ARC: mm: support 3 levels of page tables

ARCv2 MMU is software walked and Linux implements 2 levels of paging: pgd/pte.
Forthcoming hw will have multiple levels, so this change preps mm code
for same. It is also fun to try multi levels even on soft-walked code to
ensure generic mm code is robust to handle.

overview
________

2 levels {pgd, pte} : pmd is folded but pmd_* macros are valid and operate on pgd
3 levels {pgd, pmd, pte}:
  - pud is folded and pud_* macros point to pgd
  - pmd_* macros operate on actual pmd

code changes
____________

1. #include <asm-generic/pgtable-nopud.h>

2. Define CONFIG_PGTABLE_LEVELS 3

3a. Define PMD_SHIFT, PMD_SIZE, PMD_MASK, pmd_t
3b. Define pmd_val() which actually deals with pmd
    (pmd_offset(), pmd_index() are provided by generic code)
3c. pmd_alloc_one()/pmd_free() also provided by generic code
    (pmd_populate/pmd_free already exist)

4. Define pud_none(), pud_bad() macros based on generic pud_val() which
   internally pertains to pgd now.
4b. define pud_populate() to just setup pgd

Acked-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Vineet Gupta <vgupta@kernel.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/arch/arc/include/asm/page.h b/arch/arc/include/asm/page.h
index 28ed82b1800f..5d7899d87c08 100644
--- a/arch/arc/include/asm/page.h
+++ b/arch/arc/include/asm/page.h
@@ -41,6 +41,17 @@ typedef struct {
 #define pgd_val(x)	((x).pgd)
 #define __pgd(x)	((pgd_t) { (x) })
 
+#if CONFIG_PGTABLE_LEVELS > 2
+
+typedef struct {
+	unsigned long pmd;
+} pmd_t;
+
+#define pmd_val(x)	((x).pmd)
+#define __pmd(x)	((pmd_t) { (x) })
+
+#endif
+
 typedef struct {
 #ifdef CONFIG_ARC_HAS_PAE40
 	unsigned long long pte;