Power down an individual i.MX95 core from Linux?

[JustSomeGuyOnTheInternet]

I'm interested in fully powering down specific mx95 cores but the options I have tried so far do not seem to work:

- maxcpus=1 in uboot

- taking cores offline e.g. using /sys/devices/system/cpu/cpu?/online

I see there might be support using SCMI to do this but it's not clear to me yet how to exercise this from Linux and it doesn't seem to be happening automagically from the options above.

Any suggestions please or do I need to start digging through kernel and scmi source code?

Thank you!

[JustSomeGuyOnTheInternet]

Hi

Yes, I want to power down one or more of the A cores.

After limiting the cores with say maxcpus=1 in uboot the other cores are indeed shown as offline as expected:

root@imx95:~# cat /sys/devices/system/cpu/cpu?/online

1

0

0

0

0

0

However the cores appear to still be powered as per the output below. Also there is no improvement in operating temperature - I would expect at least some improvement from powering down the cores.  Unfortunately I'm not set up to measure current consumption to confirm this at the moment hence I'm using the temperature and this power domain status as an indicator of success:

root@imx95:~# cat /sys/kernel/debug/pm_genpd/a55c?/current_state

on

on

on

on

on

on 

[yipingwang]

I discussed with the AE team.

The A55 core0 will be powerup by default and Linux will manage the rest of the A55 cores. You could assure to disable the specific core by using command "echo 0 > /sys/devices/system/cpu/cpuX/online". Commonly, the power consumption and the operating temperature won't be different after power down some A cores unless there are massive loading on the CPU.

[yipingwang]

Do you want to power down specific A core on  i.MX95 platform?

You could use the two methods mentioned by you.

For example:

root@imx95evk:~# echo 0 > /sys/devices/system/cpu/cpu4/online

root@imx95evk:~# echo 0 > /sys/devices/system/cpu/cpu5/online

What problem did you encounter?