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, 1 insertions, 0 deletions

diff --git a/arch/arc/mm/init.c b/arch/arc/mm/init.c
index 46ad9aee7a73..f7ba2a5d5ec8 100644
--- a/arch/arc/mm/init.c
+++ b/arch/arc/mm/init.c
@@ -191,6 +191,7 @@ void __init mem_init(void)
 	highmem_init();
 
 	BUILD_BUG_ON((PTRS_PER_PGD * sizeof(pgd_t)) > PAGE_SIZE);
+	BUILD_BUG_ON((PTRS_PER_PMD * sizeof(pmd_t)) > PAGE_SIZE);
 	BUILD_BUG_ON((PTRS_PER_PTE * sizeof(pte_t)) > PAGE_SIZE);
 }