linux-kernel - Re: [PATCH] Revert "cpufreq: pcc-cpufreq: update default value of cpuinfo_transition

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Date:	Fri, 22 Jul 2016 15:25:43 -0400
From:	Linda Knippers <linda.knippers@....com>
To:	Viresh Kumar <viresh.kumar@...aro.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Andreas Herrmann <aherrmann@...e.com>
CC:	Jacob Tanenbaum <jtanenba@...hat.com>, <stable@...r.kernel.org>,
	<linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Revert "cpufreq: pcc-cpufreq: update default value of
 cpuinfo_transition_latency"



On 7/22/2016 11:36 AM, Viresh Kumar wrote:
> On 22-07-16, 17:14, Andreas Herrmann wrote:
>> diff --git a/drivers/cpufreq/pcc-cpufreq.c b/drivers/cpufreq/pcc-cpufreq.c
>> index a7ecb9a..3f0ce2a 100644
>> --- a/drivers/cpufreq/pcc-cpufreq.c
>> +++ b/drivers/cpufreq/pcc-cpufreq.c
>> @@ -555,8 +555,6 @@ static int pcc_cpufreq_cpu_init(struct cpufreq_policy *policy)
>>  	policy->min = policy->cpuinfo.min_freq =
>>  		ioread32(&pcch_hdr->minimum_frequency) * 1000;
>>  
>> -	policy->cpuinfo.transition_latency = CPUFREQ_ETERNAL;
>> -
>>  	pr_debug("init: policy->max is %d, policy->min is %d\n",
>>  		policy->max, policy->min);
>>  out:
> 
> Hi Rafael,
> 
> I am very confused on this, can you help me understand ?
> 
> - CPUFREQ_ETERNAL = -1
> - unsigned int transition_latency = CPUFREQ_ETERNAL, will set it to UINT_MAX.
> - Many drivers do it today
> 
> cpufreq.c
> 
> 	if (policy->governor->max_transition_latency &&
> 	    policy->cpuinfo.transition_latency >
> 	    policy->governor->max_transition_latency) {
> 
> - And this check will always fail, unless max_transition_latency is zero.
> 
> What am I missing ?

I don't know what's missing but I can reproduce the problem.

-- ljk