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

[Konrad Dybcio <konrad.dybcio@linaro.org>]

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@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;
> +	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.

> +
> +	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 */

2. why? explain the reasoning in the commit message

Konrad
> +	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 = {