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

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Date:   Fri, 21 Oct 2022 13:32:41 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     andersson@...nel.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 0/4] qcom-cpufreq-hw: Add CPU clock provider support

On Thu, Oct 20, 2022 at 10:52:30AM +0530, Viresh Kumar wrote:
> + Johan,
> 
> On 19-10-22, 19:29, 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 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 for working on this Mani.
> 
> Can you also test the below code over your series ? This shouldn't
> result in issues that Johan reported earlier [1][2]. Below is the hack I
> am carrying in the OPP core for Qcom SoCs at the moment.
> 
> diff --git a/drivers/opp/core.c b/drivers/opp/core.c
> index e87567dbe99f..b7158d33c13d 100644
> --- a/drivers/opp/core.c
> +++ b/drivers/opp/core.c
> @@ -1384,20 +1384,6 @@ static struct opp_table *_update_opp_table_clk(struct device *dev,
>         }
> 
>         if (ret == -ENOENT) {
> -               /*
> -                * There are few platforms which don't want the OPP core to
> -                * manage device's clock settings. In such cases neither the
> -                * platform provides the clks explicitly to us, nor the DT
> -                * contains a valid clk entry. The OPP nodes in DT may still
> -                * contain "opp-hz" property though, which we need to parse and
> -                * allow the platform to find an OPP based on freq later on.
> -                *
> -                * This is a simple solution to take care of such corner cases,
> -                * i.e. make the clk_count 1, which lets us allocate space for
> -                * frequency in opp->rates and also parse the entries in DT.
> -                */
> -               opp_table->clk_count = 1;
> -
>                 dev_dbg(dev, "%s: Couldn't find clock: %d\n", __func__, ret);
>                 return opp_table;
>         }
> diff --git a/drivers/opp/debugfs.c b/drivers/opp/debugfs.c
> index 96a30a032c5f..402c507edac7 100644
> --- a/drivers/opp/debugfs.c
> +++ b/drivers/opp/debugfs.c
> @@ -138,7 +138,7 @@ void opp_debug_create_one(struct dev_pm_opp *opp, struct opp_table *opp_table)
>          * - For some devices rate isn't available or there are multiple, use
>          *   index instead for them.
>          */
> -       if (likely(opp_table->clk_count == 1 && opp->rates[0]))
> +       if (likely(opp_table->clk_count == 1))
>                 id = opp->rates[0];
>         else
>                 id = _get_opp_count(opp_table);
> 

With the above diffs applied, I no longer see the issues reported by Johan on
SM8450 dev board.

Thanks,
Mani

> -- 
> viresh
> 
> [1] https://lore.kernel.org/all/YsxSkswzsqgMOc0l@hovoldconsulting.com/
> [2] https://lore.kernel.org/all/Ys2FZa6YDwt7d%2FZc@hovoldconsulting.com/

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