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

From: Viresh Kumar <viresh.kumar@linaro.org>
To: Rex-BC Chen <rex-bc.chen@mediatek.com>
Cc: rafael@kernel.org, robh+dt@kernel.org, krzk+dt@kernel.org,
	matthias.bgg@gmail.com, jia-wei.chang@mediatek.com,
	roger.lu@mediatek.com, hsinyi@google.com, khilman@baylibre.com,
	angelogioacchino.delregno@collabora.com,
	linux-pm@vger.kernel.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-mediatek@lists.infradead.org,
	Project_Global_Chrome_Upstream_Group@mediatek.com
Subject: Re: [PATCH V4 07/14] cpufreq: mediatek: Add .get function
Date: Wed, 27 Apr 2022 08:41:41 +0530	[thread overview]
Message-ID: <20220427031141.or2owu5wrh2cadfo@vireshk-i7> (raw)
In-Reply-To: <078b1f9b39690da98cbd3c4528ba28374a097083.camel@mediatek.com>

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