Why is 7ULP EVK SOM not entering CPUIdle Wait and Stop modes ?

[jcolafrancesco]

Hello,
I'm testing the 7ULP EVK board. Only powering the SOM though USB-C.

Current distribution 4.9.88-imx_4.9.88_2.0.0_ga+g5e23f9d

Potentially, the A7 processor should enter WFI, PSTOP2 (Wait) or PSTOP1 (Stop) when the system goes idle.

Actually, only WFI mode seems to be used, with only superficial power saving.

I can see we are not entering the other power saving mode because :

Power top indicate 0% in WAIT and STOP modes.

And also 

cat /sys/devices/system/cpu/cpu0/cpuidle/state0/usage

Shows a big positive value whereas 

cat /sys/devices/system/cpu/cpu0/cpuidle/state1/usage

and

cat /sys/devices/system/cpu/cpu0/cpuidle/state2/usage

both shows 0.

Any idea of what may impeach the system to use the deeper idle state modes ?

[igorpadykov]

Hi Julien

L4.9.88 is very old kernel, recommended to use at least L4.14.98 and follow AN12573

i.MX 7ULP Power Consumption Measurement

L4.14.98_2.0.0_LINUX_DOCS

Measuring Current in i.MX Applications

Best regards
igor
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[jcolafrancesco]

Thanks, I'm now using 4.19.35 and i observe the same behavior.

[ZeeFrench]

Hello Julien,

When linux is idle, CA7 goes to wfi mode but you need to send a command to go in stop mode.

echo freeze > /sys/power/state

and then wake up from CM4 console with "W" (if you have flashed a QSPI firmware) or push on/off button of EVK, you will have spent some time in cpuidle/state2.

Apparently, nothing is mapped to intermediate cpuidle/state1 though, at least not the further low power state, standby and mem.

Best regards, Philippe.