（转载）MACHINE_START MACHINE_END 宏
一、定义
[cpp]
#define MACHINE_START(_type,_name) \ //板类型,板名字
static const struct machine_desc __mach_desc_##_type \
__used \
__attribute__((__section__(".arch.info.init"))) = { \
.nr = MACH_TYPE_##_type, \
.name = _name,
#define MACHINE_END \
};
MACHINE_START和MACHINE_END框起了一个machine_desc结构体的声明并根据MACHINE_START宏的参数初始化其.nr和.name成员
并将该结构体标记编译到.arch.info.init段
在MACHINE_START和MACHINE_END宏之间可以初始化machine_desc结构体的剩余成员
machine_desc结构体的定义
[cpp]
struct machine_desc {
unsigned int nr; /* architecture number 编号 */
const char *name; /* architecture name 名字 */
unsigned long boot_params; /* tagged list */
unsigned int nr_irqs; /* number of IRQs 中断数 */
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 io映射函数 */
void (*init_irq)(void); /* 中断初始化函数 */
struct sys_timer *timer; /* system tick timer 滴答定时器 */
void (*init_machine)(void); /* 初始化函数 */
};
使用例子:
[cpp]
MACHINE_START(SMDKC110, "SMDKC110")
/* Maintainer: Kukjin Kim <kgene.kim@samsung.com> */
.boot_params = S5P_PA_SDRAM + 0x100,
.init_irq = s5pv210_init_irq,
.map_io = smdkc110_map_io,
.init_machine = smdkc110_machine_init,
.timer = &s3c24xx_timer,
MACHINE_END
这里smdkc110_machine_init就是对应的板级初始化函数,s5pv210_init_irq就是板级中断初始化函数,smdkc110_map_io就是板级io初始化函数...
二、调用关系
MACHINE_START宏将machine_desc标记编译到.arch.info.init段,而/arch/arm/kernel/vmlinux.lds中
[cpp]
__arch_info_begin = .;
*(.arch.info.init)
__arch_info_end = .;
在linux启动函数start_kernel中调用了setup_arch(&command_line);
[cpp]
void __init setup_arch(char **cmdline_p)
{
struct tag *tags = (struct tag *)&init_tags;
struct machine_desc *mdesc; //声明了一个machine_desc结构体指针
char *from = default_command_line;
init_tags.mem.start = PHYS_OFFSET;
unwind_init();
setup_processor();
mdesc = setup_machine(machine_arch_type); //0根据machine_arch_type获取machine_desc
machine_name = mdesc->name; //设置名字
if (mdesc->soft_reboot) //需要软重启?
reboot_setup("s");
if (__atags_pointer)
tags = phys_to_virt(__atags_pointer);
else if (mdesc->boot_params) { //处理启动参数
#ifdef CONFIG_MMU
if (mdesc->boot_params < PHYS_OFFSET ||
mdesc->boot_params >= PHYS_OFFSET + SZ_1M) {
printk(KERN_WARNING"Default boot params at physical 0x%08lx out of reach\n",mdesc->boot_params);
} else
#endif
{
tags = phys_to_virt(mdesc->boot_params);
}
}
#if defined(CONFIG_DEPRECATED_PARAM_STRUCT)
if (tags->hdr.tag != ATAG_CORE)
convert_to_tag_list(tags);
#endif
if (tags->hdr.tag != ATAG_CORE)
tags = (struct tag *)&init_tags;
if (mdesc->fixup) //若存在fixup方法则调用其方法
mdesc->fixup(mdesc, tags, &from, &meminfo);
if (tags->hdr.tag == ATAG_CORE) {
if (meminfo.nr_banks != 0)
squash_mem_tags(tags);
save_atags(tags);
parse_tags(tags);
}
init_mm.start_code = (unsigned long) _text;
init_mm.end_code = (unsigned long) _etext;
init_mm.end_data = (unsigned long) _edata;
init_mm.brk = (unsigned long) _end;
/* parse_early_param needs a boot_command_line */
strlcpy(boot_command_line, from, COMMAND_LINE_SIZE);
/* populate cmd_line too for later use, preserving boot_command_line */
strlcpy(cmd_line, boot_command_line, COMMAND_LINE_SIZE);
*cmdline_p = cmd_line;
parse_early_param();
arm_memblock_init(&meminfo, mdesc); //这里可能会调用reserve方法
paging_init(mdesc); //->devicemaps_init(mdesc)->map_io方法
request_standard_resources(&meminfo, mdesc); //这里可能会调用video_start方法
#ifdef CONFIG_SMP
if (is_smp())
smp_init_cpus();
#endif
reserve_crashkernel();
cpu_init();
tcm_init();
arch_nr_irqs = mdesc->nr_irqs; //1设置全局变量 中断个数
init_arch_irq = mdesc->init_irq; //2设置全局变量 中断初始化函数
system_timer = mdesc->timer; //3设置全局变量 sys_timer结构体
init_machine = mdesc->init_machine; //4设置全局变量 板级初始化函数
#ifdef CONFIG_VT
#if defined(CONFIG_VGA_CONSOLE)
conswitchp = &vga_con;
#elif defined(CONFIG_DUMMY_CONSOLE)
conswitchp = &dummy_con;
#endif
#endif
early_trap_init();
}
0.
[cpp]
static struct machine_desc * __init setup_machine(unsigned int nr)
{
extern struct machine_desc __arch_info_begin[], __arch_info_end[];
struct machine_desc *p;
for (p = __arch_info_begin; p < __arch_info_end; p++)//遍历__arch_info_begin和__arch_info_end之间的machine_desc结构体
if (nr == p->nr) { //找到对应的板
printk("Machine: %s\n", p->name);//打印板级信息
return p;
}
early_print("\n"
"Error: unrecognized/unsupported machine ID (r1 = 0x%08x).\n\n"
"Available machine support:\n\nID (hex)\tNAME\n", nr);
for (p = __arch_info_begin; p < __arch_info_end; p++)
early_print("%08x\t%s\n", p->nr, p->name);
early_print("\nPlease check your kernel config and/or bootloader.\n");
while (true)
/* can't use cpu_relax() here as it may require MMU setup */;
}
1.中断个数
start_kernel->early_irq_init->arch_probe_nr_irqs函数中nr_irqs = arch_nr_irqs ? arch_nr_irqs : NR_IRQS;设置全局nr_irqs变量
2.中断初始化函数
start_kernel->init_IRQ->init_arch_irq()
3.sys_timer结构体
start_kernel->time_init()调用system_timer->init()方法既sys_timer->init()
4.板级初始化函数
[cpp]
static void (*init_machine)(void) __initdata;
static int __init customize_machine(void)
{
/* customizes platform devices, or adds new ones */
if (init_machine)//全局函数init_machine存在
init_machine();//则调用,既mdesc->init_machine()
return 0;
}
arch_initcall(customize_machine);//用arch_initcall修饰customize_machine函数
arch_iniitcall函数在/include/linux/init.h中定义
[cpp]
#define arch_initcall(fn) __define_initcall("3",fn,3)
__define_initcall的定义
[cpp]
#define __define_initcall(level,fn,id) \
static initcall_t __initcall_##fn##id __used \
__attribute__((__section__(".initcall" level ".init"))) = fn
展开就是static initcall_t __initcall_customize_machine3 __used __attribute__((__section__(".initcall3.init")))=customize_machine
在vmlinux.lds中
[cpp]
__initcall_start = .;
*(.initcallearly.init)
__early_initcall_end = .;
*(.initcall0.init)
*(.initcall0s.init)
*(.initcall1.init)
*(.initcall1s.init)
*(.initcall2.init)
*(.initcall2s.init)
*(.initcall3.init)
*(.initcall3s.init)
*(.initcall4.init)
*(.initcall4s.init)
*(.initcall5.init)
*(.initcall5s.init)
*(.initcallrootfs.init)
*(.initcall6.init)
*(.initcall6s.init)
*(.initcall7.init)
*(.initcall7s.init)
__initcall_end = .;
标注为.initcall3.init的函数编译进__initcall_start和__initcall_end框起的section中
而在系统启动的时候
start_kernel->rest_init()->kernel_thread(kernel_init, NULL, CLONE_FS | CLONE_SIGHAND);创建了kernel线程
kernel_init->do_pre_smp
static void __init do_pre_smp_initcalls(void)
{
initcall_t *fn;
for (fn = __initcall_start; fn < __early_initcall_end; fn++)
do_one_initcall(*fn);
}
该函数遍历__initcall_start和__early_initcall_end中的函数,并调用do_one_initcall
[cpp]
int __init_or_module do_one_initcall(initcall_t fn)
{
int count = preempt_count();
int ret;
if (initcall_debug)
ret = do_one_initcall_debug(fn);
else
ret = fn();//执行了fn函数也就是customize_machine
msgbuf[0] = 0;
if (ret && ret != -ENODEV && initcall_debug)
sprintf(msgbuf, "error code %d ", ret);
if (preempt_count() != count) {
strlcat(msgbuf, "preemption imbalance ", sizeof(msgbuf));
preempt_count() = count;
}
if (irqs_disabled()) {
strlcat(msgbuf, "disabled interrupts ", sizeof(msgbuf));
local_irq_enable();
}
if (msgbuf[0]) {
printk("initcall %pF returned with %s\n", fn, msgbuf);
}
return ret;
}
