android系统重启流程分析

1.reboot命令实现

./kernel/arch/alpha/kernel/setup.c:void __init setup_arch(char **cmdline_p){...if (mdesc->restart_mode)        reboot_setup(&mdesc->restart_mode);...if (mdesc->restart)        arm_pm_restart = mdesc->restart;...}./mediatek/platform/mt6572/kernel/core/core.c:MACHINE_START(MT6572, "MT6572")    .atag_offset    = 0x00000100,    .map_io         = mt_map_io,    .init_irq       = mt_init_irq,    .timer          = &mt6572_timer,    .init_machine   = mt_init,    .fixup          = mt_fixup,    .restart        = arm_machine_restart,    .reserve        = mt_reserve,MACHINE_END./kernel/arch/arm/kernel/process.c:void arm_machine_restart(char mode, const char *cmd){...arch_reset(mode, cmd);...}./mediatek/kernel/kernel/system.c:void arch_reset(char mode, const char *cmd){    char reboot = 0;    int res=0;    struct wd_api*wd_api = NULL;    res = get_wd_api(&wd_api);    printk("arch_reset: cmd = %s\n", cmd ? : "NULL");    if (cmd && !strcmp(cmd, "charger")) {        /* do nothing */    } else if (cmd && !strcmp(cmd, "recovery")) {        rtc_mark_recovery();    } else if (cmd && !strcmp(cmd, "bootloader")){            rtc_mark_fast();        } #ifdef MTK_KERNEL_POWER_OFF_CHARGING    else if (cmd && !strcmp(cmd, "kpoc")){        rtc_mark_kpoc();    }#endif    else {        reboot = 1;        //printk("rtc_mark_powerkey\n");//zhanglei add        //rtc_mark_powerkey();//zhanglei add    }    if(res){        printk("arch_reset, get wd api error %d\n",res);    } else {        wd_api->wd_sw_reset(reboot);    }}arch_reset根据上层传的命令执行不同的动作，最后执行wd_sw_reset(reboot)。./mediatek/kernel/drivers/wdk/wd_api.c:static int wd_sw_reset(int type){   wdt_arch_reset(type);   return 0;}./mediatek/platform/mt6572/kernel/drivers/wdt/mtk_wdt.c:void wdt_arch_reset(char mode){...DRV_WriteReg32(MTK_WDT_RESTART, MTK_WDT_RESTART_KEY);...}从上可以产出系统重启动作是通过看门狗完成的，如果关闭IPO（快速开关机功能）后，系统重启动作会导致系统完全掉电，内核关闭，看门狗无法正常工作，从而导致系统无法重启。

2.开机boot_mode_check

preloader:./mediatek/platform/mt6572/preloader/src/drivers/platform.c:void platform_init(void){...g_boot_reason = reason = platform_boot_status();...}static boot_reason_t platform_boot_status(void){...#if defined (MTK_KERNEL_POWER_OFF_CHARGING)    ulong begin = get_timer(0);    do  {        if (rtc_boot_check()) {            print("%s RTC boot!\n", MOD);            return BR_RTC;        }        if(!kpoc_flag)            break;    } while (get_timer(begin) < 1000 && kpoc_flag);#else    if (rtc_boot_check()) {        print("%s RTC boot!\n", MOD);        return BR_RTC;    }#endif...}./mediatek/platform/mt6572/preloader/src/drivers/mt_rtc.c:bool rtc_boot_check(void){...if ((pdn1 & 0x0030) == 0x0010) {    /* factory data reset */        /* keep bit 4 set until rtc_boot_check() in U-Boot */        return true;    }    //zhanglei add    if (pdn1 & 0x0080) {    /*  power on  time */        /* keep bit 7 set until rtc_boot_check() in U-Boot */        return true;    }#if defined (MTK_KERNEL_POWER_OFF_CHARGING)    if ((pdn1 & 0x4000) == 0x4000) {           kpoc_flag = true;        return false;    }#endif    return false;}通过判断pdn1寄存器的标志位返回是否是真正的启动状态。lk:./mediatek/platform/mt6572/lk/platform.c:void platform_init(void){...#ifndef CFG_POWER_CHARGING    /* NOTE: if define CFG_POWER_CHARGING, will rtc_boot_check() in mt65xx_bat_init() */    rtc_boot_check(false);#endif...}./mediatek/platform/mt6572/lk/mt_rtc.c:bool rtc_boot_check(bool can_alarm_boot){...    if ((pdn1 & RTC_PDN1_RECOVERY_MASK) == RTC_PDN1_FAC_RESET) {    /* factory data reset */        RTC_Write(RTC_PDN1, pdn1 & ~RTC_PDN1_FAC_RESET);        rtc_write_trigger();        return true;    }    if (pdn1 & 0x0040) {    /* bypass power key detection */        RTC_Write(RTC_PDN1, pdn1 & ~0x0040);        rtc_write_trigger();        return true;    }    //zhanglei add    if (pdn1 & 0x0080) {    /*  power on  time */        /* keep bit 7 set until rtc_boot_check() in U-Boot */        return true;    }    return false;...}原理同preloader层。