CM5/Pi5: CPU hotplug broken - CPU_ON fails after CPU_OFF (PSCI)

[gtstud]

Describe the bug

Description:

• After taking a CPU offline via /sys/devices/system/cpu/cpuN/online
• Bringing it back online fails with error -22
• dmesg shows: "psci: failed to boot CPU1 (-22)"
• Same failure occurs after kexec when target kernel tries CPU_ON
• Only cold boot resets the PSCI state machine

Impact:

• CPU hotplug is non-functional
• kexec to new kernel fails to bring up secondary CPUs

Hardware: Raspberry Pi CM5

Steps to reproduce the behaviour

on root shell, do:
echo 0>/sys/devices/system/cpu/cpu1/online
echo 1>/sys/devices/system/cpu/cpu1/online

Device (s)

Raspberry Pi CM5 Lite

System

(! 518)-> cat /etc/rpi-issue
Raspberry Pi reference 2025-12-04
Generated using pi-gen, https://github.com/RPi-Distro/pi-gen, 4997bf4e4e49bc3305eb182a4a08bd023529da04, stage4

(! 519)-> vcgencmd version
2025/12/08 19:29:54
Copyright (c) 2012 Broadcom
version 2226a853 (release) (embedded)

(! 520)-> uname -a
Linux scorscion 6.12.75+rpt-rpi-2712 #1 SMP PREEMPT Debian 1:6.12.75-1+rpt1 (2026-03-11) aarch64 GNU/Linux

Logs

[ 1654.502987] psci: CPU1 killed (polled 0 ms)
[ 1677.441585] CPU1: failed to come online
[ 1677.445450] CPU1: failed in unknown state : 0x0
[ 1772.549796] psci: failed to boot CPU1 (-22)
[ 1772.549806] CPU1: failed to boot: -22

Additional context

No response

[timg236]

Has this ever worked on CM5?

There is only one power domain for the CPUs, so you can't actually switch an individual core off. IIRC the VC firmware support only exists to support S2RAM in the (far) future.

[gtstud]

I have no idea - I was trying to use zfsbootmenu on the CM5 and got that problem when ZBM was kexec-ing the target system kernel...