从start_kernel到开发板初始化

从start_kernel到开发板初始化

-->//板子上电启动后进入start_kernel( )
    start_kernel( )
        -->setup_arch(&command_line)
        //command_line由内核传入
            -->mdesc = setup_machine(machine_arch_type);
                -->list = lookup_machine_type(nr);
                //汇编实现查找机器码所定义的平台，找到后返回mdesc结构
            -->init_machine = mdesc->init_machine;
            //struct machine_desc *mdesc;machine_desc结构很重要，在saar.c中定义此结构
            //machine_arch_type机器码，在UBOOT有定义，内核中也有定义定义
        -->rest_init()
            -->kernel_thread(kernel_init, NULL, CLONE_FS | CLONE_SIGHAND);
            //定义进程kernel_init，此进程pid=1，会在kthreadd进程创建好后调度运行
                -->kernel_init()
                    -->do_basic_setup()
                        -->driver_init()
                            -->devices_init()
                            -->buses_init()
                            -->classes_init()
                            -->platform_bus_init()
                        -->do_initcalls()
                        //此函数很重要，执行了initcall表中所有的函数，包含了init_machine（saar_init()）函数
                            -->saar_init()
                    -->init_post()
                    //调度用户空间程序，比如bash，在用户空间死循环执行程序
            -->pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES);
            //定义进程kthreadd

/******************start_kernel() @ /init/main.c *************************/

asmlinkage void __init start_kernel(void)
{
    char * command_line;
    extern 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();
    cgroup_init_early();

    local_irq_disable();
    early_boot_irqs_off();
    early_init_irq_lock_class();

/*
 * Interrupts are still disabled. Do necessary setups, then
 * enable them
 */
    lock_kernel();
    tick_init();
    boot_cpu_init();
    page_address_init();
    printk(KERN_NOTICE);
    printk(linux_banner);
    setup_arch(&command_line);
    mm_init_owner(&init_mm, &init_task);
    setup_command_line(command_line);
    setup_per_cpu_areas();
    setup_nr_cpu_ids();
    smp_prepare_boot_cpu();    /* arch-specific boot-cpu hooks */

    /*
     * Set up the scheduler prior starting any interrupts (such as the
     * timer interrupt). Full topology setup happens at smp_init()
     * time - but meanwhile we still have a functioning scheduler.
     */
    sched_init();
    /*
     * Disable preemption - early bootup scheduling is extremely
     * fragile until we cpu_idle() for the first time.
     */
    preempt_disable();
    build_all_zonelists();
    page_alloc_init();
    printk(KERN_NOTICE "Kernel command line: %s\n", boot_command_line);
    parse_early_param();
    parse_args("Booting kernel", static_command_line, __start___param,
           __stop___param - __start___param,
           &unknown_bootoption);
    if (!irqs_disabled()) {
        printk(KERN_WARNING "start_kernel(): bug: interrupts were "
                "enabled *very* early, fixing it\n");
        local_irq_disable();
    }
    sort_main_extable();
    trap_init();
    rcu_init();
    /* init some links before init_ISA_irqs() */
    early_irq_init();
    init_IRQ();
    pidhash_init();
    init_timers();
    hrtimers_init();
    softirq_init();
    timekeeping_init();
    time_init();
    sched_clock_init();
    profile_init();
    if (!irqs_disabled())
        printk(KERN_CRIT "start_kernel(): bug: interrupts were "
                 "enabled early\n");
    early_boot_irqs_on();
    local_irq_enable();

    /*
     * HACK  This is early. We're enabling the console before
     * we've done PCI setups etc, and console_init() must be aware of
     * this. But we do want output early, in case something goes wrong.
     */
    console_init();
    if (panic_later)
        panic(panic_later, panic_param);

    lockdep_info();

    /*
     * Need to run this when irqs are enabled, because it wants
     * to self-test [hard/soft]-irqs on/off lock inversion bugs
     * too:
     */
    locking_selftest();

#ifdef CONFIG_BLK_DEV_INITRD
    if (initrd_start && !initrd_below_start_ok &&
        page_to_pfn(virt_to_page((void *)initrd_start)) < min_low_pfn) {
        printk(KERN_CRIT "initrd overwritten (0x%08lx < 0x%08lx) - "
            "disabling it.\n",
            page_to_pfn(virt_to_page((void *)initrd_start)),
            min_low_pfn);
        initrd_start = 0;
    }
#endif
    vmalloc_init();
    vfs_caches_init_early();
    cpuset_init_early();
    page_cgroup_init();
    mem_init();
    enable_debug_pagealloc();
    cpu_hotplug_init();
    kmem_cache_init();
    debug_objects_mem_init();
    idr_init_cache();
    setup_per_cpu_pageset();
    numa_policy_init();
    if (late_time_init)
        late_time_init();
    calibrate_delay();
    pidmap_init();
    pgtable_cache_init();
    prio_tree_init();
    anon_vma_init();
#ifdef CONFIG_X86
    if (efi_enabled)
        efi_enter_virtual_mode();
#endif
    thread_info_cache_init();
    cred_init();
    fork_init(num_physpages);
    proc_caches_init();
    buffer_init();
    key_init();
    security_init();
    vfs_caches_init(num_physpages);
    radix_tree_init();
    signals_init();
    /* rootfs populating might need page-writeback */
    page_writeback_init();
#ifdef CONFIG_PROC_FS
    proc_root_init();
#endif
    cgroup_init();
    cpuset_init();
    taskstats_init_early();
    delayacct_init();

    check_bugs();

    acpi_early_init(); /* before LAPIC and SMP init */

    ftrace_init();

    /* Do the rest non-__init'ed, we're now alive */
    rest_init();
}
/******************start_kernel()    end   **********************/

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

    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;

    memcpy(boot_command_line, from, COMMAND_LINE_SIZE);
    boot_command_line[COMMAND_LINE_SIZE-1] = '\0';
    parse_cmdline(cmdline_p, from);
    paging_init(mdesc);
    request_standard_resources(&meminfo, mdesc);

#ifdef CONFIG_SMP
    smp_init_cpus();
#endif

    cpu_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();
}

static int __init kernel_init(void * unused)
{
    lock_kernel();
    /*
     * init can run on any cpu.
     */
    set_cpus_allowed_ptr(current, CPU_MASK_ALL_PTR);
    /*
     * Tell the world that we're going to be the grim
     * reaper of innocent orphaned children.
     *
     * We don't want people to have to make incorrect
     * assumptions about where in the task array this
     * can be found.
     */
    init_pid_ns.child_reaper = current;

    cad_pid = task_pid(current);

    smp_prepare_cpus(setup_max_cpus);

    do_pre_smp_initcalls();
    start_boot_trace();

    smp_init();
    sched_init_smp();

    cpuset_init_smp();

    do_basic_setup();

    /*
     * 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;
}

static void __init do_basic_setup(void)
{
    rcu_init_sched(); /* needed by module_init stage. */
    init_workqueues();
    usermodehelper_init();
    driver_init();
    init_irq_proc();
    do_initcalls();
}

void __init driver_init(void)
{
    /* These are the core pieces */
    devices_init();
    buses_init();
    classes_init();
    firmware_init();
    hypervisor_init();

    /* These are also core pieces, but must come after the
     * core core pieces.
     */
    platform_bus_init();
    system_bus_init();
    cpu_dev_init();
    memory_dev_init();
}

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static void __init do_initcalls(void)
{
    initcall_t *call;

    for (call = __early_initcall_end; call < __initcall_end; call++)
        do_one_initcall(*call);

    /* Make sure there is no pending stuff from the initcall sequence */
    flush_scheduled_work();
}

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static noinline int init_post(void)
{
    /* need to finish all async __init code before freeing the memory */
    async_synchronize_full();
    free_initmem();
    unlock_kernel();
    mark_rodata_ro();
    system_state = SYSTEM_RUNNING;
    numa_default_policy();

    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);

    current->signal->flags |= SIGNAL_UNKILLABLE;

    if (ramdisk_execute_command) {
        run_init_process(ramdisk_execute_command);
        printk(KERN_WARNING "Failed to execute %s\n",
                ramdisk_execute_command);
    }

    /*
     * We try each of these until one succeeds.
     *
     * The Bourne shell can be used instead of init if we are
     * trying to recover a really broken machine.
     */
    if (execute_command) {
        run_init_process(execute_command);
        printk(KERN_WARNING "Failed to execute %s.  Attempting "
                    "defaults...\n", execute_command);
    }
    run_init_process("/sbin/init");
    run_init_process("/etc/init");
    run_init_process("/bin/init");
    run_init_process("/bin/sh");

    panic("No init found.  Try passing init= option to kernel.");
}

MACHINE_START(SAAR, "PXA930 handheld Platform (SAAR)")
    .phys_io        = 0x40000000,
    .boot_params    = 0xa0000100,
    .io_pg_offst    = (io_p2v(0x40000000) >> 18) & 0xfffc,
    .map_io         = pxa_map_io,
    .init_irq       = pxa3xx_init_irq,
    .timer          = &pxa_timer,
    .init_machine   = saar_init,
MACHINE_END


#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                \
};



static void (*init_machine)(void) __initdata;

static int __init customize_machine(void)
{
    /* customizes platform devices, or adds new ones */
    if (init_machine)
        init_machine();
    return 0;
}
arch_initcall(customize_machine);



#define __define_initcall(level,fn,id) \
    static initcall_t __initcall_##fn##id __used \
    __attribute__((__section__(".initcall" level ".init"))) = fn

/*
 * Early initcalls run before initializing SMP.
 *
 * Only for built-in code, not modules.
 */
#define early_initcall(fn)        __define_initcall("early",fn,early)

/*
 * A "pure" initcall has no dependencies on anything else, and purely
 * initializes variables that couldn't be statically initialized.
 *
 * This only exists for built-in code, not for modules.
 */
#define pure_initcall(fn)        __define_initcall("0",fn,0)

#define core_initcall(fn)        __define_initcall("1",fn,1)
#define core_initcall_sync(fn)        __define_initcall("1s",fn,1s)
#define postcore_initcall(fn)        __define_initcall("2",fn,2)
#define postcore_initcall_sync(fn)    __define_initcall("2s",fn,2s)
#define arch_initcall(fn)        __define_initcall("3",fn,3)
#define arch_initcall_sync(fn)        __define_initcall("3s",fn,3s)
#define subsys_initcall(fn)        __define_initcall("4",fn,4)
#define subsys_initcall_sync(fn)    __define_initcall("4s",fn,4s)
#define fs_initcall(fn)            __define_initcall("5",fn,5)
#define fs_initcall_sync(fn)        __define_initcall("5s",fn,5s)
#define rootfs_initcall(fn)        __define_initcall("rootfs",fn,rootfs)
#define device_initcall(fn)        __define_initcall("6",fn,6)
#define device_initcall_sync(fn)    __define_initcall("6s",fn,6s)
#define late_initcall(fn)        __define_initcall("7",fn,7)
#define late_initcall_sync(fn)        __define_initcall("7s",fn,7s)

#define __initcall(fn) device_initcall(fn)

#define __exitcall(fn) \
    static exitcall_t __exitcall_##fn __exit_call = fn

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);
    if (!list) {
        printk("Machine configuration botched (nr %d), unable "
               "to continue.\n", nr);
        while (1);
    }

    printk("Machine: %s\n", list->name);

    return list;
}