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1. 简介

　　内核提供了一个重要的结构体struct machine_desc ，这个结构体在内核移植中起到相当重要的作用，内核通过machine_desc结构体来控制系统体系架构相关部分的初始化。

       machine_desc结构体通过MACHINE_START宏来初始化，在代码中， 通过在start_kernel->setup_arch中调用setup_machine_fdt来获取。

 

2. machine_desc结构体

         machine_desc结构体定义如下：

 

/* 在文件：arch/arm/include/asm/mach/arch.h */
struct machine_desc {
    unsigned int        nr;     /* architecture number  */
    const char      *name;      /* architecture name    */
    unsigned long       boot_params;    /* tagged list      */
    const char      **dt_compat;    /* array of device tree
                         * 'compatible' strings */

    unsigned int        nr_irqs;    /* number of IRQs */

    unsigned int        video_start;    /* start of video RAM   */
    unsigned int        video_end;  /* end of video RAM */

    unsigned int        reserve_lp0 :1; /* never has lp0    */
    unsigned int        reserve_lp1 :1; /* never has lp1    */
    unsigned int        reserve_lp2 :1; /* never has lp2    */
    unsigned int        soft_reboot :1; /* soft reboot      */
    void            (*fixup)(struct machine_desc *,
                     struct tag *, char **,
                     struct meminfo *);
    void            (*reserve)(void);/* reserve mem blocks  */
    void            (*map_io)(void);/* IO mapping function  */
    void            (*init_early)(void);
    void            (*init_irq)(void);
    struct sys_timer    *timer;     /* system tick timer    */
    void            (*init_machine)(void);
#ifdef CONFIG_MULTI_IRQ_HANDLER
    void            (*handle_irq)(struct pt_regs *);
#endif
};

 

 3. machine_desc初始化

machine_desc初始化例子如下：

MACHINE_START(MA, "myboard")
    .boot_params    = PLAT_PHYS_OFFSET + 0x800,
    .fixup      = ma_fixup,
    .reserve             = &ma_reserve,  //内存在交给Linux管理之前，进行预留
    .map_io     = ma_map_io,
    .init_irq   = ma_init_irq,
    .timer      = &ma_timer,
    .init_machine   = machine_ma_board_init,
MACHINE_END

MACHINE_START和MACHINE_END宏定义如下：

/*
 * Set of macros to define architecture features.  This is built into
 * a table by the linker.
 */
#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             \
};