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

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Date:   Wed, 27 Apr 2022 08:41:41 +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 26-04-22, 19:13, Rex-BC Chen wrote:
> We have a non-upstream driver which tries to get frequency by
> 'cpufreq_get'.

This is the right thing to do there.

> When we use that non-upstream driver, 'cpufreq_verify_current_freq'
> will be further invoked by 'cpufreq_get' and it would cause voltage
> pulse issue as I described previously.

I see this will eventually resolve to __cpufreq_driver_target(), which
should return without any frequency updates.

What do you mean by "voltage pulse" here? What actually happens which
you want to avoid.

> Therefore, we apply the solution in this series.

I won't call it a solution but a Bug as .get() is supposed to read
real freq of the hardware.

> Recently, we found that using 'cpufreq_generic_get' directly in our
> non-upstream driver can do the same thing without pulse issue.

That would be an abuse of the cpufreq_generic_get() API. It is ONLY
allowed to be used while setting .get callback in the driver.

-- 
viresh