转自：http://blog.csdn.net/myarrow/article/details/8609564
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 \
- };