1 files changed, 143 insertions, 0 deletions

diff --git a/arch/arm/include/asm/pgtable-2level.h b/arch/arm/include/asm/pgtable-2level.h
new file mode 100644
index 000000000000..470457e1cfc5
--- /dev/null
+++ b/arch/arm/include/asm/pgtable-2level.h
@@ -0,0 +1,143 @@
+/*
+ *  arch/arm/include/asm/pgtable-2level.h
+ *
+ *  Copyright (C) 1995-2002 Russell King
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+#ifndef _ASM_PGTABLE_2LEVEL_H
+#define _ASM_PGTABLE_2LEVEL_H
+
+/*
+ * Hardware-wise, we have a two level page table structure, where the first
+ * level has 4096 entries, and the second level has 256 entries.  Each entry
+ * is one 32-bit word.  Most of the bits in the second level entry are used
+ * by hardware, and there aren't any "accessed" and "dirty" bits.
+ *
+ * Linux on the other hand has a three level page table structure, which can
+ * be wrapped to fit a two level page table structure easily - using the PGD
+ * and PTE only.  However, Linux also expects one "PTE" table per page, and
+ * at least a "dirty" bit.
+ *
+ * Therefore, we tweak the implementation slightly - we tell Linux that we
+ * have 2048 entries in the first level, each of which is 8 bytes (iow, two
+ * hardware pointers to the second level.)  The second level contains two
+ * hardware PTE tables arranged contiguously, preceded by Linux versions
+ * which contain the state information Linux needs.  We, therefore, end up
+ * with 512 entries in the "PTE" level.
+ *
+ * This leads to the page tables having the following layout:
+ *
+ *    pgd             pte
+ * |        |
+ * +--------+
+ * |        |       +------------+ +0
+ * +- - - - +       | Linux pt 0 |
+ * |        |       +------------+ +1024
+ * +--------+ +0    | Linux pt 1 |
+ * |        |-----> +------------+ +2048
+ * +- - - - + +4    |  h/w pt 0  |
+ * |        |-----> +------------+ +3072
+ * +--------+ +8    |  h/w pt 1  |
+ * |        |       +------------+ +4096
+ *
+ * See L_PTE_xxx below for definitions of bits in the "Linux pt", and
+ * PTE_xxx for definitions of bits appearing in the "h/w pt".
+ *
+ * PMD_xxx definitions refer to bits in the first level page table.
+ *
+ * The "dirty" bit is emulated by only granting hardware write permission
+ * iff the page is marked "writable" and "dirty" in the Linux PTE.  This
+ * means that a write to a clean page will cause a permission fault, and
+ * the Linux MM layer will mark the page dirty via handle_pte_fault().
+ * For the hardware to notice the permission change, the TLB entry must
+ * be flushed, and ptep_set_access_flags() does that for us.
+ *
+ * The "accessed" or "young" bit is emulated by a similar method; we only
+ * allow accesses to the page if the "young" bit is set.  Accesses to the
+ * page will cause a fault, and handle_pte_fault() will set the young bit
+ * for us as long as the page is marked present in the corresponding Linux
+ * PTE entry.  Again, ptep_set_access_flags() will ensure that the TLB is
+ * up to date.
+ *
+ * However, when the "young" bit is cleared, we deny access to the page
+ * by clearing the hardware PTE.  Currently Linux does not flush the TLB
+ * for us in this case, which means the TLB will retain the transation
+ * until either the TLB entry is evicted under pressure, or a context
+ * switch which changes the user space mapping occurs.
+ */
+#define PTRS_PER_PTE            512
+#define PTRS_PER_PMD            1
+#define PTRS_PER_PGD            2048
+
+#define PTE_HWTABLE_PTRS        (PTRS_PER_PTE)
+#define PTE_HWTABLE_OFF         (PTE_HWTABLE_PTRS * sizeof(pte_t))
+#define PTE_HWTABLE_SIZE        (PTRS_PER_PTE * sizeof(u32))
+
+/*
+ * PMD_SHIFT determines the size of the area a second-level page table can map
+ * PGDIR_SHIFT determines what a third-level page table entry can map
+ */
+#define PMD_SHIFT               21
+#define PGDIR_SHIFT             21
+
+#define PMD_SIZE                (1UL << PMD_SHIFT)
+#define PMD_MASK                (~(PMD_SIZE-1))
+#define PGDIR_SIZE              (1UL << PGDIR_SHIFT)
+#define PGDIR_MASK              (~(PGDIR_SIZE-1))
+
+/*
+ * section address mask and size definitions.
+ */
+#define SECTION_SHIFT           20
+#define SECTION_SIZE            (1UL << SECTION_SHIFT)
+#define SECTION_MASK            (~(SECTION_SIZE-1))
+
+/*
+ * ARMv6 supersection address mask and size definitions.
+ */
+#define SUPERSECTION_SHIFT      24
+#define SUPERSECTION_SIZE       (1UL << SUPERSECTION_SHIFT)
+#define SUPERSECTION_MASK       (~(SUPERSECTION_SIZE-1))
+
+#define USER_PTRS_PER_PGD       (TASK_SIZE / PGDIR_SIZE)
+
+/*
+ * "Linux" PTE definitions.
+ *
+ * We keep two sets of PTEs - the hardware and the linux version.
+ * This allows greater flexibility in the way we map the Linux bits
+ * onto the hardware tables, and allows us to have YOUNG and DIRTY
+ * bits.
+ *
+ * The PTE table pointer refers to the hardware entries; the "Linux"
+ * entries are stored 1024 bytes below.
+ */
+#define L_PTE_PRESENT           (_AT(pteval_t, 1) << 0)
+#define L_PTE_YOUNG             (_AT(pteval_t, 1) << 1)
+#define L_PTE_FILE              (_AT(pteval_t, 1) << 2) /* only when !PRESENT */
+#define L_PTE_DIRTY             (_AT(pteval_t, 1) << 6)
+#define L_PTE_RDONLY            (_AT(pteval_t, 1) << 7)
+#define L_PTE_USER              (_AT(pteval_t, 1) << 8)
+#define L_PTE_XN                (_AT(pteval_t, 1) << 9)
+#define L_PTE_SHARED            (_AT(pteval_t, 1) << 10)        /* shared(v6), coherent(xsc3) */
+
+/*
+ * These are the memory types, defined to be compatible with
+ * pre-ARMv6 CPUs cacheable and bufferable bits:   XXCB
+ */
+#define L_PTE_MT_UNCACHED       (_AT(pteval_t, 0x00) << 2)      /* 0000 */
+#define L_PTE_MT_BUFFERABLE     (_AT(pteval_t, 0x01) << 2)      /* 0001 */
+#define L_PTE_MT_WRITETHROUGH   (_AT(pteval_t, 0x02) << 2)      /* 0010 */
+#define L_PTE_MT_WRITEBACK      (_AT(pteval_t, 0x03) << 2)      /* 0011 */
+#define L_PTE_MT_MINICACHE      (_AT(pteval_t, 0x06) << 2)      /* 0110 (sa1100, xscale) */
+#define L_PTE_MT_WRITEALLOC     (_AT(pteval_t, 0x07) << 2)      /* 0111 */
+#define L_PTE_MT_DEV_SHARED     (_AT(pteval_t, 0x04) << 2)      /* 0100 */
+#define L_PTE_MT_DEV_NONSHARED  (_AT(pteval_t, 0x0c) << 2)      /* 1100 */
+#define L_PTE_MT_DEV_WC         (_AT(pteval_t, 0x09) << 2)      /* 1001 */
+#define L_PTE_MT_DEV_CACHED     (_AT(pteval_t, 0x0b) << 2)      /* 1011 */
+#define L_PTE_MT_MASK           (_AT(pteval_t, 0x0f) << 2)
+
+#endif /* _ASM_PGTABLE_2LEVEL_H */