OK3399-C开机不久调试串口失效是为什么？如何解决？

OK3399-C开机不久调试串口失效，暂时未接屏幕，应该修改内核的哪个文件？

最后打印信息：
INFO: sleep mode config[0xde]:
INFO:          AP_PWROFF
INFO:          SLP_ARMPD
INFO:          SLP_PLLPD
INFO:          DDR_RET
INFO:          SLP_CENTER_PD
INFO: wakeup source config[0x804]:
INFO:          GPIO interrupt can wakeup system
INFO:          PWM interrupt can wakeup system
INFO: PWM CONFIG[0x4]:
INFO:          PWM: PWM2D_REGULATOR_EN
INFO: APIOS info[0x0]:
INFO:          not config
INFO: GPIO POWER INFO:
INFO:          GPIO1_C1
INFO:          GPIO1_B6
INFO: PMU_MODE_CONG: 0x1477bf51