LINUX中的MACH定義之MACHINE_START / MACHINE_END

LINUX中的MACH定義之MACHINE_START / MACHINE_END

 

田海立@CSDN

2011/08/18

 

本文講解LINUX中用MACHINE_START/MACHINE_END定義的MACH，並給出定義的各個成員函數在初始化過程中被調用的時機。

 

1.      定義一個MACH

LINUX中MACHINE定義是用MACHINE_START()/MACHINE_END兩個宏來實現的，比如MSM的實現（arch/arm/mach-msm/board-halibut.c）：

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定義

上面的定義中，用到了這兩個宏MACHINE_START/MACHINE_END，下面是它們具體的定義（在arch/arm/include/asm/mach/arch.h中）： 

#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也是定義在arch/arm/include/asm/mach/arch.h

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的定義

把1中定義的MACH展開之後，得到：

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,};

總結一下：MACHINE_START主要是定義了"struct machine_desc"的類型，放在 section(".arch.info.init")，是初始化資料，Kernel 起來之後將被丟棄。

 

4.      成員函數被調用的時機

在setup_arch() [setup.c#758~760]中init_irq, timer & init_machine分別被賦值給下列變數：

         init_arch_irq = mdesc->init_irq;

         system_timer = mdesc->timer;

         init_machine = mdesc->init_machine;

而這三個函數指標是在下列情境中被調用的：

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，按照順序被調用。xxx_initcall段內的函數是按下列順序被調用的：start_kernel() [main.c#682] -> rest_init() [啟動核心線程]-> kernel_init() –> do_basic_setup()-> do_initcalls();

map_io是在下列順序中被調用

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

 

從它們在start_kernel()中被調用的順序，可知它們執行的先後為：map_io; init_irq; timer->time_init; init_machine。

 

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