linux-kernel - Re: [PATCH] thermal: cpu_cooling: Iterate over all CPUs in clip

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Date:	Wed, 8 Jul 2015 09:50:56 +0800
From:	Pi-Cheng Chen <pi-cheng.chen@...aro.org>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Zhang Rui <rui.zhang@...el.com>,
	Eduardo Valentin <edubezval@...il.com>,
	Linaro Kernel Mailman List <linaro-kernel@...ts.linaro.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH] thermal: cpu_cooling: Iterate over all CPUs in clip_cpu
 mask to get frequency table

Hi Viresh,

On Tue, Jul 7, 2015 at 6:27 PM, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> On 01-07-15, 12:13, Pi-Cheng Chen wrote:
>> Sorry for the mistake I made when cherry-picking the patch. Fix and resend
>> again.
>
> You really want above to show up in git logs ?
>
> Any comments like this should be present:
> - in cover-letter
> - OR after the three dashes below ---
> - OR must be followed with a scissors line, like this:
>   --------------8<--------

Thanks for the lesson. :)

>
>> __cpufreq_cooling_register() might fail if some CPU other than first one in
>> clip_cpu mask is present earlier e.g. CPU hotplug. Iterate all CPUs in the mask
>> to handle this case.
>>
>> Signed-off-by: Pi-Cheng Chen <pi-cheng.chen@...aro.org>
>> ---
>>  drivers/thermal/cpu_cooling.c | 9 +++++++--
>>  1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/thermal/cpu_cooling.c b/drivers/thermal/cpu_cooling.c
>> index 6509c61..5e90eb6 100644
>> --- a/drivers/thermal/cpu_cooling.c
>> +++ b/drivers/thermal/cpu_cooling.c
>> @@ -776,9 +776,14 @@ __cpufreq_cooling_register(struct device_node *np,
>>       char dev_name[THERMAL_NAME_LENGTH];
>>       struct cpufreq_frequency_table *pos, *table;
>>       unsigned int freq, i, num_cpus;
>> -     int ret;
>> +     int ret, cpu;
>> +
>> +     for_each_cpu(cpu, clip_cpus) {
>> +             table = cpufreq_frequency_get_table(cpu);
>> +             if (table)
>> +                     break;
>> +     }
>>
>> -     table = cpufreq_frequency_get_table(cpumask_first(clip_cpus));
>
> Nah, that's wrong. I hope that's a hypothetical problem and not a real
> one. Would have been better if cpufreq maintainers were cc'd as they
> can provide more insight into this :)
>
> cpufreq_frequency_get_table() does: policy->freq_table and so it
> doesn't matter if the cpu is online or not.
>
> cpufreq_cpu_data was getting unset earlier on hotplug, but that's not
> the case anymore. So nothing to worry about :)

Yes. This is based on the case before 4.2-rc1 which policy of cpu will
be destroy after all cpus in a cluster are unplugged (right?). Since it
is not the case anymore now, this patch is not needed at all.
Thanks.

Best Regards,
Pi-Cheng

>
> --
> viresh
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