uboot移植之标记列表

Bootloader 将参数放在某个约定的地方之后，再启动内核，内核启动后从这个地方获得参数。
除了约定好参数存放的地址外，还要规定参数的结构。Linux 2.4.x 以后的内核都期望 以
标记列表（tagged list）的形式来传递启动参数。标记，就是一种数据结构；标记列表，就是
挨着存放的多个标记。
标记列表以标记ATAG_CORE 开始，以标记ATAG_NONE 结束。
标记的数据结构为tag，它由一个tag_header 结构和一个联合（union）组成。
tag_header结构表示标记的类型及长度，比如是表示内存还是表示命令行参数等。
对于不同类型的标记使用不同的联合（union），比如表示内存时使用tag_mem32，表示命令行时使用tag_cmdline。
数据结构tag 和tag_header 定义在Linux 内核源码的uboot/include/asm-arm/setup.h头文件中
参考嵌入式Linux应用开发完全手册ch15.1 p243

uboot/include/asm-arm/setup.h标记列表类型定义

/*
 *  linux/include/asm/setup.h
 *
 *  Copyright (C) 1997-1999 Russell King
 *
 * 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.
 *
 *  Structure passed to kernel to tell it about the
 *  hardware it's running on.  See linux/Documentation/arm/Setup
 *  for more info.
 *
 * NOTE:
 *  This file contains two ways to pass information from the boot
 *  loader to the kernel. The old struct param_struct is deprecated,
 *  but it will be kept in the kernel for 5 years from now
 *  (2001). This will allow boot loaders to convert to the new struct
 *  tag way.
 */
#ifndef __ASMARM_SETUP_H
#define __ASMARM_SETUP_H

/*
 * Usage:
 *  - do not go blindly adding fields, add them at the end
 *  - when adding fields, don't rely on the address until
 *    a patch from me has been released
 *  - unused fields should be zero (for future expansion)
 *  - this structure is relatively short-lived - only
 *    guaranteed to contain useful data in setup_arch()
 */
#define COMMAND_LINE_SIZE 1024

/* This is the old deprecated way to pass parameters to the kernel */
struct param_struct {
    union {
	struct {
	    unsigned long page_size;		/*  0 */
	    unsigned long nr_pages;		/*  4 */
	    unsigned long ramdisk_size;		/*  8 */
	    unsigned long flags;		/* 12 */
#define FLAG_READONLY	1
#define FLAG_RDLOAD	4
#define FLAG_RDPROMPT	8
	    unsigned long rootdev;		/* 16 */
	    unsigned long video_num_cols;	/* 20 */
	    unsigned long video_num_rows;	/* 24 */
	    unsigned long video_x;		/* 28 */
	    unsigned long video_y;		/* 32 */
	    unsigned long memc_control_reg;	/* 36 */
	    unsigned char sounddefault;		/* 40 */
	    unsigned char adfsdrives;		/* 41 */
	    unsigned char bytes_per_char_h;	/* 42 */
	    unsigned char bytes_per_char_v;	/* 43 */
	    unsigned long pages_in_bank[4];	/* 44 */
	    unsigned long pages_in_vram;	/* 60 */
	    unsigned long initrd_start;		/* 64 */
	    unsigned long initrd_size;		/* 68 */
	    unsigned long rd_start;		/* 72 */
	    unsigned long system_rev;		/* 76 */
	    unsigned long system_serial_low;	/* 80 */
	    unsigned long system_serial_high;	/* 84 */
	    unsigned long mem_fclk_21285;       /* 88 */
	} s;
	char unused[256];
    } u1;
    union {
	char paths[8][128];
	struct {
	    unsigned long magic;
	    char n[1024 - sizeof(unsigned long)];
	} s;
    } u2;
    char commandline[COMMAND_LINE_SIZE];
};


/*
 * The new way of passing information: a list of tagged entries
 */

/* The list ends with an ATAG_NONE node. */
#define ATAG_NONE	0x00000000

struct tag_header {
	u32 size;
	u32 tag;
};

/* The list must start with an ATAG_CORE node */
#define ATAG_CORE	0x54410001

struct tag_core {
	u32 flags;		/* bit 0 = read-only */
	u32 pagesize;
	u32 rootdev;
};

/* it is allowed to have multiple ATAG_MEM nodes */
#define ATAG_MEM	0x54410002

struct tag_mem32 {
	u32	size;
	u32	start;	/* physical start address */
};

/* VGA text type displays */
#define ATAG_VIDEOTEXT	0x54410003

struct tag_videotext {
	u8		x;
	u8		y;
	u16		video_page;
	u8		video_mode;
	u8		video_cols;
	u16		video_ega_bx;
	u8		video_lines;
	u8		video_isvga;
	u16		video_points;
};

/* describes how the ramdisk will be used in kernel */
#define ATAG_RAMDISK	0x54410004

struct tag_ramdisk {
	u32 flags;	/* bit 0 = load, bit 1 = prompt */
	u32 size;	/* decompressed ramdisk size in _kilo_ bytes */
	u32 start;	/* starting block of floppy-based RAM disk image */
};

/* describes where the compressed ramdisk image lives (virtual address) */
/*
 * this one accidentally used virtual addresses - as such,
 * its depreciated.
 */
#define ATAG_INITRD	0x54410005

/* describes where the compressed ramdisk image lives (physical address) */
#define ATAG_INITRD2	0x54420005

struct tag_initrd {
	u32 start;	/* physical start address */
	u32 size;	/* size of compressed ramdisk image in bytes */
};

/* board serial number. "64 bits should be enough for everybody" */
#define ATAG_SERIAL	0x54410006

struct tag_serialnr {
	u32 low;
	u32 high;
};

/* board revision */
#define ATAG_REVISION	0x54410007

struct tag_revision {
	u32 rev;
};

/* initial values for vesafb-type framebuffers. see struct screen_info
 * in include/linux/tty.h
 */
#define ATAG_VIDEOLFB	0x54410008

struct tag_videolfb {
	u16		lfb_width;
	u16		lfb_height;
	u16		lfb_depth;
	u16		lfb_linelength;
	u32		lfb_base;
	u32		lfb_size;
	u8		red_size;
	u8		red_pos;
	u8		green_size;
	u8		green_pos;
	u8		blue_size;
	u8		blue_pos;
	u8		rsvd_size;
	u8		rsvd_pos;
};

/* command line: \0 terminated string */
#define ATAG_CMDLINE	0x54410009

struct tag_cmdline {
	char	cmdline[1];	/* this is the minimum size */
};

/* acorn RiscPC specific information */
#define ATAG_ACORN	0x41000101

struct tag_acorn {
	u32 memc_control_reg;
	u32 vram_pages;
	u8 sounddefault;
	u8 adfsdrives;
};

/* footbridge memory clock, see arch/arm/mach-footbridge/arch.c */
#define ATAG_MEMCLK	0x41000402

struct tag_memclk {
	u32 fmemclk;
};

struct tag {
	struct tag_header hdr;
	union {
		struct tag_core		core;//标记起始
		struct tag_mem32	mem;//内存标记，告诉内核内存的分布
		struct tag_videotext	videotext;//
		struct tag_ramdisk	ramdisk;
		struct tag_initrd	initrd;
		struct tag_serialnr	serialnr;
		struct tag_revision	revision;
		struct tag_videolfb	videolfb;
		struct tag_cmdline	cmdline;//命令标记，一个字符串，告诉内核要做什么，即在uboot命令中设置的环境变量bootargs
                                                //"console=ttySAC0 noinitrd root=/dev/mtdblock3 init=/linuxrc"

		/*
		 * Acorn specific
		 */
		struct tag_acorn	acorn;

		/*
		 * DC21285 specific
		 */
		struct tag_memclk	memclk;
	} u;
};

struct tagtable {
	u32 tag;
	int (*parse)(const struct tag *);
};

#define __tag __attribute__((unused, __section__(".taglist")))
#define __tagtable(tag, fn) \
static struct tagtable __tagtable_##fn __tag = { tag, fn }

#define tag_member_present(tag,member)				\
	((unsigned long)(&((struct tag *)0L)->member + 1)	\
		<= (tag)->hdr.size * 4)

#define tag_next(t)	((struct tag *)((u32 *)(t) + (t)->hdr.size))
#define tag_size(type)	((sizeof(struct tag_header) + sizeof(struct type)) >> 2)

#define for_each_tag(t,base)		\
	for (t = base; t->hdr.size; t = tag_next(t))

/*
 * Memory map description
 */
#define NR_BANKS 8

struct meminfo {
	int nr_banks;
	unsigned long end;
	struct {
		unsigned long start;
		unsigned long size;
		int           node;
	} bank[NR_BANKS];
};

extern struct meminfo meminfo;

#endif

uboot/lib_arm/bootm.c 标记列表

/*
 * (C) Copyright 2002
 * Sysgo Real-Time Solutions, GmbH <www.elinos.com>
 * Marius Groeger <[email protected]>
 *
 * Copyright (C) 2001  Erik Mouw ([email protected])
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	 See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307	 USA
 *
 */

#include <common.h>
#include <command.h>
#include <image.h>
#include <u-boot/zlib.h>
#include <asm/byteorder.h>

DECLARE_GLOBAL_DATA_PTR;/**获取全局结构体指针gd***gd_t gd，此宏在uboot/include/asm-arm/global_data.h定义,参考blog.csdn.net/songqqnew/article/details/6847699**/

#if defined (CONFIG_SETUP_MEMORY_TAGS) || \
    defined (CONFIG_CMDLINE_TAG) || \
    defined (CONFIG_INITRD_TAG) || \
    defined (CONFIG_SERIAL_TAG) || \
    defined (CONFIG_REVISION_TAG) || \
    defined (CONFIG_VFD) || \
    defined (CONFIG_LCD)
static void setup_start_tag (bd_t *bd);

# ifdef CONFIG_SETUP_MEMORY_TAGS
static void setup_memory_tags (bd_t *bd);
# endif
static void setup_commandline_tag (bd_t *bd, char *commandline);

# ifdef CONFIG_INITRD_TAG
static void setup_initrd_tag (bd_t *bd, ulong initrd_start,
			      ulong initrd_end);
# endif
static void setup_end_tag (bd_t *bd);

# if defined (CONFIG_VFD) || defined (CONFIG_LCD)
static void setup_videolfb_tag (gd_t *gd);
# endif

static struct tag *params;/***************定义tag***************************************/
#endif /* CONFIG_SETUP_MEMORY_TAGS || CONFIG_CMDLINE_TAG || CONFIG_INITRD_TAG */

int do_bootm_linux(int flag, int argc, char *argv[], bootm_headers_t *images)
{
	bd_t	*bd = gd->bd;/***********************获取bd*************************************/
	char	*s;
	int	machid = bd->bi_arch_number;
	void	(*theKernel)(int zero, int arch, uint params);

#ifdef CONFIG_CMDLINE_TAG
	char *commandline = getenv ("bootargs");
#endif

	if ((flag != 0) && (flag != BOOTM_STATE_OS_GO))
		return 1;

	theKernel = (void (*)(int, int, uint))images->ep;

	s = getenv ("machid");
	if (s) {
		machid = simple_strtoul (s, NULL, 16);
		printf ("Using machid 0x%x from environment\n", machid);
	}

	show_boot_progress (15);

	debug ("## Transferring control to Linux (at address %08lx) ...\n",
	       (ulong) theKernel);

#if defined (CONFIG_SETUP_MEMORY_TAGS) || \
    defined (CONFIG_CMDLINE_TAG) || \
    defined (CONFIG_INITRD_TAG) || \
    defined (CONFIG_SERIAL_TAG) || \
    defined (CONFIG_REVISION_TAG) || \
    defined (CONFIG_LCD) || \
    defined (CONFIG_VFD)
	setup_start_tag (bd);
#ifdef CONFIG_SERIAL_TAG
	setup_serial_tag (¶ms);
#endif
#ifdef CONFIG_REVISION_TAG
	setup_revision_tag (¶ms);
#endif
#ifdef CONFIG_SETUP_MEMORY_TAGS
	setup_memory_tags (bd);
#endif
#ifdef CONFIG_CMDLINE_TAG
	setup_commandline_tag (bd, commandline);
#endif
#ifdef CONFIG_INITRD_TAG
	if (images->rd_start && images->rd_end)
		setup_initrd_tag (bd, images->rd_start, images->rd_end);
#endif
#if defined (CONFIG_VFD) || defined (CONFIG_LCD)
	setup_videolfb_tag ((gd_t *) gd);
#endif
	setup_end_tag (bd);
#endif

	/* we assume that the kernel is in place */
	printf ("\nStarting kernel ...\n\n");

//#ifdef CONFIG_USB_DEVICE
#if 0
	{
		extern void udc_disconnect (void);
		udc_disconnect ();
	}
#endif

	cleanup_before_linux ();

	theKernel (0, machid, bd->bi_boot_params);
	/* does not return */

	return 1;
}


#if defined (CONFIG_SETUP_MEMORY_TAGS) || \
    defined (CONFIG_CMDLINE_TAG) || \
    defined (CONFIG_INITRD_TAG) || \
    defined (CONFIG_SERIAL_TAG) || \
    defined (CONFIG_REVISION_TAG) || \
    defined (CONFIG_LCD) || \
    defined (CONFIG_VFD)
static void setup_start_tag (bd_t *bd)
{
	params = (struct tag *) bd->bi_boot_params;/*bi_boot_param=30000100,在uboot/board/mini2440/mini2440.c中指定***param指向参数区首地址，存放参数**/

	params->hdr.tag = ATAG_CORE;//开始标记
	params->hdr.size = tag_size (tag_core);

	params->u.core.flags = 0;
	params->u.core.pagesize = 0;
	params->u.core.rootdev = 0;

	params = tag_next (params);
}


#ifdef CONFIG_SETUP_MEMORY_TAGS
static void setup_memory_tags (bd_t *bd)
{
	int i;

	for (i = 0; i < CONFIG_NR_DRAM_BANKS; i++) {
		params->hdr.tag = ATAG_MEM;//标记类型:内存标记，hdr是struct tag_header类型结构体，为tag一成员
		params->hdr.size = tag_size (tag_mem32);//标记大小

		params->u.mem.start = bd->bi_dram[i].start;//内存起始地址，u是union类型，为tag一成员
		params->u.mem.size = bd->bi_dram[i].size;//内存结束地址

		params = tag_next (params);
	}
}
#endif /* CONFIG_SETUP_MEMORY_TAGS */


static void setup_commandline_tag (bd_t *bd, char *commandline)
{
	char *p;

	if (!commandline)
		return;

	/* eat leading white space */
	for (p = commandline; *p == ' '; p++);

	/* skip non-existent command lines so the kernel will still
	 * use its default command line.
	 */
	if (*p == '\0')
		return;

	params->hdr.tag = ATAG_CMDLINE;//标记类型:命令字符串
	params->hdr.size =
		(sizeof (struct tag_header) + strlen (p) + 1 + 4) >> 2;

	strcpy (params->u.cmdline.cmdline, p);

	params = tag_next (params);
}


#ifdef CONFIG_INITRD_TAG
static void setup_initrd_tag (bd_t *bd, ulong initrd_start, ulong initrd_end)
{
	/* an ATAG_INITRD node tells the kernel where the compressed
	 * ramdisk can be found. ATAG_RDIMG is a better name, actually.
	 */
	params->hdr.tag = ATAG_INITRD2;
	params->hdr.size = tag_size (tag_initrd);

	params->u.initrd.start = initrd_start;
	params->u.initrd.size = initrd_end - initrd_start;

	params = tag_next (params);
}
#endif /* CONFIG_INITRD_TAG */


#if defined (CONFIG_VFD) || defined (CONFIG_LCD)
extern ulong calc_fbsize (void);
static void setup_videolfb_tag (gd_t *gd)
{
	/* An ATAG_VIDEOLFB node tells the kernel where and how large
	 * the framebuffer for video was allocated (among other things).
	 * Note that a _physical_ address is passed !
	 *
	 * We only use it to pass the address and size, the other entries
	 * in the tag_videolfb are not of interest.
	 */
	params->hdr.tag = ATAG_VIDEOLFB;
	params->hdr.size = tag_size (tag_videolfb);

	params->u.videolfb.lfb_base = (u32) gd->fb_base;
	/* Fb size is calculated according to parameters for our panel
	 */
	params->u.videolfb.lfb_size = calc_fbsize();

	params = tag_next (params);
}
#endif /* CONFIG_VFD || CONFIG_LCD */

#ifdef CONFIG_SERIAL_TAG
void setup_serial_tag (struct tag **tmp)
{
	struct tag *params = *tmp;
	struct tag_serialnr serialnr;
	void get_board_serial(struct tag_serialnr *serialnr);

	get_board_serial(&serialnr);
	params->hdr.tag = ATAG_SERIAL;
	params->hdr.size = tag_size (tag_serialnr);
	params->u.serialnr.low = serialnr.low;
	params->u.serialnr.high= serialnr.high;
	params = tag_next (params);
	*tmp = params;
}
#endif

#ifdef CONFIG_REVISION_TAG
void setup_revision_tag(struct tag **in_params)
{
	u32 rev = 0;
	u32 get_board_rev(void);

	rev = get_board_rev();
	params->hdr.tag = ATAG_REVISION;
	params->hdr.size = tag_size (tag_revision);
	params->u.revision.rev = rev;
	params = tag_next (params);
}
#endif  /* CONFIG_REVISION_TAG */


static void setup_end_tag (bd_t *bd)
{
	params->hdr.tag = ATAG_NONE;
	params->hdr.size = 0;
}

#endif /* CONFIG_SETUP_MEMORY_TAGS || CONFIG_CMDLINE_TAG || CONFIG_INITRD_TAG */

2012-12-22 22:19:53 添加
内核在启动的时候会从内存中取得标记列表,使用setup_arch

asmlinkage void __init start_kernel(void)
{
	char * command_line;
	extern const struct kernel_param __start___param[], __stop___param[];

	smp_setup_processor_id();

	/*
	 * Need to run as early as possible, to initialize the
	 * lockdep hash:
	 */
	lockdep_init();
	debug_objects_early_init();

	/*
	 * Set up the the initial canary ASAP:
	 */
	boot_init_stack_canary();

	cgroup_init_early();

	local_irq_disable();
	early_boot_irqs_disabled = true;

/*
 * Interrupts are still disabled. Do necessary setups, then
 * enable them
 */
	tick_init();
	boot_cpu_init();
	page_address_init();
	printk(KERN_NOTICE "%s", linux_banner);
	setup_arch(&command_line);
...
}

setup_arch---------->squash_mem_tags(tags);

static void __init squash_mem_tags(struct tag *tag)
{
	for (; tag->hdr.size; tag = tag_next(tag))
		if (tag->hdr.tag == ATAG_MEM)
			tag->hdr.tag = ATAG_NONE;
}

command_line就是这个时候建立的。内核中也有一个default_command_line，是在内核 Boot options  --->  中定义的。如果在uboot没有传递command_line tag,内核就使用default_command_line。从squash_mem_tags函数可以看出来(uboot没传递的话，在tag list里面就找不到tag_cmdline)