移植Linux-3.4.2内核到S3C2440

一、BootLoader引导内核过程     1、Bootloader的工作
    1.1、将内核读入内存     2.2、保存内核启动参数到指定位置,内核启动时去这个位置解析参数     3.3、启动内核、传入机器ID
二、内核的启动流程         内核首要目的是挂载根文件系统,启动应用程序,内核启动的过程大致为以下几步:
1.检查CPU和机器类型 2.进行堆栈、MMU等其他程序运行关键的东西进行初始化 3.打印内核信息 4.执行各种模块的初始化 5.挂接根文件系统 6.启动第一个init进程
对于ARM的处理器,内核第一个启动的文件是arc/arm/kernel下面的head.S文件 第一阶段: 首先截取部分head.S文件
ENTRY(stext)

 THUMB(    adr    r9, BSYM(1f)    )    @ Kernel is always entered in ARM.
 THUMB(    bx    r9        )    @ If this is a Thumb-2 kernel,
 THUMB(    .thumb            )    @ switch to Thumb now.
 THUMB(1:            )

    setmode    PSR_F_BIT | PSR_I_BIT | SVC_MODE, r9 @ ensure svc mode
                        @ and irqs disabled
    mrc    p15, 0, r9, c0, c0        @ get processor id
    bl    __lookup_processor_type        @ r5=procinfo r9=cpuid
    movs    r10, r5                @ invalid processor (r5=0)?
 THUMB( it    eq )        @ force fixup-able long branch encoding
    beq    __error_p            @ yes, error 'p'

#ifdef CONFIG_ARM_LPAE
    mrc    p15, 0, r3, c0, c1, 4        @ read ID_MMFR0
    and    r3, r3, #0xf            @ extract VMSA support
    cmp    r3, #5                @ long-descriptor translation table format?
 THUMB( it    lo )                @ force fixup-able long branch encoding
    blo    __error_p            @ only classic page table format
#endif
View Code 第一步,执行的是__lookup_processor_type,这个函数是检查处理器型号,它读取你的板子的CPU型号与内核支持的处理器进行比较看是否能够处理。 第二步,检查机器型号,它会读取你bootloader传进来的机器ID和他能够处 理的机器ID进行比较看是否能够处理。内核的ID号定义在arc/arm/tool/mach_types文件中MACH_TYPE_xxxx宏定义。内 核究竟就如何检查是否是它支持的机器的呢?实际上每个机器都会在/arc/arm/mach-xxxx/smdk-xxxx.c文件中有个描述特定机器的 数据结构,
MACHINE_START(S3C2440, "SMDK2440")
    /* Maintainer: Ben Dooks <ben-linux@fluff.org> */
    .atag_offset    = 0x100,

    .init_irq    = s3c24xx_init_irq,
    .map_io        = smdk2440_map_io,
    .init_machine    = smdk2440_machine_init,
    .timer        = &s3c24xx_timer,
    .restart    = s3c244x_restart,
MACHINE_END
View Code

MACHINE_START和 MACHINE_END实际上被展开成一个结构体

#defineMACHINE_START(_type,_name)                 \  
staticconst struct machine_desc __mach_desc_##_type       \  
 __used                                             \  
 __attribute__((__section__(".arch.info.init")))= {    \  
       .nr          =MACH_TYPE_##_type,           \  
       .name             =_name,  
        
#defineMACHINE_END                          \  
};  
View Code

于是上面的数据结构就被展开为

staticconst struct machine_desc __mach_desc_S3C2440     \  
 __used                                             \  
 __attribute__((__section__(".arch.info.init")))= {    \  
       .nr          =MACH_TYPE_S3C2440,          \  
       .name             =”SMDK2440”,};  
.phys_io  = S3C2410_PA_UART,  
       .io_pg_offst    = (((u32)S3C24XX_VA_UART) >> 18) & 0xfffc,  
       .boot_params  = S3C2410_SDRAM_PA + 0x100,  
   
       .init_irq   =s3c24xx_init_irq,  
       .map_io          =smdk2440_map_io,  
       .init_machine  = smdk2440_machine_init,  
       .timer             =&s3c24xx_timer,  
   
}  
View Code 每个机器都会有一个machine_desc__mach_desc结构,内核通过检查每个machine_desc__mach_desc的nr 号和bootloader传上来的ID进行比较,如果相同,内核就认为支持该机器,而且内核在后面的工作中会调用该机器的 machine_desc__mach_desc_结构中的方法进行一些初始化工作。 第三步,创建一级页表 第四步,在R13中保存__switch_data 这个函数的地址,在第四步使能mmu完成后会跳到该函数执行。 第五步,执行的是__enable_mmu,它是使能MMU,这个函数调用了__turn_mmu_on函数,让后在_turn_mmu_on在最 后将第三步赋给R13的值传给了PC指针 (mov    pc, r13),于是内核开始跳到__switch_data这个函数开始执行。 我们再来看arch/arm/kenel/head-common.S这个文件中的__switch_data函数
/*
 * The following fragment of code is executed with the MMU on in MMU mode,
 * and uses absolute addresses; this is not position independent.
 *
 *  r0  = cp#15 control register
 *  r1  = machine ID
 *  r2  = atags/dtb pointer
 *  r9  = processor ID
 */
    __INIT
__mmap_switched:
    adr    r3, __mmap_switched_data

    ldmia    r3!, {r4, r5, r6, r7}
    cmp    r4, r5                @ Copy data segment if needed
1:    cmpne    r5, r6
    ldrne    fp, [r4], #4
    strne    fp, [r5], #4
    bne    1b

    mov    fp, #0                @ Clear BSS (and zero fp)
1:    cmp    r6, r7
    strcc    fp, [r6],#4
    bcc    1b

 ARM(    ldmia    r3, {r4, r5, r6, r7, sp})
 THUMB(    ldmia    r3, {r4, r5, r6, r7}    )
 THUMB(    ldr    sp, [r3, #16]        )
    str    r9, [r4]            @ Save processor ID
    str    r1, [r5]            @ Save machine type
    str    r2, [r6]            @ Save atags pointer
    bic    r4, r0, #CR_A            @ Clear 'A' bit
    stmia    r7, {r0, r4}            @ Save control register values
    b    start_kernel
ENDPROC(__mmap_switched)

    .align    2
    .type    __mmap_switched_data, %object
__mmap_switched_data:
    .long    __data_loc            @ r4
    .long    _sdata                @ r5
    .long    __bss_start            @ r6
    .long    _end                @ r7
    .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
    .size    __mmap_switched_data, . - __mmap_switched_data
View Code 这个函数做的工作是,复制数据段清楚BBS段,设置堆在指针,然后保存处理器内核和机器内核等工作,最后跳到start_kernel函数。于是内核开始执行第二阶段。 第二阶段: init/目录下的main.c的start_kernel函数
asmlinkage void __init start_kernel(void)
在start_kernel首先是打印内核信息,然后对bootloader传进来的一些参数进行处理,再接着执行各种各样的初始化,在这其中会初始化控制台。最后会调用rest_init(); 我们再来看rest_init()函数
static noinline void __init_refok rest_init(void)

他启动了kernel_init这个函数,再来看kerne_init函数

static int __init kernel_init(void * unused)
{
    /*
     * Wait until kthreadd is all set-up.
     */
    wait_for_completion(&kthreadd_done);

    /* Now the scheduler is fully set up and can do blocking allocations */
    gfp_allowed_mask = __GFP_BITS_MASK;

    /*
     * init can allocate pages on any node
     */
    set_mems_allowed(node_states[N_HIGH_MEMORY]);
    /*
     * init can run on any cpu.
     */
    set_cpus_allowed_ptr(current, cpu_all_mask);

    cad_pid = task_pid(current);

    smp_prepare_cpus(setup_max_cpus);

    do_pre_smp_initcalls();
    lockup_detector_init();

    smp_init();
    sched_init_smp();

    do_basic_setup();

    /* Open the /dev/console on the rootfs, this should never fail */
    if (sys_open((const char __user *) "/dev/console", O_RDWR, 0) < 0)
        printk(KERN_WARNING "Warning: unable to open an initial console.\n");

    (void) sys_dup(0);
    (void) sys_dup(0);
    /*
     * check if there is an early userspace init.  If yes, let it do all
     * the work
     */

    if (!ramdisk_execute_command)
        ramdisk_execute_command = "/init";

    if (sys_access((const char __user *) ramdisk_execute_command, 0) != 0) {
        ramdisk_execute_command = NULL;
        prepare_namespace();
    }

    /*
     * Ok, we have completed the initial bootup, and
     * we're essentially up and running. Get rid of the
     * initmem segments and start the user-mode stuff..
     */

    init_post();
    return 0;
}
View Code kernel_init先调用了prepare_namespace();然后调用了init_post函数 在prepare_namespace()函数里 调用mount_root()函数,挂载根文件系统; 三、移植linux3.4.2到JZ2440 1、解压tar xjf linux-3.4.2.tar.bz2 2、进入解压后的文件目录,修改顶层Makefile vim Makefile   修改架构为 ARM 以及编译器
     ARCH=arm
     CROSS_COMPILE=arm-linux-

3、选择默认配置

find -name"*defconfig"

4、在解压后文件目录下,配置,生成.config文件

make s3c2410_defconfig

5、查看支持的单板

vim .config

6、编译

make uImage

7、u-boot2012里默认的是193机器ID,设置机器ID为362使用SMDK2440,在uboot中设置机器ID

set machid 16a
save

8、在uboot中设置启动行参数并修改smdk2440单板的晶振信息12M

bootargs noinitrd root=/dev/nfs nfsroot=192.168.1.112:/opt/filesystem ip=192.168.1.130:192.168.1.112:192.168.1.1:255,255,255,0::eth0:off init=/linuxrc console=ttySAC0,115200

修改文件mach-smdk2440.c的晶振信息12M

static void __init smdk2440_map_io(void)
{
    s3c24xx_init_io(smdk2440_iodesc, ARRAY_SIZE(smdk2440_iodesc));
    s3c24xx_init_clocks(12000000);
    s3c24xx_init_uarts(smdk2440_uartcfgs, ARRAY_SIZE(smdk2440_uartcfgs));
}
四、修改分区 我们经常用的内核打印分区信息如下
Creating 4 MTD partitions on "NAND":
0x000000000000-0x000000040000 : "bootloader"
0x000000040000-0x000000060000 : "params"
0x000000060000-0x000000460000 : "kernel"
0x000000460000-0x000010000000 : "rootfs"

这些分区是通过在文件linux-2.6.22.6\arch\arm\plat-s3c24xx/Common-smdk.c设置的

/* NAND parititon from 2.4.18-swl5 */

static struct mtd_partition smdk_default_nand_part[] = {
    [0] = {
        .name    = "bootloader",
        .size    = SZ_256K,
        .offset    = 0,
    },
    [1] = {
        .name    = "params",
        .offset = MTDPART_OFS_APPEND,
        .size    = SZ_128K,
    },
    [2] = {
        .name    = "kernel",
        .offset = MTDPART_OFS_APPEND,
        .size    = SZ_4M,
    },
    [3] = {
        .name    = "rootfs",
        .offset    = MTDPART_OFS_APPEND,
        .size    = MTDPART_SIZ_FULL,
    },
};
五、添加网卡驱动 修改arch/arm/mach-s3c24xx/mach-smdk2440.c     1 添加头文件#include <linux/dm9000.h>     2 网卡基地址 
#define MACH_SMDK2440_DM9K_BASE (S3C2410_CS4 + 0x300)

 3 添加资源和设备

/* DM9000AEP 10/100 ethernet controller */

static struct resource smdk2440_dm9k_resource[] = {
    [0] = {
        .start = MACH_SMDK2440_DM9K_BASE,
        .end   = MACH_SMDK2440_DM9K_BASE + 3,
        .flags = IORESOURCE_MEM
    },
    [1] = {
        .start = MACH_SMDK2440_DM9K_BASE + 4,
        .end   = MACH_SMDK2440_DM9K_BASE + 7,
        .flags = IORESOURCE_MEM
    },
    [2] = {
        .start = IRQ_EINT7,
        .end   = IRQ_EINT7,
        .flags = IORESOURCE_IRQ | IORESOURCE_IRQ_HIGHEDGE,
    }
};


/*
 * The DM9000 has no eeprom, and it's MAC address is set by
 * the bootloader before starting the kernel.
 */
static struct dm9000_plat_data smdk2440_dm9k_pdata =http://www.cnblogs.com/Ye-Jason/p/ {
    .flags        = (DM9000_PLATF_16BITONLY | DM9000_PLATF_NO_EEPROM),
};

static struct platform_device smdk2440_device_eth = {
    .name        = "dm9000",
    .id        = -1,
    .num_resources    = ARRAY_SIZE(smdk2440_dm9k_resource),
    .resource    = smdk2440_dm9k_resource,
    .dev        = {
        .platform_data    = &smdk2440_dm9k_pdata,
    },
};


static struct platform_device *smdk2440_devices[] __initdata =http://www.cnblogs.com/Ye-Jason/p/ {
    &s3c_device_ohci,
    &s3c_device_lcd,
    &s3c_device_wdt,
    &s3c_device_i2c0,
    &s3c_device_iis,
    &smdk2440_device_eth,
};
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 综上,make uImage 完成Linux3.4.2的移植,并添加了网卡驱动。

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