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How can I change CPU frequency on i.MX6Q ?

Question asked by Nicolas Said on Sep 29, 2016
Latest reply on Oct 20, 2016 by Artur Petukhov

Hello,

 

I'm currently facing a minor issue while developing on a MX6Q... We have a GPS receiver installed near the MX6 board running Yocto Fido, and it seems that as it's running most of the time at 792MHz, it generates EM perturbations (harmonics @ 1.584GHz) which lies inside the GPS L1 band... We believe that avoiding this particular CPU frequency would solve our EM pollution problem. Reading the dts (imx6q-var-dart.dts), it seems that multiple operating frequencies are available:

&cpu0 {
         operating-points = <
            /* kHz    uV */
            1200000 1350000
            996000  1250000
            852000  1250000
            792000  1175000
            396000  1175000
         >;
         fsl,soc-operating-points = <
            /* ARM kHz  SOC-PU uV */
            1200000 1275000
            996000   1250000
            852000   1250000
            792000   1175000
            396000   1175000
         >;
};
Also, one weird fact is that, while using cpufreq-info, the only two frequencies I get listed are 396 MHz and 792 MHz, as shown below:
analyzing CPU 0:
driver: imx6q-cpufreq
CPUs which run at the same hardware frequency: 0 1 2 3
CPUs which need to have their frequency coordinated by software: 0 1 2 3
maximum transition latency: 61.0 us.
hardware limits: 396 MHz - 792 MHz
available frequency steps: 396 MHz, 792 MHz
available cpufreq governors: conservative, ondemand, userspace, powersave, interactive, performance
current policy: frequency should be within 396 MHz and 792 MHz.
The governor "interactive" may decide which speed to use
within this range.
current CPU frequency is 396 MHz (asserted by call to hardware).
cpufreq stats: 396 MHz:93.00%, 792 MHz:7.00% (2235)


So... How can I disable the 792MHz, and make the board revert to another frequency (preferably higher, like 996MHz or even higher) ?

Thanks in advance.

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