Lower CPU frequency on imx8mm

[daisukeyoshinar]

Hello

I am using the latest release 4.9.98_2.0.0 on iMX 8M Mini EVK.
I want to set the CPU frequency lower than 400MHz.

I changed dtis file.

~/imx-yocto-bsp/build-xwayland/tmp/work-shared/imx8mmevk/kernel-source/arch/arm64/boot/dts/freescale/fsl-imx8mm.dtis

&A53_0 {
    operating-points = <
        /* kHz    uV */
        1800000 1000000
        1600000 950000
        1500000 950000
        1300000 950000
        1200000 850000
        1000000 850000
        800000 850000
        600000 850000
        400000 850000
        200000 850000
        100000 850000
        10000 850000
    >;

Twelve operating points are recognized.

root@imx8mmevk:/sys/devices/system/cpu/cpu0/cpufreq# cat scaling_available_frequencies
10000 100000 200000 400000 600000 800000 1000000 1200000 1300000 1500000 1600000 1800000

Switching from 1.8GHz to 600MHz is possible.
However, the following error occurs when the frequency is set to 400 MHz or lower.

root@imx8mmevk:/sys/devices/system/cpu/cpu0/cpufreq# echo 400000 > scaling_setspeed
[ 2553.146119] cpu cpu0: failed to set clock rate: -16
[ 2553.339631] cpufreq: __target_index: Failed to change cpu frequency: -16

Where can I change it to 400MHz or lower?

In addition, when I made the same change and used the IMX8MQ-evk board, I confirmed that it can be set to 400MHz or less.

Best regards,
Daisuke Yoshinari

[Bio_TICFSL · Accepted solution]

Hello Daisuke,

This patch from the BSP team, which adds the lower frequency points to the MX8MM.

This is the note that came along with it:

"The 8MQ and 8MM uses different PLL, the 8MM’s 1416 PLL does NOT have 400MHz in rate table; here is a patch for it."

Regards

[gnulux]

Hello , 

Does this patch can be applied to IMXM Plus SOC  too ? 

Rgds

[daisukeyoshinar]

Thank you very much for your reply.

After applying the patch, it became 400MHz or less.

Best regards,
Daisuke Yoshinari