android 9 reboot流程

机器出现开机自动进入fastboot模式。可能是init 那个进程挂了然后调用了
RebootSystem(ANDROID_RB_RESTART2, “bootloader”); 函数进入重启流程，然后重启后进入fastboot
浅读一下reboot流程和怎么进入的fastboot
比如说是那个进程挂了调用了这个函数，然后就是会调用到 RebootSystem
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在查看一下RebootSystem(unsigned int cmd, const std::string& rebootTarget)的paramete
paramete 1 :cmd 就是 reboot 命令是poweroff 还是restart
paramete 2: rebootTarget 就是重启的参数只有restart才会用到这个参数（reboot recovery/bootloader）重启后进入指定模式例如fastboot
recovery模式
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看重启流程：
syscall是一个系统调用在这调用_NR_reboot指令
系统调用之后就是进入内核
include\linux\syscall.h 中调用SYSCALL_DEFINE4 因为 _NR_reboot后面带4个参数实际
SYSCALL_DEFINE4会根据你的命令（reboot star stop 等一下关于内核的命令调用实际函数）
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就是这个name
-------------------------分界线---------------
比如_NR_reboot 就是调用sys_reboot函数，其他exit或者shutdown同理

那么我们就在内核中调用了sys_reboot并且系统层给了参数
asmlinkage long sys_reboot(int magic1, int magic2, unsigned int cmd, void __user *arg);
syscall(__NR_reboot, LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2,LINUX_REBOOT_CMD_RESTART2, rebootTarget.c_str()
对应就是 magic1 = LINUX_REBOOT_MAGIC1
magic2 =LINUX_REBOOT_MAGIC2
cmd = LINUX_REBOOT_CMD_RESTART2(重启）
rebootTarget.c_str() = 重启参数在开头给的是“bootloder”
--------------------------分界线-------------------------------------------
分界线内的说明好像不正确，他不是调用的sys_reboot函数，而是把函数重新定义
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实际调用的还是SYSCALL_DEFINE4(name ,arg…)
reboot: SYSCALL_DEFINE4(reboot ,arg…)

kernel-4.9/kernel/reboot.c中
SYSCALL_DEFINE4(reboot, int, magic1, int, magic2, unsigned int, cmd,void __user *, arg)
{struct pid_namespace *pid_ns = task_active_pid_ns(current);char buffer[256];int ret = 0;/* We only trust the superuser with rebooting the system. */if (!ns_capable(pid_ns->user_ns, CAP_SYS_BOOT))return -EPERM;/* For safety, we require "magic" arguments. */if (magic1 != LINUX_REBOOT_MAGIC1 ||(magic2 != LINUX_REBOOT_MAGIC2 &&magic2 != LINUX_REBOOT_MAGIC2A &&magic2 != LINUX_REBOOT_MAGIC2B &&magic2 != LINUX_REBOOT_MAGIC2C))return -EINVAL;/** If pid namespaces are enabled and the current task is in a child* pid_namespace, the command is handled by reboot_pid_ns() which will* call do_exit().*/ret = reboot_pid_ns(pid_ns, cmd);if (ret)return ret;/* Instead of trying to make the power_off code look like* halt when pm_power_off is not set do it the easy way.*/if ((cmd == LINUX_REBOOT_CMD_POWER_OFF) && !pm_power_off)cmd = LINUX_REBOOT_CMD_HALT;mutex_lock(&reboot_mutex);switch (cmd) {case LINUX_REBOOT_CMD_RESTART:kernel_restart(NULL);break;case LINUX_REBOOT_CMD_CAD_ON:C_A_D = 1;break;case LINUX_REBOOT_CMD_CAD_OFF:C_A_D = 0;break;case LINUX_REBOOT_CMD_HALT:kernel_halt();do_exit(0);panic("cannot halt");case LINUX_REBOOT_CMD_POWER_OFF:kernel_power_off();do_exit(0);break;case LINUX_REBOOT_CMD_RESTART2:ret = strncpy_from_user(&buffer[0], arg, sizeof(buffer) - 1);if (ret < 0) {ret = -EFAULT;break;}buffer[sizeof(buffer) - 1] = '\0';kernel_restart(buffer);break;#ifdef CONFIG_KEXEC_COREcase LINUX_REBOOT_CMD_KEXEC:ret = kernel_kexec();break;
#endif#ifdef CONFIG_HIBERNATIONcase LINUX_REBOOT_CMD_SW_SUSPEND:ret = hibernate();break;
#endifdefault:ret = -EINVAL;break;}mutex_unlock(&reboot_mutex);return ret;
}

如果走重启流程调用：kernel_restart(buffer);

void kernel_restart(char *cmd)
{kernel_restart_prepare(cmd);migrate_to_reboot_cpu();syscore_shutdown();if (!cmd)pr_emerg("Restarting system\n");elsepr_emerg("Restarting system with command '%s'\n", cmd);kmsg_dump(KMSG_DUMP_RESTART);machine_restart(cmd);
}

调用 machine_restart(cmd)
kernel4.9/arch/arm/kernel/reboot.c
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调用do_kernel_restart

void do_kernel_restart(char *cmd)
{atomic_notifier_call_chain(&restart_handler_list, reboot_mode, cmd);
}

atomic_notifier_call_chain做的是向注册restart_handler_list的驱动发送一个通知，通知各个通过register_restart_handler注册的钩子函数，执行这个关机函数
在kernel4.9/drivers/watchdog_core.c
__watchdog_register_device函数中注册
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调用：watchdog_restart_notifier

调用：wdd->ops->restart(wdd, action, data);
看一下restart的实现在哪里
mtk_wdt.c

static int mtk_reset_handler(struct notifier_block *this, unsigned long mode,void *cmd)
{struct mtk_wdt_dev *mtk_wdt;void __iomem *wdt_base;u32 reg;mtk_wdt = container_of(this, struct mtk_wdt_dev, restart_handler);wdt_base = mtk_wdt->wdt_base;/** WDT_STATUS will be cleared to  zero after writing to WDT_MODE, so we backup it in WDT_NONRST_REG,* and then print it out in mtk_wdt_probe() after reset*/writel(__raw_readl(wdt_base + WDT_STATUS), wdt_base + WDT_NONRST_REG);reg = ioread32(wdt_base + WDT_MODE);reg &= ~(WDT_MODE_DUAL_EN | WDT_MODE_IRQ_EN | WDT_MODE_EN);reg |= WDT_MODE_KEY;iowrite32(reg, wdt_base + WDT_MODE);if (cmd && (strcmp(cmd, "rpmbpk") == 0)) {iowrite32(ioread32(wdt_base + WDT_NONRST_REG2) | (1U << 0), wdt_base + WDT_NONRST_REG2);} else if (cmd && (strcmp(cmd, "recovery") == 0)) {iowrite32(ioread32(wdt_base + WDT_NONRST_REG2) | (1U << 1), wdt_base + WDT_NONRST_REG2);#ifdef CONFIG_MT6397_MISCmtk_misc_mark_recovery();#endif} else if (cmd && (strcmp(cmd, "bootloader") == 0)) {iowrite32(ioread32(wdt_base + WDT_NONRST_REG2) | (1U << 2), wdt_base + WDT_NONRST_REG2);#ifdef CONFIG_MT6397_MISCmtk_misc_mark_fast();#endif} else {//do nothing}if (!arm_pm_restart) {while (1) {writel(WDT_SWRST_KEY, wdt_base + WDT_SWRST);mdelay(5);}}return NOTIFY_DONE;
}

这里就是resart实现的地方，那么我们传下来的参数是bootloader
iowrite32(ioread32(wdt_base + WDT_NONRST_REG2) | (1U << 2), wdt_base + WDT_NONRST_REG2);
看到这是写看了一个寄存器，这要看数据手册才知道写的是那个寄存器了，不过在lk阶段就是判断RTC的寄存器来判断进入fasterboot模式的。
vendor\mediatek\proprietary\bootable\bootloader\lk\platform\mt8163\boot_mode.c

void boot_mode_select(void)
{int factory_forbidden = 0;//  int forbid_mode;
/*We put conditions here to filer some cases that can not do key detection*/extern int kedump_mini(void) __attribute__((weak));if (kedump_mini){if (kedump_mini()){mrdump_check();return;}}if (meta_detection()){return;}mrdump_check();#if defined (HAVE_LK_TEXT_MENU)
/*Check RTC to know if system want to reboot to Fastboot*/if(Check_RTC_PDN1_bit13()){dprintf(CRITICAL, "[FASTBOOT] reboot to boot loader\n");g_boot_mode = FASTBOOT;Set_Clr_RTC_PDN1_bit13(false);return;}/*If forbidden mode is factory, cacel the factory key detection*/if(g_boot_arg->sec_limit.magic_num == 0x4C4C4C4C){if(g_boot_arg->sec_limit.forbid_mode == F_FACTORY_MODE){//Forbid to enter factory modedprintf(CRITICAL, "%s Forbidden\n",MODULE_NAME);factory_forbidden=1;}}//  forbid_mode = g_boot_arg->boot_mode &= 0x000000FF;/*If boot reason is power key + volumn down, thendisable factory mode dectection*/if(mtk_detect_pmic_just_rst()){factory_forbidden=1;}/*Check RTC to know if system want to reboot to Recovery*/if(Check_RTC_Recovery_Mode()){g_boot_mode = RECOVERY_BOOT;return;}/*If MISC Write has not completed  in recovery modebefore system reboot, go to recovery mode tofinish remain tasks*/if(unshield_recovery_detection()){return;}ulong begin = get_timer(0);/*we put key dectection here to detect key which is pressed*/