build_mem_type_table

1.函数调用关系

start_kernel
    -->setup_arch
        -->paging_init
            -->build_mem_type_table

2.全局变量

在arch/arm/mm/mmu.c中定义以下全局变量

2.1 int cachepolicy

static unsigned int cachepolicy __initdata = CPOLICY_WRITEBACK;

指定缓冲策略，可选值如下宏定义

#define CPOLICY_UNCACHED    0
#define CPOLICY_BUFFERED    1
#define CPOLICY_WRITETHROUGH    2
#define CPOLICY_WRITEBACK    3
#define CPOLICY_WRITEALLOC    4

2.2 struct cachepolicy cache_policies[]

static struct cachepolicy cache_policies[] __initdata = {
    {
        .policy        = "uncached",
        .cr_mask    = CR_W|CR_C,
        .pmd        = PMD_SECT_UNCACHED,
        .pte        = L_PTE_MT_UNCACHED,
    }, {
        .policy        = "buffered",
        .cr_mask    = CR_C,
        .pmd        = PMD_SECT_BUFFERED,
        .pte        = L_PTE_MT_BUFFERABLE,
    }, {
        .policy        = "writethrough",
        .cr_mask    = 0,
        .pmd        = PMD_SECT_WT,
        .pte        = L_PTE_MT_WRITETHROUGH,
    }, {
        .policy        = "writeback",
        .cr_mask    = 0,
        .pmd        = PMD_SECT_WB,
        .pte        = L_PTE_MT_WRITEBACK,
    }, {
        .policy        = "writealloc",
        .cr_mask    = 0,
        .pmd        = PMD_SECT_WBWA,
        .pte        = L_PTE_MT_WRITEALLOC,
    }
};

 2.3 struct mem_type mem_types[]

struct mem_type {
    unsigned int prot_pte;
    unsigned int prot_l1;
    unsigned int prot_sect;
    unsigned int domain;
};

static struct mem_type mem_types[] = {
    [MT_DEVICE] = {          /* Strongly ordered / ARMv6 shared device */
        .prot_pte    = PROT_PTE_DEVICE | L_PTE_MT_DEV_SHARED |
                  L_PTE_SHARED,
        .prot_l1    = PMD_TYPE_TABLE,
        .prot_sect    = PROT_SECT_DEVICE | PMD_SECT_S,
        .domain        = DOMAIN_IO,
    },
    [MT_DEVICE_NONSHARED] = { /* ARMv6 non-shared device */
        .prot_pte    = PROT_PTE_DEVICE | L_PTE_MT_DEV_NONSHARED,
        .prot_l1    = PMD_TYPE_TABLE,
        .prot_sect    = PROT_SECT_DEVICE,
        .domain        = DOMAIN_IO,
    },
    [MT_DEVICE_CACHED] = {      /* ioremap_cached */
        .prot_pte    = PROT_PTE_DEVICE | L_PTE_MT_DEV_CACHED,
        .prot_l1    = PMD_TYPE_TABLE,
        .prot_sect    = PROT_SECT_DEVICE | PMD_SECT_WB,
        .domain        = DOMAIN_IO,
    },    
    [MT_DEVICE_WC] = {    /* ioremap_wc */
        .prot_pte    = PROT_PTE_DEVICE | L_PTE_MT_DEV_WC,
        .prot_l1    = PMD_TYPE_TABLE,
        .prot_sect    = PROT_SECT_DEVICE,
        .domain        = DOMAIN_IO,
    },
    [MT_UNCACHED] = {
        .prot_pte    = PROT_PTE_DEVICE,
        .prot_l1    = PMD_TYPE_TABLE,
        .prot_sect    = PMD_TYPE_SECT | PMD_SECT_XN,
        .domain        = DOMAIN_IO,
    },
    [MT_CACHECLEAN] = {
        .prot_sect = PMD_TYPE_SECT | PMD_SECT_XN,
        .domain    = DOMAIN_KERNEL,
    },
    [MT_MINICLEAN] = {
        .prot_sect = PMD_TYPE_SECT | PMD_SECT_XN | PMD_SECT_MINICACHE,
        .domain    = DOMAIN_KERNEL,
    },
    [MT_LOW_VECTORS] = {
        .prot_pte  = L_PTE_PRESENT | L_PTE_YOUNG | L_PTE_DIRTY |
                L_PTE_EXEC,
        .prot_l1   = PMD_TYPE_TABLE,
        .domain    = DOMAIN_USER,
    },
    [MT_HIGH_VECTORS] = {
        .prot_pte  = L_PTE_PRESENT | L_PTE_YOUNG | L_PTE_DIRTY |
                L_PTE_USER | L_PTE_EXEC,
        .prot_l1   = PMD_TYPE_TABLE,
        .domain    = DOMAIN_USER,
    },
    [MT_MEMORY] = {
        .prot_sect = PMD_TYPE_SECT | PMD_SECT_AP_WRITE,
        .domain    = DOMAIN_KERNEL,
    },
    [MT_ROM] = {
        .prot_sect = PMD_TYPE_SECT,
        .domain    = DOMAIN_KERNEL,
    },
    [MT_MEMORY_NONCACHED] = {
        .prot_sect = PMD_TYPE_SECT | PMD_SECT_AP_WRITE,
        .domain    = DOMAIN_KERNEL,
    },
};