ARC: mm: Introduce explicit super page size support
MMUv4 supports 2 concurrent page sizes: Normal and Super [4K to 16M]
So far Linux supported a single super page size for a given Normal page,
depending on the software page walking address split.
e.g. we had 11:8:13 address split for 8K page, which meant super page
was 2 ^(8+13) = 2M (given that THP size has to be PMD_SHIFT)
Now we turn this around, by allowing multiple Super Pages in Kconfig
(currently 2M and 16M only) and forcing page walker address split to
PGDIR_SHIFT and PAGE_SHIFT
For configs without Super page, things are same as before and
PGDIR_SHIFT can be hacked to get non default address split
The motivation for this change is a customer who needs 16M super page
and a 8K Normal page combo.
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
diff --git a/arch/arc/include/asm/pgtable.h b/arch/arc/include/asm/pgtable.h
index 57af2f0..d426d42 100644
--- a/arch/arc/include/asm/pgtable.h
+++ b/arch/arc/include/asm/pgtable.h
@@ -179,37 +179,44 @@
#define __S111 PAGE_U_X_W_R
/****************************************************************
- * Page Table Lookup split
+ * 2 tier (PGD:PTE) software page walker
*
- * We implement 2 tier paging and since this is all software, we are free
- * to customize the span of a PGD / PTE entry to suit us
- *
- * 32 bit virtual address
+ * [31] 32 bit virtual address [0]
* -------------------------------------------------------
- * | BITS_FOR_PGD | BITS_FOR_PTE | BITS_IN_PAGE |
+ * | | <------------ PGDIR_SHIFT ----------> |
+ * | | |
+ * | BITS_FOR_PGD | BITS_FOR_PTE | <-- PAGE_SHIFT --> |
* -------------------------------------------------------
* | | |
* | | --> off in page frame
- * | |
* | ---> index into Page Table
- * |
* ----> index into Page Directory
+ *
+ * In a single page size configuration, only PAGE_SHIFT is fixed
+ * So both PGD and PTE sizing can be tweaked
+ * e.g. 8K page (PAGE_SHIFT 13) can have
+ * - PGDIR_SHIFT 21 -> 11:8:13 address split
+ * - PGDIR_SHIFT 24 -> 8:11:13 address split
+ *
+ * If Super Page is configured, PGDIR_SHIFT becomes fixed too,
+ * so the sizing flexibility is gone.
*/
-#define BITS_IN_PAGE PAGE_SHIFT
-
-/* Optimal Sizing of Pg Tbl - based on MMU page size */
-#if defined(CONFIG_ARC_PAGE_SIZE_8K)
-#define BITS_FOR_PTE 8 /* 11:8:13 */
-#elif defined(CONFIG_ARC_PAGE_SIZE_16K)
-#define BITS_FOR_PTE 8 /* 10:8:14 */
-#elif defined(CONFIG_ARC_PAGE_SIZE_4K)
-#define BITS_FOR_PTE 9 /* 11:9:12 */
+#if defined(CONFIG_ARC_HUGEPAGE_16M)
+#define PGDIR_SHIFT 24
+#elif defined(CONFIG_ARC_HUGEPAGE_2M)
+#define PGDIR_SHIFT 21
+#else
+/*
+ * Only Normal page support so "hackable" (see comment above)
+ * Default value provides 11:8:13 (8K), 11:9:12 (4K)
+ */
+#define PGDIR_SHIFT 21
#endif
-#define BITS_FOR_PGD (32 - BITS_FOR_PTE - BITS_IN_PAGE)
+#define BITS_FOR_PTE (PGDIR_SHIFT - PAGE_SHIFT)
+#define BITS_FOR_PGD (32 - PGDIR_SHIFT)
-#define PGDIR_SHIFT (32 - BITS_FOR_PGD)
#define PGDIR_SIZE (1UL << PGDIR_SHIFT) /* vaddr span, not PDG sz */
#define PGDIR_MASK (~(PGDIR_SIZE-1))