轉自：http://blog.csdn.net/myarrow/article/details/8609564

1. 簡介

　　內核提供了一個重要的結構體struct machine_desc ，這個結構體在內核移植中起到相當重要的作用，內核通過machine_desc結構體來控制系統體系架構相關部分的初始化。

?????? machine_desc結構體通過MACHINE_START宏來初始化，在代碼中， 通過在start_kernel->setup_arch中調用setup_machine_fdt來獲取。

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2. machine_desc結構體

???????? machine_desc結構體定義如下：

?

[cpp]?view plaincopy

/*?在文件：arch/arm/include/asm/mach/arch.h?*/??

struct?machine_desc?{??

????unsigned?int????????nr;?????/*?architecture?number??*/??

????const?char??????*name;??????/*?architecture?name????*/??

????unsigned?long???????boot_params;????/*?tagged?list??????*/??

????const?char??????**dt_compat;????/*?array?of?device?tree?

?????????????????????????*?'compatible'?strings?*/??

??

????unsigned?int????????nr_irqs;????/*?number?of?IRQs?*/??

??

????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??*/??

????void????????????(*init_early)(void);??

????void????????????(*init_irq)(void);??

????struct?sys_timer????*timer;?????/*?system?tick?timer????*/??

????void????????????(*init_machine)(void);??

#ifdef?CONFIG_MULTI_IRQ_HANDLER??

????void????????????(*handle_irq)(struct?pt_regs?*);??

#endif??

};??

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?3. machine_desc初始化

machine_desc初始化例子如下：

[cpp]?view plaincopy

MACHINE_START(MA,?"myboard")??

????.boot_params????=?PLAT_PHYS_OFFSET?+?0x800,??

????.fixup??????=?ma_fixup,??

????.reserve?????????????=?&ma_reserve,??//內存在交給Linux管理之前，進行預留??

????.map_io?????=?ma_map_io,??

????.init_irq???=?ma_init_irq,??

????.timer??????=?&ma_timer,??

????.init_machine???=?machine_ma_board_init,??

MACHINE_END??

MACHINE_START和MACHINE_END宏定義如下：

[cpp]?view plaincopy

/*?

?*?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?????????????\??

};??

轉載于:https://www.cnblogs.com/sky-heaven/p/4837252.html

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