--- zzzz-none-000/linux-4.1.52/include/linux/pfn.h	2018-05-28 02:26:45.000000000 +0000
+++ bcm63-7530ax-731/linux-4.1.52/include/linux/pfn.h	2022-03-02 11:37:13.000000000 +0000
@@ -9,5 +9,11 @@
 #define PFN_UP(x)	(((x) + PAGE_SIZE-1) >> PAGE_SHIFT)
 #define PFN_DOWN(x)	((x) >> PAGE_SHIFT)
 #define PFN_PHYS(x)	((phys_addr_t)(x) << PAGE_SHIFT)
+#if defined(CONFIG_BCM_KF_MISC_BACKPORTS)
+/* this definition is missing in 4.1.y, needs to be brought
+   from master branch
+*/
+#define PHYS_PFN(x)    ((unsigned long)((x) >> PAGE_SHIFT))
+#endif
 
 #endif