[PATCH] generic 3-level nopmd folding header

Generic headers to fold the 3-level pagetable into 2 levels.
Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/asm-generic/pgtable-nopmd.h

+#ifndef _PGTABLE_NOPMD_H
+#define _PGTABLE_NOPMD_H
+
+#ifndef __ASSEMBLY__
+
+/*
+ * Having the pmd type consist of a pgd gets the size right, and allows
+ * us to conceptually access the pgd entry that this pmd is folded into
+ * without casting.
+ */
+typedef struct { pgd_t pgd; } pmd_t;
+
+#define PMD_SHIFT	PGDIR_SHIFT
+#define PTRS_PER_PMD	1
+#define PMD_SIZE  	(1UL << PMD_SHIFT)
+#define PMD_MASK  	(~(PMD_SIZE-1))
+
+/*
+ * The "pgd_xxx()" functions here are trivial for a folded two-level
+ * setup: the pmd is never bad, and a pmd always exists (as it's folded
+ * into the pgd entry)
+ */
+static inline int pgd_none(pgd_t pgd)		{ return 0; }
+static inline int pgd_bad(pgd_t pgd)		{ return 0; }
+static inline int pgd_present(pgd_t pgd)	{ return 1; }
+static inline void pgd_clear(pgd_t *pgd)	{ }
+#define pmd_ERROR(pmd)				(pgd_ERROR((pmd).pgd))
+
+#define pgd_populate(mm, pmd, pte)		do { } while (0)
+#define pgd_populate_kernel(mm, pmd, pte)	do { } while (0)
+
+/*
+ * (pmds are folded into pgds so this doesn't get actually called,
+ * but the define is needed for a generic inline function.)
+ */
+#define set_pgd(pgdptr, pgdval)			set_pmd((pmd_t *)(pgdptr), (pmd_t) { pgdval })
+
+static inline pmd_t * pmd_offset(pgd_t * pgd, unsigned long address)
+{
+	return (pmd_t *)pgd;
+}
+
+#define pmd_val(x)				(pgd_val((x).pgd))
+#define __pmd(x)				((pmd_t) { __pgd(x) } )
+
+#define pgd_page(pgd)				(pmd_page((pmd_t){ pgd }))
+#define pgd_page_kernel(pgd)			(pmd_page_kernel((pmd_t){ pgd }))
+
+/*
+ * allocating and freeing a pmd is trivial: the 1-entry pmd is
+ * inside the pgd, so has no extra memory associated with it.
+ */
+#define pmd_alloc_one(mm, address)		NULL
+#define pmd_free(x)				do { } while (0)
+#define __pmd_free_tlb(tlb, x)			do { } while (0)
+
+#endif /* __ASSEMBLY__ */
+
+#endif /* _PGTABLE_NOPMD_H */