MACHINE_START与MACHINE_END

在移植Linux时，有个结构体需要填写，它以MACHINE_START开始并以MACHINE_END结束，如下mini2440开发板的移植为示例

MACHINE_START(MINI2440, "MINI2440")
	.phys_io	= S3C2410_PA_UART,
	.io_pg_offst	= (((u32)S3C24XX_VA_UART) >> 18) & 0xfffc,
	.boot_params	= S3C2410_SDRAM_PA + 0x100,
	.map_io		= mini2440_map_io,
	.init_machine	= mini2440_init,
	.init_irq	= s3c24xx_init_irq,
	.timer		= &s3c24xx_timer,
MACHINE_END

其中MACHINE_START、MACHINE_END都是定义的宏，代码如下

/*
 * 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				\
};

由上代码可知这两个宏一起定义了一个类型为struct machine_desc的变量，结构体定义如下

struct machine_desc {
	/*
	 * Note! The first four elements are used
	 * by assembler code in head.S, head-common.S
	 */
	unsigned int		nr;		/* architecture number	*/
	unsigned int		phys_io;	/* start of physical io	*/
	unsigned int		io_pg_offst;	/* byte offset for io 
						 * page tabe entry	*/

	const char		*name;		/* architecture name	*/
	unsigned long		boot_params;	/* tagged list		*/

	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			(*map_io)(void);/* IO mapping function	*/
	void			(*init_irq)(void);
	struct sys_timer	*timer;		/* system tick timer	*/
	void			(*init_machine)(void);
};

这个类型的变量放在内核代码段.arch.info.init中，在内核运行初期，被函数lookup_machine_type（此函数用汇编实现，在汇编文件中）取出，读取流程为

Start_kernel() -> setup_arch() -> setup_machine() -> lookup_machine_type()

在函数setup_machine()中，利用这个结构体类型的变量初始化一些全局变量，以备内核运行时使用，比如

init_arch_irq = mdesc->init_irq;

       system_timer = mdesc->timer;

       init_machine = mdesc->init_machine;

 

这个结构体中，成员init_machine保存的是开发板资源注册的初始化代码，init_irq保存的是中断初始化指针，timer保存的是一个struct sys_timer类型的指针…..如果我们要给自己的开发板定制内核，那么我们必须自己实现以上成员函数，其中函数init_machine()是我们向内核传递开发板设备信息的重要的常规途径，分析mini2440开发板内核移植代码知道，在这个函数中，注册了开发板所用到的所有设备的相关硬件信息！

static void __init mini2440_init(void)
{
	struct mini2440_features_t features = { 0 };
	int i;

	printk(KERN_INFO "MINI2440: Option string mini2440=%s\n",
			mini2440_features_str);

	/* Parse the feature string */
	mini2440_parse_features(&features, mini2440_features_str);

	/* turn LCD on */
	s3c_gpio_cfgpin(S3C2410_GPC(0), S3C2410_GPC0_LEND);

	/* Turn the backlight early on */
	WARN_ON(gpio_request(S3C2410_GPG(4), "backlight"));
	gpio_direction_output(S3C2410_GPG(4), 1);

	/* remove pullup on optional PWM backlight -- unused on 3.5 and 7"s */
	s3c_gpio_setpull(S3C2410_GPB(1), S3C_GPIO_PULL_UP);
	s3c2410_gpio_setpin(S3C2410_GPB(1), 0);
	s3c_gpio_cfgpin(S3C2410_GPB(1), S3C2410_GPIO_INPUT);

	/* Make sure the D+ pullup pin is output */
	WARN_ON(gpio_request(S3C2410_GPC(5), "udc pup"));
	gpio_direction_output(S3C2410_GPC(5), 0);

	/* mark the key as input, without pullups (there is one on the board) */
	for (i = 0; i < ARRAY_SIZE(mini2440_buttons); i++) {
		s3c_gpio_setpull(mini2440_buttons[i].gpio, S3C_GPIO_PULL_UP);
		s3c_gpio_cfgpin(mini2440_buttons[i].gpio, S3C2410_GPIO_INPUT);
	}
	if (features.lcd_index != -1) {
		int li;

		mini2440_fb_info.displays =
			&mini2440_lcd_cfg[features.lcd_index];

		printk(KERN_INFO "MINI2440: LCD");
		for (li = 0; li < ARRAY_SIZE(mini2440_lcd_cfg); li++)
			if (li == features.lcd_index)
				printk(" [%d:%dx%d]", li,
					mini2440_lcd_cfg[li].width,
					mini2440_lcd_cfg[li].height);
			else
				printk(" %d:%dx%d", li,
					mini2440_lcd_cfg[li].width,
					mini2440_lcd_cfg[li].height);
		printk("\n");
		s3c24xx_fb_set_platdata(&mini2440_fb_info);
	}

	s3c24xx_udc_set_platdata(&mini2440_udc_cfg);
	s3c24xx_mci_set_platdata(&mini2440_mmc_cfg);
	s3c_nand_set_platdata(&mini2440_nand_info);
	s3c_i2c0_set_platdata(NULL);

	i2c_register_board_info(0, mini2440_i2c_devs,
				ARRAY_SIZE(mini2440_i2c_devs));

	platform_add_devices(mini2440_devices, ARRAY_SIZE(mini2440_devices));

	if (features.count)	/* the optional features */
		platform_add_devices(features.optional, features.count);

}

那么成员函数init_machine什么时候被调用呢？

在函数setup_machine()中有一条语句init_machine = mdesc->init_machine;其中init_machine为全局函数指针变量，此变量在函数customize_machine()中被调用,代码如下所示：

static int __init customize_machine(void)

{

       /* customizes platform devices, or adds new ones */

       if (init_machine)

              init_machine();

       return 0;

}

arch_initcall(customize_machine);

在MACHINE_START与MACHINE_END之间还要填写一些参数，参照结构体注释小心填写即可，最好找个例子参考参考。