LINUX中的MACH定义之MACHINE_START / MACHINE_END

本文讲解LINUX中用MACHINE_START/MACHINE_END定义的MACH，并给出定义的各个成员函数在初始化过程中被调用的时机。

1. 定义一个MACH

LINUX中MACHINE定义是用MACHINE_START()/MACHINE_END两个宏来实现的，比如MSM的实现（arch/arm/mach-msm/board-halibut.c）：

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MACHINE_START(HALIBUT,"Halibut Board (QCT SURF7200A)") .boot_params = 0x10000100, .map_io = halibut_map_io, .init_irq = halibut_init_irq, .init_machine = halibut_init, .timer = &msm_timer, MACHINE_END

MACHINE_START(HALIBUT,"Halibut Board (QCT SURF7200A)")
.boot_params      = 0x10000100,
.map_io           = halibut_map_io,
.init_irq         = halibut_init_irq,
.init_machine     = halibut_init,
.timer            = &msm_timer,
MACHINE_END

2. MACHINE_START / MACHINE_END定义

上面的定义中，用到了这两个宏MACHINE_START/MACHINE_END，下面是它们具体的定义（在arch/arm/include/asm/mach/arch.h中）：

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#defineMACHINE_START(_type,_name) \
static const structmachine_desc __mach_desc_##_type \
__used \
__attribute__((__section__(".arch.info.init")))= { \
.nr = MACH_TYPE_##_type, \
.name = _name,

#define MACHINE_END \
};

#defineMACHINE_START(_type,_name)                        \
static const structmachine_desc __mach_desc_##_type      \
__used                                                  \
__attribute__((__section__(".arch.info.init")))= {      \
.nr             = MACH_TYPE_##_type,            \
.name           = _name,

#define MACHINE_END                                      \
};

struct machine_desc也是定义在arch/arm/include/asm/mach/arch.h

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struct machine_desc {
/*
* Note! The firstfour elements are used
* by assembler codein 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);
};

struct machine_desc {
/*
* Note! The firstfour elements are used
* by assembler codein 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);
};

3. MACH HALIBUT的定义

把1中定义的MACH展开之后，得到：

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struct machine_desc __mach_desc_HALIBUT{
__used
__attribute__((__section__(".arch.info.init")))= {
.nr = MACH_TYPE_HALIBUT,
.name = "HalibutBoard (QCT SURF7200A)",
.boot_params = 0x10000100,
.map_io = halibut_map_io,
.init_irq = halibut_init_irq,
.init_machine = halibut_init,
.timer = &msm_timer,
};

struct machine_desc __mach_desc_HALIBUT{
__used
__attribute__((__section__(".arch.info.init")))= {
.nr               = MACH_TYPE_HALIBUT,
.name             = "HalibutBoard (QCT SURF7200A)",
.boot_params      = 0x10000100,
.map_io           = halibut_map_io,
.init_irq         = halibut_init_irq,
.init_machine     = halibut_init,
.timer            = &msm_timer,
};

总结一下：MACHINE_START主要是定义了"struct machine_desc"的类型，放在 section(".arch.info.init")，是初始化数据，Kernel 起来之后将被丢弃。

4. 成员函数被调用的时机

在setup_arch() [setup.c#758~760]中init_irq, timer & init_machine分别被赋值给下列变量：

init_arch_irq = mdesc->init_irq;

system_timer = mdesc->timer;

init_machine = mdesc->init_machine;

而这三个函数指针是在下列场景中被调用的：

1) start_kernel()[main.c#589]-> init_IRQ() [irq.c] ->init_arch_irq();

2) start_kernel()[main.c#595]->time_init () [time.c] ->system_time->init();

3) customize_machine()[setup.c#692] -> init_machine();

customize_machine是被放在arch_initcall段的，按照顺序被调用。xxx_initcall段内的函数是按下列顺序被调用的：start_kernel() [main.c#682] -> rest_init()
[启动内核线程]-> kernel_init() –> do_basic_setup()-> do_initcalls();

map_io是在下列顺序中被调用

4) start_kernel()[main.c#546]-> setup_arch () [setup.c#745] -> paging_init() [mmu.c#1028] -> devicemaps_init()[mmu.c#993] -> map_io()

从它们在start_kernel()中被调用的顺序，可知它们执行的先后为：map_io; init_irq; timer->time_init; init_machine。