I found a strange issue on my i.MX6ULL board:
There is a MCU connect to CPU with UART3, and UART2 is unused.
Application access ttymxc2 without any problem, and also set "enabled" to "/sys/class/tty/ttymxc2/power/wakeup".
But after suspend to RAM (echo mem > /sys/power/state), ttymxc2 becomes abnormal, I cannot read/write anymore.
And I can see the power consumption during suspend mode is higher than it should be, about 10% increase.
I tried lots of settings (BSP/USB/SAI/GPIOs), and finally I found a solution: set "enabled" to "/sys/class/tty/ttymxc1/power/wakeup".
Even through there is no signal connect to UART2, but it just working: ttymxc2 works fine after waking up, and power consumption is normal.
I am not sure the reason why it happened, but I can reproduce this issue on both SDKs (4.14.78_ga_1.0.0 and 4.14.98_ga_2.0.0)