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

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Date:   Tue, 5 Dec 2017 16:26:29 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Meelis Roos <mroos@...ee>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        Rafael Wysocki <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        "4 . 14+" <stable@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpufreq: longhaul: Set transition_delay_us to 20 ms

On Tue, Dec 5, 2017 at 9:54 AM, Meelis Roos <mroos@...ee> wrote:
>> > 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.

OK, so can you please try to modify the patch to set
transition_delay_us to 30000, say, and see if that's reliable?

Thanks,
Rafael