diff --git a/include/linux/ioport.h b/include/linux/ioport.h
index 9fcaac8..5e3a906 100644
--- a/include/linux/ioport.h
+++ b/include/linux/ioport.h
@@ -51,7 +51,7 @@
 
 #define IORESOURCE_EXCLUSIVE	0x08000000	/* Userland may not map this resource */
 #define IORESOURCE_DISABLED	0x10000000
-#define IORESOURCE_UNSET	0x20000000
+#define IORESOURCE_UNSET	0x20000000	/* No address assigned yet */
 #define IORESOURCE_AUTO		0x40000000
 #define IORESOURCE_BUSY		0x80000000	/* Driver has marked this resource busy */