[PATCH v2] [RFC] ARM: modify pgd_t definition for TRANSPARENT_HUGEPAGE_PUD

[Arnd Bergmann]

I ran into build errors on ARM after Willy's newly added generic
TRANSPARENT_HUGEPAGE_PUD support. We don't support this feature
on ARM at all, but the patch causes a build error anyway:

In file included from ../kernel/memremap.c:17:0:
../include/linux/pfn_t.h:108:7: error: 'pud_mkdevmap' declared as function returning an array
 pud_t pud_mkdevmap(pud_t pud);

We don't use a PUD on ARM, so pud_t is defined as pmd_t, which
in turn is defined as

typedef unsigned long pgd_t[2];

on NOMMU and on 2-level MMU configurations. There is an (unused)
other definition using a struct around the array, which happens to
work fine here.

There is a comment in the file about the fact the other version
is "easier on the compiler", and I've traced that version back
to linux-2.1.80 when ARM support was first merged back in 1998.

It's probably a safe assumption that this is no longer necessary:
The same logic existed in asm-i386 at the time but was removed
a year later in 2.3.23pre3. The STRICT_MM_TYPECHECKS logic
also ended up getting copied into other architectures, which
use them in various ways:

* both defined, but using strict:
arch/alpha/include/asm/page.h:#define STRICT_MM_TYPECHECKS
arch/sparc/include/asm/page_64.h:#define STRICT_MM_TYPECHECKS
arch/ia64/include/asm/page.h:#  define STRICT_MM_TYPECHECKS
arch/parisc/include/asm/page.h:#define STRICT_MM_TYPECHECKS

* both defined, but using non-strict:
arch/arc/include/asm/page.h:#undef STRICT_MM_TYPECHECKS
arch/arm/include/asm/pgtable-2level-types.h:#undef STRICT_MM_TYPECHECKS
arch/arm/include/asm/pgtable-3level-types.h:#undef STRICT_MM_TYPECHECKS
arch/arm64/include/asm/pgtable-types.h:#undef STRICT_MM_TYPECHECKS
arch/sparc/include/asm/page_32.h:/* #define STRICT_MM_TYPECHECKS */
arch/unicore32/include/asm/page.h:#undef STRICT_MM_TYPECHECKS

* Kconfig option:
arch/powerpc/Kconfig.debug:config STRICT_MM_TYPECHECKS
			 	default n

Everthing else uses only the strict definitions.

For the moment, this only does the minimal change to fix things
on ARM in linux-next. At least in case of sparc32, passing structs
to functions is traditionally inefficient and the non-strict version
should be kept, whether we change any of the other architectures
depends on further testing.

Signed-off-by: Arnd Bergmann <arnd at arndb.de>
Fixes: a27da20ed50e ("mm: add support for PUD-sized transparent hugepages")
Link: http://www.spinics.net/lists/linux-mm/msg101404.html
---
 arch/arm/include/asm/page-nommu.h           | 4 ++--
 arch/arm/include/asm/pgtable-2level-types.h | 7 +++----
 2 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/arch/arm/include/asm/page-nommu.h b/arch/arm/include/asm/page-nommu.h
index d1b162a18dcb..3db1ca22fecb 100644
--- a/arch/arm/include/asm/page-nommu.h
+++ b/arch/arm/include/asm/page-nommu.h
@@ -31,12 +31,12 @@
  */
 typedef unsigned long pte_t;
 typedef unsigned long pmd_t;
-typedef unsigned long pgd_t[2];
+typedef struct { unsigned long pgd[2]; } pgd_t;
 typedef unsigned long pgprot_t;
 
 #define pte_val(x)      (x)
 #define pmd_val(x)      (x)
-#define pgd_val(x)	((x)[0])
+#define pgd_val(x)	((x).pgd[0])
 #define pgprot_val(x)   (x)
 
 #define __pte(x)        (x)
diff --git a/arch/arm/include/asm/pgtable-2level-types.h b/arch/arm/include/asm/pgtable-2level-types.h
index 66cb5b0e89c5..9b9815d5ebd6 100644
--- a/arch/arm/include/asm/pgtable-2level-types.h
+++ b/arch/arm/include/asm/pgtable-2level-types.h
@@ -24,6 +24,9 @@
 typedef u32 pteval_t;
 typedef u32 pmdval_t;
 
+typedef struct { pmdval_t pgd[2]; } pgd_t;
+#define pgd_val(x)	((x).pgd[0])
+
 #undef STRICT_MM_TYPECHECKS
 
 #ifdef STRICT_MM_TYPECHECKS
@@ -32,12 +35,10 @@ typedef u32 pmdval_t;
  */
 typedef struct { pteval_t pte; } pte_t;
 typedef struct { pmdval_t pmd; } pmd_t;
-typedef struct { pmdval_t pgd[2]; } pgd_t;
 typedef struct { pteval_t pgprot; } pgprot_t;
 
 #define pte_val(x)      ((x).pte)
 #define pmd_val(x)      ((x).pmd)
-#define pgd_val(x)	((x).pgd[0])
 #define pgprot_val(x)   ((x).pgprot)
 
 #define __pte(x)        ((pte_t) { (x) } )
@@ -50,12 +51,10 @@ typedef struct { pteval_t pgprot; } pgprot_t;
  */
 typedef pteval_t pte_t;
 typedef pmdval_t pmd_t;
-typedef pmdval_t pgd_t[2];
 typedef pteval_t pgprot_t;
 
 #define pte_val(x)      (x)
 #define pmd_val(x)      (x)
-#define pgd_val(x)	((x)[0])
 #define pgprot_val(x)   (x)
 
 #define __pte(x)        (x)
-- 
2.7.0