init_machine 在Kernel中被调用的过程

以tiny4412为例：

arch/arm/mach-exynos/mach-tiny4412.c

MACHINE_START(TINY4412, "TINY4412")
    /* Maintainer: FriendlyARM (www.arm9.net) */
    .boot_params    = S5P_PA_SDRAM + 0x100,
    .init_irq    = exynos4_init_irq,
    .map_io        = smdk4x12_map_io,
    .init_machine    = smdk4x12_machine_init,
    .timer        = &exynos4_timer,
    .reserve    = &exynos4_reserve,
MACHINE_END

其中：

#define MACHINE_START(_type,_name)            static const struct machine_desc __mach_desc_##_type     __used                             __attribute__((__section__(".arch.info.init"))) = {        .nr        = MACH_TYPE_##_type,            .name        = _name,

#define MACHINE_END                \
};

启动时：

start_kernel  ----- init/main.c

---->  setup_arch ---- arch/arm/kernel/setup.c

---->  mdesc = setup_machine_tags(machine_arch_type);   到这里，根据machine_arch_type就找到上面这个结构体了。

---->  machine_desc = mdesc;

                      ---->  paging_init(mdesc)   (arch/arm/mm/mmu.c)

----> devicemaps_init(mdesc)

----> mdesc->map_io()   调用了函数 smdk4x12_map_io