RK3288: missing processor serial number at cpuinfo file after kernel compilation on tinkerboard

[santosmjc]

Armbianmonitor:

http://ix.io/2jQR

Hi,

I installed "Armbian_20.02.7_Tinkerboard_buster_current_5.4.28_minimal" at my tinkerboard and, in order to enable uart 4, I had to rebuild the kernel onboard (from linux-source-current-rockchip_20.02.7_all.deb).

The uart 4 came alive but the processor serial number now is missing from cpuinfo (printing 0000000000). How can I bring  it up again?