clk: qcom: apss-ipq6018: ipq5332: add safe source switch for a53pll

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.

Additionally, not all SKUs of IPQ53xx support scaling. Hence,
do the above to the SKUs that support scaling.

Reviewed-by: Dmitry Baryshkov <[email protected]>
Signed-off-by: Kathiravan T <[email protected]>
Signed-off-by: Varadarajan Narayanan <[email protected]>
Link: https://lore.kernel.org/r/49422d258d67d33a2547fbb7f4f6e72d489c2301.1697781921.git.quic_varada@quicinc.com
Signed-off-by: Bjorn Andersson <[email protected]>

Author: quic-varada

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"
@@ -81,15 +84,68 @@ 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)
+{
+	struct clk_hw *hw;
+	u8 index;
+	int err;
+
+	if (action == PRE_RATE_CHANGE)
+		index = P_GPLL0;
+	else if (action == POST_RATE_CHANGE || action == ABORT_RATE_CHANGE)
+		index = P_APSS_PLL_EARLY;
+	else
+		return NOTIFY_OK;
+
+	hw = &apcs_alias0_clk_src.clkr.hw;
+	err = clk_rcg2_mux_closest_ops.set_parent(hw, index);
+
+	return notifier_from_errno(err);
+}
+
 static int apss_ipq6018_probe(struct platform_device *pdev)
 {
+	struct clk_hw *hw = &apcs_alias0_clk_src.clkr.hw;
+	struct notifier_block *cpu_clk_notifier;
 	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:
+		cpu_clk_notifier = devm_kzalloc(&pdev->dev,
+						sizeof(*cpu_clk_notifier),
+						GFP_KERNEL);
+		if (!cpu_clk_notifier)
+			return -ENOMEM;
+
+		cpu_clk_notifier->notifier_call = cpu_clk_notifier_fn;
+
+		ret = devm_clk_notifier_register(&pdev->dev, hw->clk, cpu_clk_notifier);
+		if (ret)
+			return ret;
+		break;
+	default:
+		break;
+	}
+
+	return 0;
 }
 
 static struct platform_driver apss_ipq6018_driver = {