clk: sunxi-ng: h6: Reparent CPUX during PLL CPUX rate change

While PLL CPUX clock rate change when CPU is running from it works in
vast majority of cases, now and then it causes instability. This leads
to system crashes and other undefined behaviour. After a lot of testing
(30+ hours) while also doing a lot of frequency switches, we can't
observe any instability issues anymore when doing reparenting to stable
clock like 24 MHz oscillator.

Fixes: 524353e ("clk: sunxi-ng: add support for the Allwinner H6 CCU")
Reported-by: Chad Wagner <wagnerch42@gmail.com>
Link: https://forum.libreelec.tv/thread/27295-orange-pi-3-lts-freezes/
Tested-by: Chad Wagner <wagnerch42@gmail.com>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Link: https://lore.kernel.org/r/20231013181712.2128037-1-jernej.skrabec@gmail.com
Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>

drivers/clk/sunxi-ng/ccu-sun50i-h6.c

@@ -1181,11 +1181,18 @@ static const u32 usb2_clk_regs[] = {
 	SUN50I_H6_USB3_CLK_REG,
 };
 
+static struct ccu_mux_nb sun50i_h6_cpu_nb = {
+	.common		= &cpux_clk.common,
+	.cm		= &cpux_clk.mux,
+	.delay_us       = 1,
+	.bypass_index   = 0, /* index of 24 MHz oscillator */
+};
+
 static int sun50i_h6_ccu_probe(struct platform_device *pdev)
 {
 	void __iomem *reg;
+	int i, ret;
 	u32 val;
-	int i;
 
 	reg = devm_platform_ioremap_resource(pdev, 0);
 	if (IS_ERR(reg))
@@ -1252,7 +1259,15 @@ static int sun50i_h6_ccu_probe(struct platform_device *pdev)
 	val |= BIT(24);
 	writel(val, reg + SUN50I_H6_HDMI_CEC_CLK_REG);
 
-	return devm_sunxi_ccu_probe(&pdev->dev, reg, &sun50i_h6_ccu_desc);
+	ret = devm_sunxi_ccu_probe(&pdev->dev, reg, &sun50i_h6_ccu_desc);
+	if (ret)
+		return ret;
+
+	/* Reparent CPU during PLL CPUX rate changes */
+	ccu_mux_notifier_register(pll_cpux_clk.common.hw.clk,
+				  &sun50i_h6_cpu_nb);
+
+	return 0;
 }
 
 static const struct of_device_id sun50i_h6_ccu_ids[] = {