diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 265a32e1ff74c6f9f5ab87a538044749ec3b7b1d..7da43337ad2337cf54f68acfa007038b7b28dbc3 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1445,6 +1445,17 @@ static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn)
 #endif
 
 #ifndef CONFIG_HAVE_ARCH_PFN_VALID
+/**
+ * pfn_valid - check if there is a valid memory map entry for a PFN
+ * @pfn: the page frame number to check
+ *
+ * Check if there is a valid memory map entry aka struct page for the @pfn.
+ * Note, that availability of the memory map entry does not imply that
+ * there is actual usable memory at that @pfn. The struct page may
+ * represent a hole or an unusable page frame.
+ *
+ * Return: 1 for PFNs that have memory map entries and 0 otherwise
+ */
 static inline int pfn_valid(unsigned long pfn)
 {
 	struct mem_section *ms;