How to use uart or i2c pins as normal gpio in quark-n boards?

Im using Quark-N, a linux board based on allwinner h3. Almost all its pins had been allocated to certain function, and I can not see these ports as gpio in sysfs. I need more gpio pins but not familiar to linux lowlevel programming. I goolged this topic but found nothing helpful.
What should I do or any document I can refer to?