Date:   Thu, 20 Oct 2022 10:52:30 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...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

+ 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);

-- 
viresh

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

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