last reboot reason

Hello Friends,

We are using RZ/A1 processor based custom target board . linux kernel version is 4.9.123 ( downloaded from renesas site).
user manual r01uh0403ej0200_rz_a1h pdf is referred .

we need to  identify the processor registers if any to identify the source of reset ((external, watchdog, warm, or cold) . 

could you help us to identify the same  . 

If registers are present , is there any existing driver present in kernel sources which can help us read the values from registers appropriately at next power on ?

Thanks and regards,
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