MACHINE_START and MACHINE_END Macro define

***************************************************************************************************************************
作者：EasyWave                                                                                 时间：2012.02.11

类别：linux驱动开发                                                                           声明：转载，请保留链接

***************************************************************************************************************************

在linux-2.6.38中，/arch/arm/mach-w90x900/mach-nuc950evb.c文件的最后部分，有如下宏定义:

MACHINE_START(W90P950EVB, "W90P950EVB")
 .phys_io = W90X900_PA_UART,
 .io_pg_offst = (((u32)W90X900_VA_UART) >> 18) & 0xfffc, 
 .boot_params =  0x100,
 .map_io  = nuc950evb_map_io,
 .init_irq = nuc900_init_irq,
 .init_machine = nuc950evb_init,
 .timer  = &nuc900_timer,
MACHINE_END

 

而MACHINE_START和MACHINE_END宏定义在arch/arm/include/asm/mach/arch.h，如下：

struct machine_desc {
 /*
  * Note! The first four elements are used
  * by assembler code in 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);
};

/*
 * 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    \
};

#endif

 

将前面定义的MACHINE_START和MACHINE_END展开后得到:
static  const struct machine_desc __mach_desc_W90P950EVB __used __attribute__((__section__(".arch.info.init"))) = {
.nr = MACH_TYPE_W90P950EVB, /* architecture number */
.name = "W90P950EVB"", /* architecture name */
.phys_io = W90X900_PA_UART, /* start of physical io */
.io_pg_offst = (((u32)W90X900_VA_UART) >> 18) & 0xfffc,
.boot_params = 0x100, /* tagged list */
.map_io = nuc950evb_map_io, /* IO mapping function */
.init_irq = nuc900_init_irq,
.init_machine = nuc950evb_init,
.timer = &nuc900_timer,
}

MACH_TYPE_W90P950EVB定义在arch/arm/include/asm/mach-types.h内，值为1860 十六进制为：0x744.
#define MACH_TYPE_W90P950EVB             1860

这个值是机器的类型值，编译时由arch/arm/tool/mach- types里面定义的数据生成的。
/* arch/arm/tool/mach-types */
w90x900   MACH_W90X900  W90X900   1860

而在arch/arm/kernel/head-common.S文件中的__lookup_machine_type函数中有如下的定义：

/*
 *  linux/arch/arm/kernel/head-common.S
 *
 *  Copyright (C) 1994-2002 Russell King
 *  Copyright (c) 2003 ARM Limited
 *  All Rights Reserved
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 */

#define ATAG_CORE 0x54410001
#define ATAG_CORE_SIZE ((2*4 + 3*4) >> 2)
#define ATAG_CORE_SIZE_EMPTY ((2*4) >> 2)

 .align 2
 .type __switch_data, %object
__switch_data:
...................中间省略

 .long processor_id                   @ r4
 .long __machine_arch_type    @ r5
 .long __atags_pointer              @ r6
 .long cr_alignment                   @ r7
 .long init_thread_union + THREAD_START_SP  @ sp

 ...................中间省略

/*
 * Look in <asm/procinfo.h> and arch/arm/kernel/arch.[ch] for
 * more information about the __proc_info and __arch_info structures.
 */
 .align 2
3: .long __proc_info_begin
 .long __proc_info_end
4: .long .
 .long __arch_info_begin
 .long __arch_info_end

/*
 * Lookup machine architecture in the linker-build list of architectures.
 * Note that we can't use the absolute addresses for the __arch_info
 * lists since we aren't running with the MMU on (and therefore, we are
 * not in the correct address space).  We have to calculate the offset.
 *
 *  r1 = machine architecture number
 * Returns:
 *  r3, r4, r6 corrupted
 *  r5 = mach_info pointer in physical address space
 */
__lookup_machine_type:
#ifdef CONFIG_ARCH_W90X900     //这个就是前面的1860,十六进制为:0x744
       mov      r1, #0x700
       add      r1, r1, #0x40
       add      r1, r1, #0x04
#endif
 adr r3, 4b
 ldmia r3, {r4, r5, r6}
 sub r3, r3, r4   @ get offset between virt&phys
 add r5, r5, r3   @ convert virt addresses to
 add r6, r6, r3   @ physical address space
1: ldr r3, [r5, #MACHINFO_TYPE] @ get machine type
 teq r3, r1    @ matches loader number?
 beq 2f    @ found
 add r5, r5, #SIZEOF_MACHINE_DESC @ next machine_desc
 cmp r5, r6
 blo 1b
 mov r5, #0    @ unknown machine
2: mov pc, lr
ENDPROC(__lookup_machine_type)

函数说明：

adr r3,4b : 取地址指令,这里的4b 是向后symbol名称是4的位置,即4: .long .的位置,将该地址存入r3，r3中存放的是4b处物理地址.
        r5存的是__arch_info_begin 的地址
        r6存的是__arch_info_end 的地址

arm linux 从入口到start_kernel 代码分析

__arch_info_begin 和 __arch_info_end是在 arch/arm/kernel/vmlinux.lds.S中:

          __arch_info_begin = .;
          *(.arch.info.init)
          __arch_info_end = .;    

        这里是声明了两个变量:__arch_info_begin 和 __arch_info_end,其中等号后面的"."是location counter(详细内容请参考ld.info)，这三行的意思是: __arch_info_begin 的位置上,放置所有文件中的 ".arch.info.init" 段的内容,然后紧接着是 __arch_info_end 的位置.

teq r3, r1    @ matches loader number?
如果R1中存储的值和mach-types.h不一致的话，会出现下面的错误：

Machine configuration botched (nr xxxx), unable to continue.不同的版本会出现的警报不一致。

在arch/arm/kernel/setup.c中：

void __init setup_arch(char **cmdline_p)
{
 struct tag *tags = (struct tag *)&init_tags;
 struct machine_desc *mdesc;
 char *from = default_command_line;

 unwind_init();

 setup_processor();
 mdesc = setup_machine(machine_arch_type);
 machine_name = mdesc->name;

 if (mdesc->soft_reboot)
  reboot_setup("s");

 if (__atags_pointer)
  tags = phys_to_virt(__atags_pointer);
 else if (mdesc->boot_params)
  tags = phys_to_virt(mdesc->boot_params);

 /*
  * If we have the old style parameters, convert them to
  * a tag list.
  */
 if (tags->hdr.tag != ATAG_CORE)
  convert_to_tag_list(tags);
 if (tags->hdr.tag != ATAG_CORE)
  tags = (struct tag *)&init_tags;

 if (mdesc->fixup)
  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();

 paging_init(mdesc);
 request_standard_resources(&meminfo, mdesc);

#ifdef CONFIG_SMP
 smp_init_cpus();
#endif

 cpu_init();
 tcm_init();

 /*
  * Set up various architecture-specific pointers
  */
 init_arch_irq = mdesc->init_irq;
 system_timer = mdesc->timer;
 init_machine = mdesc->init_machine;

#ifdef CONFIG_VT
#if defined(CONFIG_VGA_CONSOLE)
 conswitchp = &vga_con;
#elif defined(CONFIG_DUMMY_CONSOLE)
 conswitchp = &dummy_con;
#endif
#endif
 early_trap_init();
}

而setup_machine(unsigned int nr)函数也是在arch/arm/kernel/setup.c中定义：

static struct machine_desc * __init setup_machine(unsigned int nr)
{
 struct machine_desc *list;

 /*
  * locate machine in the list of supported machines.
  */
 list = lookup_machine_type(nr); //看到了吧，这个才是重点
 if (!list) {
  printk("Machine configuration botched (nr %d), unable "
         "to continue.\n", nr);
  while (1);
 }

 printk("Machine: %s\n", list->name);

 return list;
}

因此就会出现：Machine configuration botched (nr xxxx), unable to continue.的警告信息。

 

各个成员函数在不同时期被调用：
1. .init_machine 在 arch/arm/kernel/setup.c 中被 customize_machine 调用，放在 arch_initcall() 段里面，会自动按顺序被调用。
2. init_irq在start_kernel() --> init_IRQ() --> init_arch_irq() 被调用
3. map_io 在 setup_arch() --> paging_init() --> devicemaps_init()被调用
其他主要都在 setup_arch() 中用到。