linux-kernel - Re: [PATCH v1 04/10] clk: qcom: apss-ipq6018: ipq5332: add safe source switch for a53pll

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Message-ID: <20230929073216.GB15001@varda-linux.qualcomm.com>
Date:   Fri, 29 Sep 2023 13:02:17 +0530
From:   Varadarajan Narayanan <quic_varada@...cinc.com>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>
CC:     <ilia.lin@...nel.org>, <agross@...nel.org>, <andersson@...nel.org>,
        <rafael@...nel.org>, <viresh.kumar@...aro.org>,
        <robh+dt@...nel.org>, <krzysztof.kozlowski+dt@...aro.org>,
        <conor+dt@...nel.org>, <mturquette@...libre.com>,
        <sboyd@...nel.org>, <quic_kathirav@...cinc.com>,
        <linux-pm@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-clk@...r.kernel.org>
Subject: Re: [PATCH v1 04/10] clk: qcom: apss-ipq6018: ipq5332: add safe
 source switch for a53pll

On Thu, Sep 07, 2023 at 10:31:55AM +0200, Konrad Dybcio wrote:
> On 7.09.2023 07:21, Varadarajan Narayanan wrote:
> > Stromer Plus PLL found on IPQ53xx doesn't support dynamic
> > frequency scaling. To achieve the same, we need to park the APPS
> > PLL source to GPLL0, re configure the PLL and then switch the
> > source to APSS_PLL_EARLY.
> >
> > To support this, register a clock notifier to get the PRE_RATE
> > and POST_RATE notification. Change the APSS PLL source to GPLL0
> > when PRE_RATE notification is received, then configure the PLL
> > and then change back the source to APSS_PLL_EARLY.
> >
> > Signed-off-by: Kathiravan T <quic_kathirav@...cinc.com>
> > Signed-off-by: Varadarajan Narayanan <quic_varada@...cinc.com>
> > ---
> >  drivers/clk/qcom/apss-ipq6018.c | 54 ++++++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 53 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/clk/qcom/apss-ipq6018.c b/drivers/clk/qcom/apss-ipq6018.c
> > index 4e13a08..ffb6ab5 100644
> > --- a/drivers/clk/qcom/apss-ipq6018.c
> > +++ b/drivers/clk/qcom/apss-ipq6018.c
> > @@ -9,8 +9,11 @@
> >  #include <linux/clk-provider.h>
> >  #include <linux/regmap.h>
> >  #include <linux/module.h>
> > +#include <linux/clk.h>
> > +#include <linux/soc/qcom/smem.h>
> >
> >  #include <dt-bindings/clock/qcom,apss-ipq.h>
> > +#include <dt-bindings/arm/qcom,ids.h>
> >
> >  #include "common.h"
> >  #include "clk-regmap.h"
> > @@ -84,15 +87,64 @@ static const struct qcom_cc_desc apss_ipq6018_desc = {
> >  	.num_clks = ARRAY_SIZE(apss_ipq6018_clks),
> >  };
> >
> > +static int cpu_clk_notifier_fn(struct notifier_block *nb, unsigned long action,
> > +				void *data)
> > +{
> > +	u8 index;
> > +	int err;
> > +
> > +	if (action == PRE_RATE_CHANGE)
> > +		index = P_GPLL0;
> > +	else if (action == POST_RATE_CHANGE)
> > +		index = P_APSS_PLL_EARLY;
> > +	else
> > +		return 0;
> > +
> > +	err = clk_rcg2_mux_closest_ops.set_parent(&apcs_alias0_clk_src.clkr.hw,
> > +						  index);
> Adding a variable for clk_hw within the apcs_alias0 clock would
> make this easier to digest, I think.
>
> And if we wanna be even less error-prone, you can reference the
> ops of this clock in an indirect way.

Will change it as

	struct clk_hw *hw;

	hw = &apcs_alias0_clk_src.clkr.hw;
	err = hw->init->ops->set_parent(hw, index);

> > +	return notifier_from_errno(err);
> > +}
> > +
> > +static struct notifier_block cpu_clk_notifier = {
> > +	.notifier_call = cpu_clk_notifier_fn,
> > +};
> > +
> >  static int apss_ipq6018_probe(struct platform_device *pdev)
> >  {
> >  	struct regmap *regmap;
> > +	u32 soc_id;
> > +	int ret;
> > +
> > +	ret = qcom_smem_get_soc_id(&soc_id);
> > +	if (ret)
> > +		return ret;
> >
> >  	regmap = dev_get_regmap(pdev->dev.parent, NULL);
> >  	if (!regmap)
> >  		return -ENODEV;
> >
> > -	return qcom_cc_really_probe(pdev, &apss_ipq6018_desc, regmap);
> > +	ret = qcom_cc_really_probe(pdev, &apss_ipq6018_desc, regmap);
> > +	if (ret)
> > +		return ret;
> > +
> > +	switch (soc_id) {
> > +	/*
> > +	 * Only below variants of IPQ53xx support scaling
> > +	 */
> 1. /* Keep this in a 1-line comment */

Ok

> 2. why? explain the reasoning in the commit message

Ok

Thanks
Varada

> > +	case QCOM_ID_IPQ5332:
> > +	case QCOM_ID_IPQ5322:
> > +	case QCOM_ID_IPQ5300:
> > +		ret = clk_notifier_register(apcs_alias0_clk_src.clkr.hw.clk,
> > +						&cpu_clk_notifier);
> > +		if (ret)
> > +			return ret;
> > +		break;
> > +	default:
> > +		break;
> > +	}
> > +
> > +	return 0;
> >  }
> >
> >  static struct platform_driver apss_ipq6018_driver = {