machine_desc结构体

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				\
};