kernel since 5.6 do not boot anymore on Apple PowerBook

[Giuseppe Sacco]

Il giorno gio, 27/08/2020 alle 09.46 +0200, Giuseppe Sacco ha scritto:
> Il giorno gio, 27/08/2020 alle 00.28 +0200, Giuseppe Sacco ha scritto:
> > 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.
> 
> I kept following the thread and found that CPU frequency is changed in
> function pmu_set_cpu_speed() in file drivers/cpufreq/pmac32-cpufreq.c.
> As first thing, the function calls the macro preempt_disable() and this
> is where it stops.

Sorry, I made a mistake. The real problem is down, on the same
function, when it calls low_sleep_handler(). This is where the problem
probably is.

Bye,
Giuseppe