init init_iommu_from_pci(struct amd_iommu *iommu)
 	iommu->cap = read_pci_config(bus, dev, fn, cap_ptr+MMIO_CAP_HDR_OFFSET);
 
 	range = read_pci_config(bus, dev, fn, cap_ptr+MMIO_RANGE_OFFSET);
-	iommu->first_device = DEVID(MMIO_GET_BUS(range), MMIO_GET_FD(range));
-	iommu->last_device = DEVID(MMIO_GET_BUS(range), MMIO_GET_LD(range));
+	iommu->first_device = calc_devid(MMIO_GET_BUS(range),
+					 MMIO_GET_FD(range));
+	iommu->last_device = calc_devid(MMIO_GET_BUS(range),
+					MMIO_GET_LD(range));
 }
 
 /*
diff --git a/include/asm-x86/amd_iommu_types.h b/include/asm-x86/amd_iommu_types.h
index 2e8601b0f006367fb88d67a6e68b0a6bc6c7d925..22aa58ca1991c3003565f8fbc0313f3cf37b9d92 100644
--- a/include/asm-x86/amd_iommu_types.h
+++ b/include/asm-x86/amd_iommu_types.h
@@ -332,4 +332,11 @@ static inline void print_devid(u16 devid, int nl)
 		printk("\n");
 }
 
+/* takes bus and device/function and returns the device id
+ * FIXME: should that be in generic PCI code? */
+static inline u16 calc_devid(u8 bus, u8 devfn)
+{
+	return (((u16)bus) << 8) | devfn;
+}
+
 #endif