the timestamp during the kernel boot not correct

I set the frequency of the system counter to 20MHz: by set cntfrq_el0

dmesg:

arch_timer_of_init, rate 20000000

arch_timer: cp15 timer(s) running at 20.00MHz (phys).

but in dmesg, the time shows take 10 seconds to finish the boot,

but in fact, it is 3 mins which I count by my iphone.

does anyone can tell the reason?

since it is a arm board, I can't get the cpu freq though /proc/cpuinfo, 

processor : 0
BogoMIPS : 40.00
Features : fp asimd evtstrm crc32 cpuid
CPU implementer : 0x41
CPU architecture: 8
CPU variant : 0x0
CPU part : 0xd03
CPU revision : 4

Hardware : Rockchip RK3568 EVB1 DDR4 V10 Board
Serial : 0000000000000000