linux-kernel - Re: [PATCH v7 3/8] cpufreq: kirkwood: Remove use of the clk provider API

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Date:	Fri, 22 Aug 2014 22:27:18 +0200
From:	Andrew Lunn <andrew@...n.ch>
To:	Andrew Lunn <andrew@...n.ch>
Cc:	Mike Turquette <mturquette@...aro.org>,
	Tomeu Vizoso <tomeu.vizoso@...labora.com>,
	Stephen Warren <swarren@...dotorg.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Peter De Schrijver <pdeschrijver@...dia.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	linux-kernel@...r.kernel.org, Rabin Vincent <rabin@....in>,
	Tomasz Figa <t.figa@...sung.com>,
	Thierry Reding <thierry.reding@...il.com>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v7 3/8] cpufreq: kirkwood: Remove use of the clk provider
 API

> It was clearer in earlier versions of the driver, but code has been
> refactored into the cpufreq core. The core should call
> kirkwood_cpufreq_get_cpu_frequency() in order to get the current
> frequency, and only perform a change if the requested frequency is
> different. In the current code, kirkwood_cpufreq_get_cpu_frequency()
> reads from the hardware what the current frequency is. So we are
> guaranteed to only call kirkwood_cpufreq_target() when there is a real
> change.

Hi Mike

I went looking at the core.

drivers/cpufreq/cpufreq.c:__cpufreq_add_dev() contains:

        if (cpufreq_driver->get && !cpufreq_driver->setpolicy) {
                policy->cur = cpufreq_driver->get(policy->cpu);
                if (!policy->cur) {
                        pr_err("%s: ->get() failed\n", __func__);
                        goto err_get_freq;
                }
        }

So this gets the current frequency from the driver, when the driver is
added. So for the current code, this gets the real state of the
hardware.

and

drivers/cpufreq/cpufreq.c:__cpufreq_driver_target() contains:

        /*
         * This might look like a redundant call as we are checking it again
         * after finding index. But it is left intentionally for cases where
         * exactly same freq is called again and so we can save on few function
         * calls.
         */
        if (target_freq == policy->cur)
                return 0;

        /* Save last value to restore later on errors */
        policy->restore_freq = policy->cur;

        if (cpufreq_driver->target)
                retval = cpufreq_driver->target(policy, target_freq, relation);

and here it will only call the function to change the frequency, if it
is different from the current frequency.

   Andrew
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