linux-kernel - Re: [PATCH v7 0/4] qcom-cpufreq-hw: Add CPU clock provider support

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Message-ID: <20221117111207.GA93179@thinkpad>
Date:   Thu, 17 Nov 2022 16:42:07 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     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 v7 0/4] qcom-cpufreq-hw: Add CPU clock provider support

On Thu, Nov 17, 2022 at 10:19:03AM +0000, Sudeep Holla wrote:
> On Thu, Nov 17, 2022 at 11:01:41AM +0530, Manivannan Sadhasivam wrote:
> > Hello,
> > 
> > This series adds clock provider support to the Qcom CPUFreq driver for
> > supplying the clocks to the CPU cores in Qcom SoCs.
> > 
> > The Qualcomm platforms making use of CPUFreq HW Engine (EPSS/OSM) supply
> > clocks to the CPU cores. But this is not represented clearly in devicetree.
> > There is no clock coming out of the CPUFreq HW node to the CPU. This created
> > an issue [1] with the OPP core when a recent enhancement series was submitted.
> > Eventhough the issue got fixed in the OPP framework in the meantime, that's
> > not a proper solution and this series aims to fix it properly.
> > 
> > There was also an attempt made by Viresh [2] to fix the issue by moving the
> > clocks supplied to the CPUFreq HW node to the CPU. But that was not accepted
> > since those clocks belong to the CPUFreq HW node only.
> > 
> > The proposal here is to add clock provider support to the Qcom CPUFreq HW
> > driver to supply clocks to the CPUs that comes out of the EPSS/OSM block.
> > This correctly reflects the hardware implementation.
> > 
> > The clock provider is a simple one that just provides the frequency of the
> > clocks supplied to each frequency domain in the SoC using .recalc_rate()
> > callback. The frequency supplied by the driver will be 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.
> > 
> > This series has been tested on SM8450 based dev board with the OPP hack removed
> > and hence there is a DTS change only for that platform. Once this series gets
> > accepted, rest of the platform DTS can also be modified and finally the hack on
> > the OPP core can be dropped.
> > 
> > Thanks,
> > Mani
> > 
> > [1] https://lore.kernel.org/lkml/YsxSkswzsqgMOc0l@hovoldconsulting.com/
> > [2] https://lore.kernel.org/lkml/20220801054255.GA12039@thinkpad/t/
> > 
> > Changes in v7:
> > 
> > * Added a patch that returns the throttled frequency for cpufreq_driver->get()
> >   callback (Sudeep & Viresh)
> > * Added error check for kasprintf and allocated the clk name locally
> > 
> > Changes in v6:
> > 
> > * Removed the local variable clk_name (Matthias)
> > * Added the clock id to the error message of devm_clk_hw_register()
> > 
> > Changes in v5:
> > 
> > * Switched to Hz unit for the CPU clocks
> > 
> > Changes in v4:
> > 
> > * Rebased on top of cpufreq/arm/linux-next branch
> > 
> > Changes in v3:
> > 
> > * Submitted the cpufreq driver cleanup patches as a separate series as
> >   suggested by Viresh
> > * Removed static keyword from clk_init_data declaration
> > 
> > Changes in v2:
> > 
> > * Moved the qcom_cpufreq_data allocation to probe
> > * Added single clock provider with multiple clks for each freq domain
> > * Moved soc_data to qcom_cpufreq struct
> > * Added Rob's review for binding
> > 
> > Manivannan Sadhasivam (4):
> >   dt-bindings: cpufreq: cpufreq-qcom-hw: Add cpufreq clock provider
> >   arm64: dts: qcom: sm8450: Supply clock from cpufreq node to CPUs
> >   cpufreq: qcom-hw: Add CPU clock provider support
> 
> Why do you need the above 3 changes if the below(4/4) will ensure
> cpufreq_get(cpu) returns the clock frequency. I was expecting to drop the
> whole "confusing" clock bindings and the unnecessary clock provider.
> 
> Can't we just use cpufreq_get(cpu) ?
> 

This can be possible for OPP implementations for the CPUs but not for other
peripherals making use of OPP framework like GPU etc... Moreover this may end
up with different code path for CPUs and other peripherals inside OPP framework.

So I don't think it is applicable. But I'll defer it to Viresh.

Thanks,
Mani

> -- 
> Regards,
> Sudeep

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