linux-kernel - Re: [PATCH v5 3/3] cpufreq: qcom-hw: Add CPU clock provider support

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Message-ID: <20221109074908.GC4651@thinkpad>
Date:   Wed, 9 Nov 2022 13:19:08 +0530
From:   Manivannan Sadhasivam <mani@...nel.org>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        andersson@...nel.org, viresh.kumar@...aro.org,
        krzysztof.kozlowski+dt@...aro.org, rafael@...nel.org,
        robh+dt@...nel.org, johan@...nel.org, devicetree@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH v5 3/3] cpufreq: qcom-hw: Add CPU clock provider support

On Tue, Nov 08, 2022 at 03:57:17PM +0000, Sudeep Holla wrote:
> On Tue, Nov 08, 2022 at 09:10:37PM +0530, Manivannan Sadhasivam wrote:
> > Qcom CPUFreq hardware (EPSS/OSM) controls clock and voltage to the CPU
> > cores. But this relationship is not represented with the clk framework
> > so far.
> > 
> > So, let's make the qcom-cpufreq-hw driver a clock provider. This makes the
> > clock producer/consumer relationship cleaner and is also useful for CPU
> > related frameworks like OPP to know the frequency at which the CPUs are
> > running.
> > 
> > The clock frequency provided by the driver is for each frequency domain.
> > We cannot get the frequency of each CPU core because, not all platforms
> > support per-core DCVS feature.
> > 
> > Also the frequency supplied by the driver is the actual frequency that
> > comes out of the EPSS/OSM block after the DCVS operation. This frequency is
> > not same as what the CPUFreq framework has set but it is the one that gets
> > supplied to the CPUs after throttling by LMh.
> >
> 
> OK now I see more info here. How different is this value from the one
> returned by qcom_cpufreq_hw_get() ?
> 

qcom_cpufreq_hw_get() returns the frequency that got programmed by the cpufreq
core. But that frequency is not necessarily the one that gets delivered to the
CPU cores because the EPSS/OSM hardware block may vary the frequency after the
DCVS operation.

So this frequency is the final one that gets delivered to the CPU cores.

Thanks,
Mani

> -- 
> Regards,
> Sudeep

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