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

[Varadarajan Narayanan <quic_varada@quicinc.com>]

On Thu, Sep 07, 2023 at 04:54:56PM +0300, Dmitry Baryshkov wrote:
> On Thu, 7 Sept 2023 at 08:22, Varadarajan Narayanan
> <quic_varada@quicinc.com> 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.
>
> This means that we are changing the parents behind the back of CCF,
> which is not great.

Unfortunately, we are not aware of any other way to do this.
Please let me know if there is a better way to do this, will
implement that and post a revision.

> > Signed-off-by: Kathiravan T <quic_kathirav@quicinc.com>
> > Signed-off-by: Varadarajan Narayanan <quic_varada@quicinc.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;
>
> I don't see P_GPLL0 being supported in the ipq6018 driver.

This comes from one of the dependency patches mentioned in the
cover letter [https://lore.kernel.org/linux-arm-msm/20230904-gpll_cleanup-v1-0-de2c448f1188@quicinc.com/].
Please refer to patch https://lore.kernel.org/linux-arm-msm/20230904-gpll_cleanup-v1-6-de2c448f1188@quicinc.com/.

>
> > +       else if (action == POST_RATE_CHANGE)
> > +               index = P_APSS_PLL_EARLY;
>
> You also have to handle ABORT_RATE_CHANGE here.

ok.

> > +       else
> > +               return 0;
> > +
> > +       err = clk_rcg2_mux_closest_ops.set_parent(&apcs_alias0_clk_src.clkr.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
> > +        */
> > +       case QCOM_ID_IPQ5332:
> > +       case QCOM_ID_IPQ5322:
> > +       case QCOM_ID_IPQ5300:
>
> Please use compat strings instead of using the soc-id.

We have a common compatible string for all IPQ53xx CPUs across
boards.  The CPU variant is identified from fuse settings. Not
sure how we can differentiate between the variants using compat
strings. Can you kindly help.

Thanks
varada

> > +               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 = {
> > --
> > 2.7.4
> >
>
>
> --
> With best wishes
>
> Dmitry