Deciding what frequency within the CPUfreq policy should be used is achieved using "cpufreq governors".
Inside the CPUFreq we can find:
# ls /sys/devices/system/cpu/cpu1/cpufreq/
# cat /sys/devices/system/cpu/cpu1/cpufreq/scaling_available_frequencies
2400000 2133000 1867000 1600000
The cpu OPP(frequencies and voltages) should be defined by silicon vendor, then the OPP table will defined in dts file and pass to cpufreq driver in linux kernel. You can't add arbitrary OPP to cpufreq. Even if you tweak dts file to add more OPP to cpufreq driver, it will not work to change the real frequency.