linux-kernel - Re: [PATCH V4 07/14] cpufreq: mediatek: Add .get function

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Message-ID: <20220425100058.4kbvmpi63ygni6k5@vireshk-i7>
Date:   Mon, 25 Apr 2022 15:30:58 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Rex-BC Chen <rex-bc.chen@...iatek.com>
Cc:     rafael@...nel.org, robh+dt@...nel.org, krzk+dt@...nel.org,
        matthias.bgg@...il.com, jia-wei.chang@...iatek.com,
        roger.lu@...iatek.com, hsinyi@...gle.com, khilman@...libre.com,
        angelogioacchino.delregno@...labora.com, linux-pm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        Project_Global_Chrome_Upstream_Group@...iatek.com
Subject: Re: [PATCH V4 07/14] cpufreq: mediatek: Add .get function

On 25-04-22, 17:34, Rex-BC Chen wrote:
> We found that the pulses of cpu voltage could be observed when
> frequency is fixed (scaling_max_freq == scaling_min_freq) if using
> cpufreq_generic_get as '.get' callback in MT8186.
> cpufreq framework will constantly (~ 1 sec) call 'update' if the policy

Which function gets called here in that case ? I would expect
cpufreq_driver_target() to not make a call to MTK driver in that case, after it
finds that new and old frequency are same (it will check the corresponding freq
from cpufreq table).

> frequency is NOT equal to hardware frequency in
> cpufreq_verify_current_freq.
> The problem is that there might be a tiny difference between the policy
> frequency and the hardware frequency even they are very close.
> e.g. policy frequency is 500,000,000 Hz however, hardware frequency is
> 499,999,726 Hz for MT8186 opp15.
> 
> To prevent the voltage pulses, we currently use the software cached
> values as you pointed out.
> I wonder is it possible to add a tolerence for checking difference
> between policy frequency and hardware frequency in cpufreq framework so
> that we can use cpufreq_generic_get as callback without pulse issue.
> Or any suggestion would be appreciated.

-- 
viresh