linux下lk和kernel层通信方式[2]

U-Boot与Linux内核的交互

说明：本文所使用的U-Boot的版本是1.1.6，平台是S3C2440。

目录

一、简介
1.1标记列表
二、设置标记存放的地址
2.1相关的结构体定义
2.2标记存放地址的设定
三、标记的设置
3.1设置标记ATAG_CORE
3.2设置内存标记ATAG_MEM
3.3设置命令行标记ATAG_CMDLINE
3.4设置ATAG_NONE

一、简介

U-Boot与Linux内核的交互是单向的，U-Boot将各类参数传递给内核。由于他们不能同时运行，传递办法只能有一个个：U-Boot将参数放在某个约定的地方之后，在启动内核，内核启动后从这个地方获得参数。

1.1标记列表

除了约定好参数存放的地方外，还要规定参数的结构。Linux2.4.x以后的内核都以标记列表（tagged list）的形式来传递参数。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ATAGE_NONE结束。

标记的数据结构为tag，它是偶一个tag_header结构和一个联合体（union）组成。tag_header结构体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体，比如表示内存=时使用tag_men32，表示命令行时使用tag_cmdline。其定定义在include/asm-arm/setup.c文件中。

/*
 * 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[]; /* 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;
        struct tag_mem32    mem;
        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;  

        /*
         * Acorn specific
         */
        struct tag_acorn    acorn;  

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

#define tag_next(t)<span style="white-space:pre">   </span>((struct tag *)((u32 *)(t) + (t)->hdr.size))
#define tag_size(type)<span style="white-space:pre">    </span>((sizeof(struct tag_header) + sizeof(struct type)) >> 2) //???  

二、设置标记存放的地址

2.1相关的结构体定义

结构体bd中保存了标记存放的地址。bd结构体是gd结构体的一项，我们先看gd结构体，其定义在include/asm-arm/global_data.h文件中：

typedef struct  global_data {
    bd_t        *bd;//开发板相关参数 ,结构体变量，参考u-boot.h
    unsigned long   flags;//指示标志，如设备已经初始化标志等
    unsigned long   baudrate;//串行口通讯速率
    unsigned long   have_console;
    /* serial_init() was called 如果执行了该函数，则设置为1 */
    unsigned long   reloc_off;
    /*
     *Relocation Offset 重定位偏移，就是实际定向的位置与编译连接时指定的位置之差，一般为0
        */
    unsigned long   env_addr;   /* 环境参数地址*/
    unsigned long   env_valid;  /* 环境参数CRC检验有效标志*/
    unsigned long   fb_base;    /*帧缓冲区基地址*/
#ifdef CONFIG_VFD
    unsigned char   vfd_type;   /* 显示类型*/
#endif
#if 0
    unsigned long   cpu_clk;    /*cpu时钟*/
    unsigned long   bus_clk;    //总线时钟
    unsigned long   ram_size;   /* RAM size */
    unsigned long   reset_status;   /* reset status register at boot */
#endif
    void        **jt;   /* jump table 跳转表，用来登记"函数调用地址"*/
} gd_t;  

接来下我们来看一下bd结构体，这个结构体定义在include/asm-arm/u-boot.h文件中：

typedef struct bd_info {
    int         bi_baudrate;    /* 串口波特率*/
    unsigned long   bi_ip_addr; /*  IP 地址*/
    unsigned char   bi_enetaddr[]; /* MAC地址*/
    struct environment_s           *bi_env;
    ulong           bi_arch_number; /*  板子的id*/
    ulong           bi_boot_params; /* 启动参数*/
    struct              /* RAM 配置*/
    {
    ulong start;
    ulong size;
    }bi_dram[CONFIG_NR_DRAM_BANKS];
#ifdef CONFIG_HAS_ETH1
    /* second onboard ethernet port */
    unsigned char   bi_enet1addr[];
#endif
} bd_t;  

2.2标记存放地址的设定

在board/smdk2410/smdk2410.c的board_init 函数设置了bi_boot_params 参数：

int board_init (void)
{
    S3C24X0_CLOCK_POWER * const clk_power = S3C24X0_GetBase_CLOCK_POWER();//获取时钟和电源配置寄存器的第一个寄存器的地址，寄存器的地上是连续的
    S3C24X0_GPIO * const gpio = S3C24X0_GetBase_GPIO();//获取GPIO配置寄存器的第一个寄存器的地址  

    /* to reduce PLL lock time, adjust the LOCKTIME register */
    clk_power->LOCKTIME = 0xFFFFFF;  

    /* configure MPLL */
    clk_power->MPLLCON = ((M_MDIV << ) + (M_PDIV << ) + M_SDIV);  

    /* some delay between MPLL and UPLL */
    delay ();  

    /* configure UPLL */
    clk_power->UPLLCON = ((U_M_MDIV << ) + (U_M_PDIV << ) + U_M_SDIV);  

    /* some delay between MPLL and UPLL */
    delay ();  

    /* set up the I/O ports */
    gpio->GPACON = 0x007FFFFF;
    gpio->GPBCON = 0x00044555;
    gpio->GPBUP = 0x000007FF;
    gpio->GPCCON = 0xAAAAAAAA;
    gpio->GPCUP = 0x0000FFFF;
    gpio->GPDCON = 0xAAAAAAAA;
    gpio->GPDUP = 0x0000FFFF;
    gpio->GPECON = 0xAAAAAAAA;
    gpio->GPEUP = 0x0000FFFF;
    gpio->GPFCON = 0x000055AA;
    gpio->GPFUP = 0x000000FF;
    gpio->GPGCON = 0xFF95FFBA;
    gpio->GPGUP = 0x0000FFFF;
    gpio->GPHCON = 0x002AFAAA;
    gpio->GPHUP = 0x000007FF;  

    /* arch number of SMDK2410-Board */
    gd->bd->bi_arch_number = MACH_TYPE_SMDK2410;  

    /* adress of boot parameters */
    gd->bd->bi_boot_params = 0x30000100;  

    icache_enable();  //调用cpu/arm920t/cpu.c中的函数
    dcache_enable();  

    return ;
}  

三、标记的设置

U-Boot通过bootm命令引导Linux内核，bootm命令对吼调用do_bootm_linux函数来引导内核。在do_bootm_linux函数就设置了标记，该函数的定义在lib_arm/armlinux.c中：

void do_bootm_linux (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[],
             ulong addr, ulong *len_ptr, int verify)
{
    ulong len = , checksum;
    ulong initrd_start, initrd_end;
    ulong data;
    void (*theKernel)(int zero, int arch, uint params);
    image_header_t *hdr = &header;
    bd_t *bd = gd->bd;  

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

    theKernel = (void (*)(int, int, uint))ntohl(hdr->ih_ep);
    设置kernal加载地址  

    /*
     * Check if there is an initrd image
     */
    用户自定义了initrd之后需要加载进来，整个过程需要进行头部以及整个数据内部校，类似于内核的加载校验，这里省略了。
initial RAM disk　　Linux初始 RAM磁盘（initrd）是在系统引导过程中挂载的一个临时根文件系统，用来支持两阶段的引导过程。initrd文件中包含了各种可执行程序和驱动程序，它们可以用来挂载实际的根文件系统，然后再将这个 initrd RAM 磁盘卸载，并释放内存。在很多嵌入式Linux 系统中，initrd 就是最终的根文件系统。
    if (argc >= ) {
        SHOW_BOOT_PROGRESS ();  

        addr = simple_strtoul (argv[], NULL, );  

        printf ("## Loading Ramdisk Image at %08lx ...\n", addr);  

        /* Copy header so we can blank CRC field for re-calculation */
#ifdef CONFIG_HAS_DATAFLASH
        if (addr_dataflash (addr)) {
            read_dataflash (addr, sizeof (image_header_t),
                    (char *) &header);
        } else
#endif
            memcpy (&header, (char *) addr,
                sizeof (image_header_t));  

        if (ntohl (hdr->ih_magic) != IH_MAGIC) {
            printf ("Bad Magic Number\n");
            SHOW_BOOT_PROGRESS (-);
            do_reset (cmdtp, flag, argc, argv);
        }  

        data = (ulong) & header;
        len = sizeof (image_header_t);  

        checksum = ntohl (hdr->ih_hcrc);
        hdr->ih_hcrc = ;  

        if (crc32 (, (unsigned char *) data, len) != checksum) {
            printf ("Bad Header Checksum\n");
            SHOW_BOOT_PROGRESS (-);
            do_reset (cmdtp, flag, argc, argv);
        }  

        SHOW_BOOT_PROGRESS ();  

        print_image_hdr (hdr);  

        data = addr + sizeof (image_header_t);
        len = ntohl (hdr->ih_size);  

#ifdef CONFIG_HAS_DATAFLASH
        if (addr_dataflash (addr)) {
            read_dataflash (data, len, (char *) CFG_LOAD_ADDR);
            data = CFG_LOAD_ADDR;
        }
#endif  

        if (verify) {
            ulong csum = ;  

            printf ("   Verifying Checksum ... ");
            csum = crc32 (, (unsigned char *) data, len);
            if (csum != ntohl (hdr->ih_dcrc)) {
                printf ("Bad Data CRC\n");
                SHOW_BOOT_PROGRESS (-);
                do_reset (cmdtp, flag, argc, argv);
            }
            printf ("OK\n");
        }  

        SHOW_BOOT_PROGRESS ();  

        if ((hdr->ih_os != IH_OS_LINUX) ||
            (hdr->ih_arch != IH_CPU_ARM) ||
            (hdr->ih_type != IH_TYPE_RAMDISK)) {
            printf ("No Linux ARM Ramdisk Image\n");
            SHOW_BOOT_PROGRESS (-);
            do_reset (cmdtp, flag, argc, argv);
        }  

#if defined(CONFIG_B2) || defined(CONFIG_EVB4510) || defined(CONFIG_ARMADILLO)
        /*
         *we need to copy the ramdisk to SRAM to let Linux boot
         */
        memmove ((void *) ntohl(hdr->ih_load), (uchar *)data, len);
        data = ntohl(hdr->ih_load);
#endif /* CONFIG_B2 || CONFIG_EVB4510 */  

        /*
         * Now check if we have a multifile image
         */
    } else if ((hdr->ih_type == IH_TYPE_MULTI) && (len_ptr[])) {
        ulong tail = ntohl (len_ptr[]) % ;
        int i;  

        SHOW_BOOT_PROGRESS ();  

        /* skip kernel length and terminator */
        data = (ulong) (&len_ptr[]);
        /* skip any additional image length fields */
        for (i = ; len_ptr[i]; ++i)
            data += ;
        /* add kernel length, and align */
        data += ntohl (len_ptr[]);
        if (tail) {
            data +=  - tail;
        }  

        len = ntohl (len_ptr[]);  

    } else {
        /*
         * no initrd image
         */
        SHOW_BOOT_PROGRESS ();  

        len = data = ;
    }  

#ifdef  DEBUG
    if (!data) {
        printf ("No initrd\n");
    }
#endif  

    if (data) {
        initrd_start = data;
        initrd_end = initrd_start + len;
    } else {
        initrd_start = ;
        initrd_end = ;
    }  

    SHOW_BOOT_PROGRESS ();  

    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);设置各种tag，用于传递参数给Linux
#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 (initrd_start && initrd_end)
        setup_initrd_tag (bd, initrd_start, initrd_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");打印信息  

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

    cleanup_before_linux ();启动之前先做一些清理工作cpu/arm920t/cpu.c  

调用内核需要传递的参数如下：
R0：必须为0
R1：机器类型ID，本机为ARM（bd->bi_arch_number）
R2：启动参数列表在内存中的位置（bd->bi_boot_params）
    theKernel (, bd->bi_arch_number, bd->bi_boot_params);
}  

3.1设置标记ATAG_CORE

标记列表以标记ATAG_CORE开始

static void setup_start_tag (bd_t *bd)
{
    params = (struct tag *) bd->bi_boot_params;  

    params->hdr.tag = ATAG_CORE;
    params->hdr.size = tag_size (tag_core);  

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

    params = tag_next (params);//指向当前标记的末尾
}  

 

3.2设置内存标记ATAG_MEM

在board/smdk2410/smdk2410.c的dram_init函数设置了bd的bi_dram结构体：

int dram_init (void)
{
    gd->bd->bi_dram[].start = PHYS_SDRAM_1;
    gd->bd->bi_dram[].size = PHYS_SDRAM_1_SIZE;  

    return ;
}  

下面是这边内存标记的结构体：

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

    for (i = ; i < CONFIG_NR_DRAM_BANKS; i++) {
        params->hdr.tag = ATAG_MEM;
        params->hdr.size = tag_size (tag_mem32);  

        params->u.mem.start = bd->bi_dram[i].start;
        params->u.mem.size = bd->bi_dram[i].size;  

        params = tag_next (params);
    }
}  

 

3.3设置命令行标记ATAG_CMDLINE

命令行就是一个字符串，用来控制内核的一些行为。比如“root=/dev/mtdblock2 init=/linuxrc console=ttySAC0 ”表示根文件系统在MTD2分区上系统启动后执行的第一个程序为/linuxrc，控制台是ttySAC0 。

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;
    params->hdr.size =
        (sizeof (struct tag_header) + strlen (p) +  + ) >> ;  

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

    params = tag_next (params);
}  

 

3.4设置ATAG_NONE

标记列表以标记ATAG_NONE介绍。