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/ affected_cpus related_cpus scaling_max_freq bios_limit scaling_available_frequencies scaling_min_freq cpuinfo_cur_freq scaling_available_governors scaling_setspeed cpuinfo_max_freq scaling_cur_freq stats cpuinfo_min_freq scaling_driver cpuinfo_transition_latency scaling_governor
scaling_available_frequencies
# 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.