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

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Date:	Fri, 22 Jul 2016 23:31:06 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Andreas Herrmann <aherrmann@...e.com>,
	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 Friday, July 22, 2016 08:36:56 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.

Why would it fail?  If governor->max_transition_latency is non-zero, but less
than UNIT_MAX, the condition checked will be true to my eyes.

Thanks,
Rafael