1 files changed, 22 insertions, 0 deletions

diff --git a/include/linux/io.h b/include/linux/io.h
index e2c8419278c1..82ef36eac8a1 100644
--- a/include/linux/io.h
+++ b/include/linux/io.h
@@ -141,4 +141,26 @@ enum {
 void *memremap(resource_size_t offset, size_t size, unsigned long flags);
 void memunmap(void *addr);
 
+/*
+ * On x86 PAT systems we have memory tracking that keeps track of
+ * the allowed mappings on memory ranges. This tracking works for
+ * all the in-kernel mapping APIs (ioremap*), but where the user
+ * wishes to map a range from a physical device into user memory
+ * the tracking won't be updated. This API is to be used by
+ * drivers which remap physical device pages into userspace,
+ * and wants to make sure they are mapped WC and not UC.
+ */
+#ifndef arch_io_reserve_memtype_wc
+static inline int arch_io_reserve_memtype_wc(resource_size_t base,
+                                             resource_size_t size)
+{
+        return 0;
+}
+
+static inline void arch_io_free_memtype_wc(resource_size_t base,
+                                           resource_size_t size)
+{
+}
+#endif
+
 #endif /* _LINUX_IO_H */