kernel since 5.6 do not boot anymore on Apple PowerBook

[Giuseppe Sacco]

Hello Christophe,

Il giorno mer, 26/08/2020 alle 15.53 +0200, Christophe Leroy ha
scritto:
[...]
> If there is no warning, then the issue is something else, bad luck.
> 
> Could you increase the loglevel and try again both with and without 
> VMAP_STACK ? Maybe we'll get more information on where it stops.

The problem is related to the CPU frequency changes. This is where the
system stop: cpufreq get the CPU frequency limits and then start the
default governor (performance) and then calls function
cpufreq_gov_performance_limits() that never returns.

Rebuilding after enabling pr_debug for cpufreq.c, I've got some more
lines of output:

cpufreq: setting new policy for CPU 0: 667000 - 867000 kHz
cpufreq: new min and max freqs are 667000 - 867000 kHz
cpufreq: governor switch
cpufreq: cpufreq_init_governor: for CPU 0
cpufreq: cpufreq_start_governor: for CPU 0
cpufreq: target for CPU 0: 867000 kHz, relation 1, requested 867000 kHz
cpufreq: __target_index: cpu: 0, oldfreq: 667000, new freq: 867000
cpufreq: notification 0 of frequency transition to 867000 kHz
cpufreq: saving 133328 as reference value for loops_per_jiffy; freq is 667000 kHz

no more lines are printed. I think this output only refers to the
notification sent prior to the frequency change.

I was thinking that selecting a governor that would run at 667mHz would
probably skip the problem. I added cpufreq.default_governor=powersave
to the command line parameters but it did not work: the selected
governor was still performance and the system crashed.

Bye,
Giuseppe