Machine_start/machine_end defined by Mach in Linux

Machine_start/machine_end defined by Mach in Linux

 

Tian haili @ csdn

2011/08/18

 

This article describes the Mach defined by machine_start/machine_end in Linux, and provides the time for each defined member function to be called during initialization.

 

1. Define a Mach

In Linux, machine is defined by using two macros, machine_start ()/machine_end, such as implementation of MSM (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 Definition

The two macros machine_start/machine_end are used in the above definition. The specific definitions are as follows (in arch/ARM/include/ASM/Mach/arch. h ):

#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_descIt is also defined in 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. Definition of Mach halibut

Expand the Mach defined in 1 and get the following result:

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,};

To sum up, machine_start mainly defines the type of "struct machine_desc", which is placed in section (".arch.info. init"). It is the initialization data and will be discarded after the kernel is up.

 

4. When a member function is called

In setup_arch () [setup. C #758 ~ In 760], init_irq, Timer & init_machine are assigned to the following variables:

Init_arch_irq = mdesc->Init_irq;

System_timer = mdesc->Timer;

Init_machine = mdesc->Init_machine;

These three function pointers are called in the following scenarios:

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 is put in the arch_initcall segment and called in order. Functions in the xxx_initcall segment are called in the following order: start_kernel ()[Main. C #682.]-> Rest_init () [start the kernel thread]-> kernel_init ()-> do_basic_setup ()-> do_initcils ();

Map_ioIs called in the following order

4) start_kernel ()[Main. C #546.]-> Setup_arch () [setup. C #745]-> paging_init () [MMU. C #1028]-> devicemaps_init () [MMU. C #993]-> map_io ()

 

From the sequence in start_kernel (), we can see that they are executed successively as map_io; init_irq; timer-> time_init; init_machine.

 

*** Welcome to reprint, and please indicate the original from http://blog.csdn.net/thl789/article/details/6699259 ***