3 files changed, 79 insertions, 2 deletions
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 88821fa26f19..bfb64d672e19 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -15,6 +15,7 @@
 #include <linux/backing-dev-defs.h>
 #include <linux/wait.h>
 #include <linux/mempool.h>
+#include <linux/pfn.h>
 #include <linux/bio.h>
 #include <linux/stringify.h>
 #include <linux/gfp.h>
@@ -1628,7 +1629,7 @@ struct blk_dax_ctl {
 	sector_t sector;
 	void __pmem *addr;
 	long size;
-	unsigned long pfn;
+	pfn_t pfn;
 };
 
 struct block_device_operations {
@@ -1638,7 +1639,7 @@ struct block_device_operations {
 	int (*ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
 	int (*compat_ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
 	long (*direct_access)(struct block_device *, sector_t, void __pmem **,
-			unsigned long *pfn);
+			pfn_t *);
 	unsigned int (*check_events) (struct gendisk *disk,
 				      unsigned int clearing);
 	/* ->media_changed() is DEPRECATED, use ->check_events() instead */
diff --git a/include/linux/pfn.h b/include/linux/pfn.h
index 97f3e88aead4..2d8e49711b63 100644
--- a/include/linux/pfn.h
+++ b/include/linux/pfn.h
@@ -3,6 +3,15 @@
 
 #ifndef __ASSEMBLY__
 #include <linux/types.h>
+
+/*
+ * pfn_t: encapsulates a page-frame number that is optionally backed
+ * by memmap (struct page).  Whether a pfn_t has a 'struct page'
+ * backing is indicated by flags in the high bits of the value.
+ */
+typedef struct {
+	unsigned long val;
+} pfn_t;
 #endif
 
 #define PFN_ALIGN(x)	(((unsigned long)(x) + (PAGE_SIZE - 1)) & PAGE_MASK)
diff --git a/include/linux/pfn_t.h b/include/linux/pfn_t.h
new file mode 100644
index 000000000000..c557a0e0b20c
--- /dev/null
+++ b/include/linux/pfn_t.h
@@ -0,0 +1,67 @@
+#ifndef _LINUX_PFN_T_H_
+#define _LINUX_PFN_T_H_
+#include <linux/mm.h>
+
+/*
+ * PFN_FLAGS_MASK - mask of all the possible valid pfn_t flags
+ * PFN_SG_CHAIN - pfn is a pointer to the next scatterlist entry
+ * PFN_SG_LAST - pfn references a page and is the last scatterlist entry
+ * PFN_DEV - pfn is not covered by system memmap by default
+ * PFN_MAP - pfn has a dynamic page mapping established by a device driver
+ */
+#define PFN_FLAGS_MASK (((unsigned long) ~PAGE_MASK) \
+		<< (BITS_PER_LONG - PAGE_SHIFT))
+#define PFN_SG_CHAIN (1UL << (BITS_PER_LONG - 1))
+#define PFN_SG_LAST (1UL << (BITS_PER_LONG - 2))
+#define PFN_DEV (1UL << (BITS_PER_LONG - 3))
+#define PFN_MAP (1UL << (BITS_PER_LONG - 4))
+
+static inline pfn_t __pfn_to_pfn_t(unsigned long pfn, unsigned long flags)
+{
+	pfn_t pfn_t = { .val = pfn | (flags & PFN_FLAGS_MASK), };
+
+	return pfn_t;
+}
+
+/* a default pfn to pfn_t conversion assumes that @pfn is pfn_valid() */
+static inline pfn_t pfn_to_pfn_t(unsigned long pfn)
+{
+	return __pfn_to_pfn_t(pfn, 0);
+}
+
+extern pfn_t phys_to_pfn_t(dma_addr_t addr, unsigned long flags);
+
+static inline bool pfn_t_has_page(pfn_t pfn)
+{
+	return (pfn.val & PFN_MAP) == PFN_MAP || (pfn.val & PFN_DEV) == 0;
+}
+
+static inline unsigned long pfn_t_to_pfn(pfn_t pfn)
+{
+	return pfn.val & ~PFN_FLAGS_MASK;
+}
+
+static inline struct page *pfn_t_to_page(pfn_t pfn)
+{
+	if (pfn_t_has_page(pfn))
+		return pfn_to_page(pfn_t_to_pfn(pfn));
+	return NULL;
+}
+
+static inline dma_addr_t pfn_t_to_phys(pfn_t pfn)
+{
+	return PFN_PHYS(pfn_t_to_pfn(pfn));
+}
+
+static inline void *pfn_t_to_virt(pfn_t pfn)
+{
+	if (pfn_t_has_page(pfn))
+		return __va(pfn_t_to_phys(pfn));
+	return NULL;
+}
+
+static inline pfn_t page_to_pfn_t(struct page *page)
+{
+	return pfn_to_pfn_t(page_to_pfn(page));
+}
+#endif /* _LINUX_PFN_T_H_ */