machine_desc结构体

原文地址：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
};

/* 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(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 \
};