On Wed, 25 Jan 2023 21:07:57 +0200 Mike Rapoport [off-list ref] wrote:

Every architecture that supports FLATMEM memory model defines its own
version of pfn_valid() that essentially compares a pfn to max_mapnr.

Use mips/powerpc version implemented as static inline as a generic
implementation of pfn_valid() and drop its per-architecture definitions

arm allnoconfig:

./include/asm-generic/memory_model.h:23:19: error: static declaration of 'pfn_valid' follows non-static declaration
   23 | static inline int pfn_valid(unsigned long pfn)
      |                   ^~~~~~~~~
./arch/arm/include/asm/page.h:160:12: note: previous declaration of 'pfn_valid' with type 'int(long unsigned int)'
  160 | extern int pfn_valid(unsigned long);
      |            ^~~~~~~~~


I thought of doing

--- a/arch/arm/include/asm/page.h~mm-arch-add-generic-implementation-of-pfn_valid-for-flatmem-fix
+++ a/arch/arm/include/asm/page.h

@@ -156,10 +156,6 @@ extern void copy_page(void *to, const vo
 
 typedef struct page *pgtable_t;
 
-#ifdef CONFIG_HAVE_ARCH_PFN_VALID
-extern int pfn_valid(unsigned long);
-#endif
-
 #include <asm/memory.h>
 
 #endif /* !__ASSEMBLY__ */

_

but I'm seeing a pfn_valid declaration in arch/arc/include/asm/page.h
which might be a problem.

v2, please ;)