R3 mini can not boot from nand

Hello, everyone, my R3 mini can’t be started from nand. Now emmc have the offcial openwrt, I want to burn a new frimware to nand, but when I try to run

mtd erase /dev/mtd

and then show

Could not open /dev/mtd device: device 0

It seems that I can’t do anything about nand. Is there any way to solve it?