linux-kernel - Re: [PATCH 2/2] cpufreq: don't call cpufreq_update

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Date:	Mon, 17 Feb 2014 14:24:43 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Pierre Ossman <pierre-list@...man.eu>
Subject: Re: [PATCH 2/2] cpufreq: don't call cpufreq_update_policy() on CPU addition

On 17 February 2014 14:13, Srivatsa S. Bhat
<srivatsa.bhat@...ux.vnet.ibm.com> wrote:
> On 02/14/2014 04:30 PM, Viresh Kumar wrote:
>> cpufreq_update_policy() is called from two places currently. From a workqueue
>> handled queued from cpufreq_bp_resume() for boot CPU and from
>> cpufreq_cpu_callback() whenever a CPU is added.
>>
>> The first one makes sure that boot CPU is running on the frequency present in
>> policy->cpu. But we don't really need a call from cpufreq_cpu_callback(),
>> because we always call cpufreq_driver->init() (which will set policy->cur
>> correctly) whenever first CPU of any policy is added back. And so every policy
>> structure is guaranteed to have the right frequency in policy->cur.
>>
>
> This wording is slightly inaccurate. ->init() may or may not set policy->cur
> (for example, powernowk8 driver doesn't set it in the init routine)..

Its not the wording that is wrong but this particular driver then :)
This is what Documentation/cpu-drivers.txt says:

1.2 Per-CPU Initialization
Then, the driver must fill in the following values:

policy->cur The current operating frequency of
this CPU (if appropriate)

And so it is supposed to do it.

> But we set it for sure in __cpufreq_add_dev():
>
> 1117         if (cpufreq_driver->get) {
> 1118                 policy->cur = cpufreq_driver->get(policy->cpu);
> 1119                 if (!policy->cur) {
> 1120                         pr_err("%s: ->get() failed\n", __func__);
> 1121                         goto err_get_freq;
> 1122                 }
> 1123         }

Its just about removing that from drivers and doing it once in core :)

>> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
>
> The reasoning and the code looks good to me.
>
> Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>

Thanks.
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