[REGRESSION] cpuidle: psci: boot stall/hang on i.MX8MP

[Dario Binacchi]

Hi Ulf,

on an i.MX8M Plus Dual board (Engicam i.Core MX8M Plus), mainline
c339f4010dea sometimes stalls for ~0.9 s at boot, or hangs until the
watchdog resets the board, right after:

  [    0.806123] ledtrig-cpu: registered to indicate activity on CPUs

On a good boot the next message comes ~11 ms later.

About 1 boot out of 3 stalls or hangs. With cpuidle.off=1, or
with commit 65705b18162b ("cpuidle: psci: Move initialization a bit
earlier in the boot sequence") reverted, 10 out of 10 boots are fine.

I haven't dug into it much. The stall seems to be in
pl330_driver_init(), so my guess is that it is related to the AMBA bus
reading the ID registers of the CoreSight ETMs while a CPU is already
in cpu_pd_wait, but I may well be wrong.

Any idea?

#regzbot introduced: 65705b18162b

Thanks,
Dario