You can refer to the efuse usage on uboot command.
kvim2#efuse
efuse - efuse commands
Usage:
efuse [read/write offset size [data]]
[read/wirte] - read or write 'size' data from
'offset' from efuse user data ;
[offset] - the offset byte from the beginning
of efuse user data zone;
[size] - data size
[data] - the optional argument for 'write',
data is treated as characters
examples: efuse write 0xc 0xd abcdABCD1234
[amlogic_set addr]
I write the mac address 98:3E:2B:23:34:56 into OTP with efuse command. The data size is 12.
kvim2#efuse write 0x0 0xc 983E2B233456
Yes, the efuse is for old amlogic serial CPU. But we can use it to save mac address.
The OTP(CPU Ram) can only be written once. You should write the key into emmc when you want to erase or overwrite these memories.