struct cpu_operations {
    const char    *name;
    int        (*cpu_init)(unsigned int);  读取必要的数据准备初始化。
    int        (*cpu_prepare)(unsigned int);  启动前准备工作
    int        (*cpu_boot)(unsigned int);  启动一个CPU
    void        (*cpu_postboot)(void);  执行boot后的清理工作
#ifdef CONFIG_HOTPLUG_CPU
    int        (*cpu_disable)(unsigned int cpu);  关闭CPU之前的准备工作
    void        (*cpu_die)(unsigned int cpu);  关闭CPU
    int        (*cpu_kill)(unsigned int cpu);  确认是否关闭
#endif
#ifdef CONFIG_CPU_IDLE
    int        (*cpu_init_idle)(unsigned int);  读取CPU idle状态的参数
    int        (*cpu_suspend)(unsigned long);  suspend一个CPU，并且保存上下文
#endif
};

static int __init smp_cpu_setup(int cpu)
{
    if (cpu_read_ops(cpu))
        return -ENODEV;

    if (cpu_ops[cpu]->cpu_init(cpu))
        return -ENODEV;

    set_cpu_possible(cpu, true);

    return 0;
}

void __init smp_prepare_cpus(unsigned int max_cpus)
{
    int err;
    unsigned int cpu, ncores = num_possible_cpus();

    init_cpu_topology();  填充cpu_topology结构体数组

    smp_store_cpu_info(smp_processor_id());

    /*
     * are we trying to boot more cores than exist?
     */
    if (max_cpus > ncores)  不能超过possible cpu数目
        max_cpus = ncores;

    /* Don‘t bother if we‘re effectively UP */
    if (max_cpus <= 1)
        return;

    /*
     * Initialise the present map (which describes the set of CPUs
     * actually populated at the present time) and release the
     * secondaries from the bootloader.
     *
     * Make sure we online at most (max_cpus - 1) additional CPUs.
     */
    max_cpus--;
    for_each_possible_cpu(cpu) {
        if (max_cpus == 0)
            break;

        if (cpu == smp_processor_id())
            continue;

        if (!cpu_ops[cpu])
            continue;

        err = cpu_ops[cpu]->cpu_prepare(cpu);  执行.cpu_prepare回调函数，将指定cpu设置为present。
        if (err)
            continue;

        set_cpu_present(cpu, true);
        max_cpus--;
    }
}

static int boot_secondary(unsigned int cpu, struct task_struct *idle)
{
    if (cpu_ops[cpu]->cpu_boot)
        return cpu_ops[cpu]->cpu_boot(cpu);

    return -EOPNOTSUPP;
}

asmlinkage void secondary_start_kernel(void)
{
    struct mm_struct *mm = &init_mm;
    unsigned int cpu = smp_processor_id();

    /*
     * All kernel threads share the same mm context; grab a
     * reference and switch to it.
     */
    atomic_inc(&mm->mm_count);
    current->active_mm = mm;

    set_my_cpu_offset(per_cpu_offset(smp_processor_id()));

    /*
     * TTBR0 is only used for the identity mapping at this stage. Make it
     * point to zero page to avoid speculatively fetching new entries.
     */
    cpu_set_reserved_ttbr0();
    local_flush_tlb_all();
    cpu_set_default_tcr_t0sz();

    preempt_disable();
    trace_hardirqs_off();

    /*
     * If the system has established the capabilities, make sure
     * this CPU ticks all of those. If it doesn‘t, the CPU will
     * fail to come online.
     */
    verify_local_cpu_capabilities();

    if (cpu_ops[cpu]->cpu_postboot)
        cpu_ops[cpu]->cpu_postboot();

    /*
     * Log the CPU info before it is marked online and might get read.
     */
    cpuinfo_store_cpu();

    /*
     * Enable GIC and timers.
     */
    notify_cpu_starting(cpu);

    smp_store_cpu_info(cpu);

    /*
     * OK, now it‘s safe to let the boot CPU continue.  Wait for
     * the CPU migration code to notice that the CPU is online
     * before we continue.
     */
    pr_info("CPU%u: Booted secondary processor [%08x]\n",
                     cpu, read_cpuid_id());
    set_cpu_online(cpu, true);
    complete(&cpu_running);

    local_dbg_enable();
    local_irq_enable();
    local_async_enable();

    /*
     * OK, it‘s off to the idle thread for us
     */
    cpu_startup_entry(CPUHP_ONLINE);
}

static int op_cpu_disable(unsigned int cpu)
{
    /*
     * If we don‘t have a cpu_die method, abort before we reach the point
     * of no return. CPU0 may not have an cpu_ops, so test for it.
     */
    if (!cpu_ops[cpu] || !cpu_ops[cpu]->cpu_die)
        return -EOPNOTSUPP;

    /*
     * We may need to abort a hot unplug for some other mechanism-specific
     * reason.
     */
    if (cpu_ops[cpu]->cpu_disable)
        return cpu_ops[cpu]->cpu_disable(cpu);

    return 0;
}

void cpu_die(void)
{
    unsigned int cpu = smp_processor_id();

    idle_task_exit();

    local_irq_disable();

    /* Tell __cpu_die() that this CPU is now safe to dispose of */
    (void)cpu_report_death();

    /*
     * Actually shutdown the CPU. This must never fail. The specific hotplug
     * mechanism must perform all required cache maintenance to ensure that
     * no dirty lines are lost in the process of shutting down the CPU.
     */
    cpu_ops[cpu]->cpu_die(cpu);

    BUG();
}

static int op_cpu_kill(unsigned int cpu)
{
    /*
     * If we have no means of synchronising with the dying CPU, then assume
     * that it is really dead. We can only wait for an arbitrary length of
     * time and hope that it‘s dead, so let‘s skip the wait and just hope.
     */
    if (!cpu_ops[cpu]->cpu_kill)
        return 0;

    return cpu_ops[cpu]->cpu_kill(cpu);
}

int __init arm_cpuidle_init(unsigned int cpu)
{
    int ret = -EOPNOTSUPP;

    if (cpu_ops[cpu] && cpu_ops[cpu]->cpu_init_idle)
        ret = cpu_ops[cpu]->cpu_init_idle(cpu);

    return ret;
}

int arm_cpuidle_suspend(int index)
{
    int cpu = smp_processor_id();

    /*
     * If cpu_ops have not been registered or suspend
     * has not been initialized, cpu_suspend call fails early.
     */
    if (!cpu_ops[cpu] || !cpu_ops[cpu]->cpu_suspend)
        return -EOPNOTSUPP;
    return cpu_ops[cpu]->cpu_suspend(index);
}

int __init cpu_read_ops(int cpu)
{
    const char *enable_method = cpu_read_enable_method(cpu);  从DeviceTree获取enable_method字符串

    if (!enable_method)
        return -ENODEV;

    cpu_ops[cpu] = cpu_get_ops(enable_method);  根据enable_method字符串在supported_cpu_ops获取指针
    if (!cpu_ops[cpu]) {
        pr_warn("Unsupported enable-method: %s\n", enable_method);
        return -EOPNOTSUPP;
    }

    return 0;
}

static const struct cpu_operations *supported_cpu_ops[] __initconst = {
    &smp_spin_table_ops,
    &cpu_psci_ops,
    NULL,
};

const struct cpu_operations cpu_psci_ops = {
    .name        = "psci",
#ifdef CONFIG_CPU_IDLE
    .cpu_init_idle    = cpu_psci_cpu_init_idle,  从DeviceTree获取CPU idle状态数据
    .cpu_suspend    = cpu_psci_cpu_suspend,  根据是否丢失上下文来选择是psci_ops.cpu_suspend还是cpu_suspend
#endif
    .cpu_init    = cpu_psci_cpu_init,  为空
    .cpu_prepare    = cpu_psci_cpu_prepare,  只是判断psci_ops.cpu_on是否存在，不存在则返回错误。
    .cpu_boot    = cpu_psci_cpu_boot,  调用psci_ops.cpu_on
#ifdef CONFIG_HOTPLUG_CPU
    .cpu_disable    = cpu_psci_cpu_disable,  检查是否支持psci_ops.cpu_off。
    .cpu_die    = cpu_psci_cpu_die,  调用psci_ops.cpu_off
    .cpu_kill    = cpu_psci_cpu_kill,  检查指定cpu是否已经被kill
#endif
}

static int cpu_psci_cpu_boot(unsigned int cpu)
{
    int err = psci_ops.cpu_on(cpu_logical_map(cpu), __pa(secondary_entry));
    if (err)
        pr_err("failed to boot CPU%d (%d)\n", cpu, err);

    return err;
}

ENTRY(secondary_entry)
    bl    el2_setup            // Drop to EL1
    bl    set_cpu_boot_mode_flag
    b    secondary_startup
ENDPROC(secondary_entry)

ENTRY(secondary_startup)
    /*
     * Common entry point for secondary CPUs.
     */
    adrp    x25, idmap_pg_dir
    adrp    x26, swapper_pg_dir
    bl    __cpu_setup            // initialise processor

    ldr    x21, =secondary_data
    ldr    x27, =__secondary_switched    // address to jump to after enabling the MMU
    b    __enable_mmu
ENDPROC(secondary_startup)

ENTRY(__secondary_switched)
    ldr    x0, [x21]            // get secondary_data.stack
    mov    sp, x0
    mov    x29, #0
    b    secondary_start_kernel
ENDPROC(__secondary_switched)

static int __maybe_unused cpu_psci_cpu_init_idle(unsigned int cpu)
{
    int i, ret, count = 0;
    u32 *psci_states;
    struct device_node *state_node, *cpu_node;

    cpu_node = of_get_cpu_node(cpu, NULL);
    if (!cpu_node)
        return -ENODEV;

    /*
     * If the PSCI cpu_suspend function hook has not been initialized
     * idle states must not be enabled, so bail out
     */
    if (!psci_ops.cpu_suspend)
        return -EOPNOTSUPP;

    /* Count idle states */
    while ((state_node = of_parse_phandle(cpu_node, "cpu-idle-states",
                          count))) {
        count++;
        of_node_put(state_node);
    }

    if (!count)
        return -ENODEV;

    psci_states = kcalloc(count, sizeof(*psci_states), GFP_KERNEL);
    if (!psci_states)
        return -ENOMEM;

    for (i = 0; i < count; i++) {
        u32 state;

        state_node = of_parse_phandle(cpu_node, "cpu-idle-states", i);

        ret = of_property_read_u32(state_node,
                       "arm,psci-suspend-param",
                       &state);
        if (ret) {
            pr_warn(" * %s missing arm,psci-suspend-param property\n",
                state_node->full_name);
            of_node_put(state_node);
            goto free_mem;
        }

        of_node_put(state_node);
        pr_debug("psci-power-state %#x index %d\n", state, i);
        if (!psci_power_state_is_valid(state)) {
            pr_warn("Invalid PSCI power state %#x\n", state);
            ret = -EINVAL;
            goto free_mem;
        }
        psci_states[i] = state;
    }
    /* Idle states parsed correctly, initialize per-cpu pointer */
    per_cpu(psci_power_state, cpu) = psci_states;
    return 0;

free_mem:
    kfree(psci_states);
    return ret;
}

static int __maybe_unused cpu_psci_cpu_suspend(unsigned long index)
{
    int ret;
    u32 *state = __this_cpu_read(psci_power_state);  从psci_power_state中读取suspend的state参数。
    /*
     * idle state index 0 corresponds to wfi, should never be called
     * from the cpu_suspend operations
     */
    if (WARN_ON_ONCE(!index))
        return -EINVAL;

    if (!psci_power_state_loses_context(state[index - 1]))
        ret = psci_ops.cpu_suspend(state[index - 1], 0);
    else
        ret = cpu_suspend(index, psci_suspend_finisher);

    return ret;
}

static const struct of_device_id const psci_of_match[] __initconst = {
    { .compatible = "arm,psci",    .data = psci_0_1_init},
    { .compatible = "arm,psci-0.2",    .data = psci_0_2_init},
    { .compatible = "arm,psci-1.0",    .data = psci_0_2_init},
    {},
};

int __init psci_dt_init(void)
{
    struct device_node *np;
    const struct of_device_id *matched_np;
    psci_initcall_t init_fn;

    np = of_find_matching_node_and_match(NULL, psci_of_match, &matched_np);

    if (!np)
        return -ENODEV;

    init_fn = (psci_initcall_t)matched_np->data;
    return init_fn(np);
}

static int __init psci_0_2_init(struct device_node *np)
{
    int err;

    err = get_set_conduit_method(np);  从DeviceTree可知invoke_psci_fn = __invoke_psci_fn_smc

    if (err)
        goto out_put_node;
    /*
     * Starting with v0.2, the PSCI specification introduced a call
     * (PSCI_VERSION) that allows probing the firmware version, so
     * that PSCI function IDs and version specific initialization
     * can be carried out according to the specific version reported
     * by firmware
     */
    err = psci_probe();

out_put_node:
    of_node_put(np);
    return err;
}

static void __init psci_0_2_set_functions(void)
{
    pr_info("Using standard PSCI v0.2 function IDs\n");
    psci_function_id[PSCI_FN_CPU_SUSPEND] =
                    PSCI_FN_NATIVE(0_2, CPU_SUSPEND);
    psci_ops.cpu_suspend = psci_cpu_suspend;

    psci_function_id[PSCI_FN_CPU_OFF] = PSCI_0_2_FN_CPU_OFF;
    psci_ops.cpu_off = psci_cpu_off;

    psci_function_id[PSCI_FN_CPU_ON] = PSCI_FN_NATIVE(0_2, CPU_ON);
    psci_ops.cpu_on = psci_cpu_on;

    psci_function_id[PSCI_FN_MIGRATE] = PSCI_FN_NATIVE(0_2, MIGRATE);
    psci_ops.migrate = psci_migrate;

    psci_ops.affinity_info = psci_affinity_info;

    psci_ops.migrate_info_type = psci_migrate_info_type;

    arm_pm_restart = psci_sys_reset;

    pm_power_off = psci_sys_poweroff;
}

/* int __invoke_psci_fn_smc(u64 function_id, u64 arg0, u64 arg1, u64 arg2) */
ENTRY(__invoke_psci_fn_smc)
    smc    #0
    ret
ENDPROC(__invoke_psci_fn_smc)

void machine_power_off(void)
{
    local_irq_disable();
    smp_send_stop();
    if (pm_power_off)
        pm_power_off();
}

void machine_restart(char *cmd)
{
    /* Disable interrupts first */
    local_irq_disable();
    smp_send_stop();

    /*
     * UpdateCapsule() depends on the system being reset via
     * ResetSystem().
     */
    if (efi_enabled(EFI_RUNTIME_SERVICES))
        efi_reboot(reboot_mode, NULL);

    /* Now call the architecture specific reboot code. */
    if (arm_pm_restart)
        arm_pm_restart(reboot_mode, cmd);
    else
        do_kernel_restart(cmd);

    /*
     * Whoops - the architecture was unable to reboot.
     */
    printk("Reboot failed -- System halted\n");
    while (1);
}