linux-kernel - Re: [PATCH] cpufreq: longhaul: Set transition_delay

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Date:   Tue, 5 Dec 2017 10:54:57 +0200 (EET)
From:   Meelis Roos <mroos@...ee>
To:     Viresh Kumar <viresh.kumar@...aro.org>
cc:     Rafael Wysocki <rjw@...ysocki.net>, linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        "4 . 14+" <stable@...r.kernel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cpufreq: longhaul: Set transition_delay_us to 20 ms

> > The commit e948bc8fbee0 ("cpufreq: Cap the default transition delay
> > value to 10 ms") caused a regression on EPIA-M min-ITX computer where
> > shutdown or reboot hangs occasionally with a print message like:
> > 
> > longhaul: Warning: Timeout while waiting for idle PCI bus
> > cpufreq: __target_index: Failed to change cpu frequency: -16
> > 
> > This probably happens because the cpufreq governor tries to change the
> > frequency of the CPU faster than allowed by the hardware.
> > 
> > With the above commit, the default transition delay comes to 10 ms for a
> > transition_latency of 200 us. Set the default transition delay to 20 ms
> > directly to fix this regression.
> > 
> > Fixes: e948bc8fbee0 ("cpufreq: Cap the default transition delay value to 10 ms")
> > Cc: 4.14+ <stable@...r.kernel.org> # 4.14+
> > Reported-by: Meelis Roos <mroos@...ux.ee>
> > Suggested-by: Rafael J. Wysocki <rjw@...ysocki.net>
> > Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> > ---
> >  drivers/cpufreq/longhaul.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/cpufreq/longhaul.c b/drivers/cpufreq/longhaul.c
> > index c46a12df40dd..56eafcb07859 100644
> > --- a/drivers/cpufreq/longhaul.c
> > +++ b/drivers/cpufreq/longhaul.c
> > @@ -894,7 +894,7 @@ static int longhaul_cpu_init(struct cpufreq_policy *policy)
> >  	if ((longhaul_version != TYPE_LONGHAUL_V1) && (scale_voltage != 0))
> >  		longhaul_setup_voltagescaling();
> >  
> > -	policy->cpuinfo.transition_latency = 200000;	/* nsec */
> > +	policy->transition_delay_us = 20000;	/* usec */
> >  
> >  	return cpufreq_table_validate_and_show(policy, longhaul_table);
> >  }
> 
> This patch also works on my EPIA-M board - tested 10+ times.

An on the last try just after sending the mail, it hung again in the 
same way as before - so maybe 20 is on the edge of being good.


-- 
Meelis Roos (mroos@...ee)      http://www.cs.ut.ee/~mroos/