[U-Boot] Disable tftp and access

Hello,

I want to disable uboot tftp on my device and if uboot allow some login/access(eg. by console) then disable it too.

My aim is to lock uboot except booting image(OS), I want manage it only from OS(changing env variables only from OS)

I want to ask what env variables I should change to disable tftp functions and access?

Thanks, Kubco