Lower CPU frequency on imx8mq

[daisukeyoshinar]

Hello,

I am using the latest release 4.9.98_2.0.0 on iMX 8M Quad EVK.

I want to set the CPU frequency lower than 1.0GHz.

I tried to change the dts file with i.MX_Linux Reference_Manual.pdf, but there are 4 operational points already.

~/imx-yocto-bsp/build-xwayland/tmp/work-shared/imx8mqevk/kernel-source/arch/arm64/boot/dts/freescale/fsl-imx8mq-evk.dts
&A53_0 {
   operating-points = <
   /* kHz uV */
   1500000 1000000
   1300000 1000000
   1000000 900000
   800000 900000
   >;
   dc-supply = <&reg_gpio_dvfs>;
};

I confirmed that the EVK board is using this dts.
root@imx8mqevk:/proc/device-tree# strings compatible
fsl,imx8mq-evk
fsl,imx8mq

The operating point is displayed as follows.
root@imx8mqevk:/proc/device-tree/cpus/cpu@0# hexdump -C operating-points
00000000 00 16 e3 60 00 0f 42 40 00 13 d6 20 00 0f 42 40 |...`..B@... ..B@|
00000010 00 0f 42 40 00 0d bb a0 00 0c 35 00 00 0d bb a0 |..B@......5.....|

0x16e360 -> 1500000(1.5GHz)
0x13d620 -> 1300000(1.3GHz)
0xf4240 -> 1000000(1.0GHz)
0xdbba0 -> 900000(900MHz)
0xc3500 -> 800000(800MHz)

However, only two operating points in the governor are displayed.
root@imx8mqevk:/sys/devices/system/cpu/cpu0/cpufreq# cat scaling_available_frequencies
1000000 1500000

Also, the minimum clock cannot be set lower than 1.0GHz.

Where should I change to add an operating point?

Best regards,
Yoshinari.

[igorpadykov · Accepted solution]

Hi Yoshinari

these operating points are for both industrial and consumer gardes, while

consumer grade supports only 1.GHz, 1.5GHz according to Table 7. Operating ranges

i.MX 8M Dual / 8M QuadLite / 8M Quad Applications Processors Data Sheet for Consumer Products

industrial grade supports only 800MHz, 1.3GHz according to Table 7. Operating ranges

i.MX 8M Dual / 8M QuadLite / 8M Quad Applications Processors Data Sheet for Industrial Products

>Where should I change to add an operating point?

for other frequencies one will have to modify cpufreq driver described in sect.2.3.3.2.1 Source Code Structure

attached Linux Manual.

Best regards
igor
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[yhegde]

Hi @igorpadykov,

Are you saying that it is possible to create our own operating points which can be of a frequency below the frequencies mentioned in the data sheet by adding to the OPP tables in the correct dtsi file in arch/arm/boot/dts? Or do we modify the actual NXP cpufreq driver in the correct imx*-cpufreq.c file to create some custom frequency? Is that even possible? For example, if on my i.MX8DXP the only available frequencies in cpufreq are 900000 kHZ and 1200000 kHz, how can I create a setting to go even lower?

[daisukeyoshinar]

Thank you for quick reply.

The operating point was disabled by grade.
/imx8mqevk/kernel-source/drivers/soc/imx/soc-imx8.c

After changing, it became 800MHz.

Best regards,
Daisuke Yoshinari