arm64/mm: Unify CONT_PMD_SHIFT

Similar to how CONT_PTE_SHIFT is determined, this introduces a new
kernel option (CONFIG_CONT_PMD_SHIFT) to determine CONT_PMD_SHIFT.
Signed-off-by: Gavin Shan <gshan@redhat.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20200910095936.20307-3-gshan@redhat.comSigned-off-by: Will Deacon <will@kernel.org>

arch/arm64/Kconfig

@@ -217,6 +217,12 @@ config ARM64_CONT_PTE_SHIFT
 	default 7 if ARM64_16K_PAGES
 	default 4
 
+config ARM64_CONT_PMD_SHIFT
+	int
+	default 5 if ARM64_64K_PAGES
+	default 5 if ARM64_16K_PAGES
+	default 4
+
 config ARCH_MMAP_RND_BITS_MIN
        default 14 if ARM64_64K_PAGES
        default 16 if ARM64_16K_PAGES

arch/arm64/include/asm/pgtable-hwdef.h

@@ -82,17 +82,11 @@
  * Contiguous page definitions.
  */
 #define CONT_PTE_SHIFT		(CONFIG_ARM64_CONT_PTE_SHIFT + PAGE_SHIFT)
-#ifdef CONFIG_ARM64_64K_PAGES
-#define CONT_PMD_SHIFT		(5 + PMD_SHIFT)
-#elif defined(CONFIG_ARM64_16K_PAGES)
-#define CONT_PMD_SHIFT		(5 + PMD_SHIFT)
-#else
-#define CONT_PMD_SHIFT		(4 + PMD_SHIFT)
-#endif
-
 #define CONT_PTES		(1 << (CONT_PTE_SHIFT - PAGE_SHIFT))
 #define CONT_PTE_SIZE		(CONT_PTES * PAGE_SIZE)
 #define CONT_PTE_MASK		(~(CONT_PTE_SIZE - 1))
+
+#define CONT_PMD_SHIFT		(CONFIG_ARM64_CONT_PMD_SHIFT + PMD_SHIFT)
 #define CONT_PMDS		(1 << (CONT_PMD_SHIFT - PMD_SHIFT))
 #define CONT_PMD_SIZE		(CONT_PMDS * PMD_SIZE)
 #define CONT_PMD_MASK		(~(CONT_PMD_SIZE - 1))