diff --git a/Documentation/filesystems/sysfs-pci.txt b/Documentation/filesystems/sysfs-pci.txt
index 6ea1ced..25b7f1c 100644
--- a/Documentation/filesystems/sysfs-pci.txt
+++ b/Documentation/filesystems/sysfs-pci.txt
@@ -117,6 +117,10 @@ code must define HAVE_PCI_MMAP and provide a pci_mmap_page_range function.
 Platforms are free to only support subsets of the mmap functionality, but
 useful return codes should be provided.
 
+Platforms which support write-combining maps of PCI resources must define
+arch_can_pci_mmap_wc() which shall evaluate to non-zero at runtime when
+write-combining is permitted.
+
 Legacy resources are protected by the HAVE_PCI_LEGACY define.  Platforms
 wishing to support legacy functionality should define it and provide
 pci_legacy_read, pci_legacy_write and pci_mmap_legacy_page_range functions.
diff --git a/arch/arm64/include/asm/pci.h b/arch/arm64/include/asm/pci.h
index f73734f..53b1541 100644
--- a/arch/arm64/include/asm/pci.h
+++ b/arch/arm64/include/asm/pci.h
@@ -38,6 +38,7 @@ static inline int pci_proc_domain(struct pci_bus *bus)
 #endif  /* CONFIG_PCI */
 
 #define HAVE_PCI_MMAP
+#define arch_can_pci_mmap_wc()	1
 extern int pci_mmap_page_range(struct pci_dev *dev, struct vm_area_struct *vma,
 			       enum pci_mmap_state mmap_state, int write_combine);
 
diff --git a/arch/ia64/include/asm/pci.h b/arch/ia64/include/asm/pci.h
index c0835b0..6283758 100644
--- a/arch/ia64/include/asm/pci.h
+++ b/arch/ia64/include/asm/pci.h
@@ -51,6 +51,8 @@ extern unsigned long ia64_max_iommu_merge_mask;
 #define PCI_DMA_BUS_IS_PHYS	(ia64_max_iommu_merge_mask == ~0UL)
 
 #define HAVE_PCI_MMAP
+#define arch_can_pci_mmap_wc()	1
+
 extern int pci_mmap_page_range (struct pci_dev *dev, struct vm_area_struct *vma,
 				enum pci_mmap_state mmap_state, int write_combine);
 #define HAVE_PCI_LEGACY
diff --git a/arch/powerpc/include/asm/pci.h b/arch/powerpc/include/asm/pci.h
index 93eded8..b5b68c6 100644
--- a/arch/powerpc/include/asm/pci.h
+++ b/arch/powerpc/include/asm/pci.h
@@ -81,8 +81,9 @@ struct vm_area_struct;
 int pci_mmap_page_range(struct pci_dev *pdev, struct vm_area_struct *vma,
 			enum pci_mmap_state mmap_state, int write_combine);
 
-/* Tell drivers/pci/proc.c that we have pci_mmap_page_range() */
-#define HAVE_PCI_MMAP	1
+/* Tell drivers/pci/proc.c that we have pci_mmap_page_range() and it does WC */
+#define HAVE_PCI_MMAP		1
+#define arch_can_pci_mmap_wc()	1
 
 extern int pci_legacy_read(struct pci_bus *bus, loff_t port, u32 *val,
 			   size_t count);
diff --git a/arch/x86/include/asm/pci.h b/arch/x86/include/asm/pci.h
index 1411dbe..f6e22c2 100644
--- a/arch/x86/include/asm/pci.h
+++ b/arch/x86/include/asm/pci.h
@@ -7,6 +7,7 @@
 #include <linux/string.h>
 #include <linux/scatterlist.h>
 #include <asm/io.h>
+#include <asm/pat.h>
 #include <asm/x86_init.h>
 
 #ifdef __KERNEL__
@@ -102,6 +103,7 @@ int pcibios_set_irq_routing(struct pci_dev *dev, int pin, int irq);
 
 
 #define HAVE_PCI_MMAP
+#define arch_can_pci_mmap_wc()	pat_enabled()
 extern int pci_mmap_page_range(struct pci_dev *dev, struct vm_area_struct *vma,
 			       enum pci_mmap_state mmap_state,
 			       int write_combine);
diff --git a/arch/xtensa/include/asm/pci.h b/arch/xtensa/include/asm/pci.h
index 5d6bd93..f106879 100644
--- a/arch/xtensa/include/asm/pci.h
+++ b/arch/xtensa/include/asm/pci.h
@@ -51,7 +51,11 @@ int pci_mmap_page_range(struct pci_dev *pdev, struct vm_area_struct *vma,
 			enum pci_mmap_state mmap_state, int write_combine);
 
 /* Tell drivers/pci/proc.c that we have pci_mmap_page_range() */
-#define HAVE_PCI_MMAP	1
+#define HAVE_PCI_MMAP		1
+
+/* This was wrapped in #if 0 since the first merge of xtensa support...
+#define arch_can_pci_mmap_wc()	1
+*/
 
 #endif /* __KERNEL__ */
 
diff --git a/arch/xtensa/kernel/pci.c b/arch/xtensa/kernel/pci.c
index b848cc3..c5944d3 100644
--- a/arch/xtensa/kernel/pci.c
+++ b/arch/xtensa/kernel/pci.c
@@ -345,7 +345,7 @@ __pci_mmap_set_pgprot(struct pci_dev *dev, struct vm_area_struct *vma,
 
 	/* Set to write-through */
 	prot = (prot & _PAGE_CA_MASK) | _PAGE_CA_WT;
-#if 0
+#ifdef arch_can_pci_mmap_wc
 	if (!write_combine)
 		prot |= _PAGE_WRITETHRU;
 #endif
diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index 25d010d..e0474f3 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -1206,10 +1206,12 @@ static int pci_create_resource_files(struct pci_dev *pdev)
 			continue;
 
 		retval = pci_create_attr(pdev, i, 0);
+#ifdef arch_can_pci_mmap_wc
 		/* for prefetchable resources, create a WC mappable file */
-		if (!retval && pdev->resource[i].flags & IORESOURCE_PREFETCH)
+		if (!retval && arch_can_pci_mmap_wc() &&
+		    pdev->resource[i].flags & IORESOURCE_PREFETCH)
 			retval = pci_create_attr(pdev, i, 1);
-
+#endif
 		if (retval) {
 			pci_remove_resource_files(pdev);
 			return retval;
diff --git a/drivers/pci/proc.c b/drivers/pci/proc.c
index f82710a..5cd960c 100644
--- a/drivers/pci/proc.c
+++ b/drivers/pci/proc.c
@@ -209,15 +209,18 @@ static long proc_bus_pci_ioctl(struct file *file, unsigned int cmd,
 		fpriv->mmap_state = pci_mmap_mem;
 		break;
 
+#ifdef arch_can_pci_mmap_wc
 	case PCIIOC_WRITE_COMBINE:
-		if (arg)
-			fpriv->write_combine = 1;
-		else
-			fpriv->write_combine = 0;
-		break;
-
+		if (arch_can_pci_mmap_wc()) {
+			if (arg)
+				fpriv->write_combine = 1;
+			else
+				fpriv->write_combine = 0;
+			break;
+		}
+		/* If arch decided it can't, fall through... */
+#endif /* arch_can_pci_mmap_wc */
 #endif /* HAVE_PCI_MMAP */
-
 	default:
 		ret = -EINVAL;
 		break;
