phy: stm32: ensure pll is disabled before phys creation

To ensure a good balancing of regulators, force PLL disable either by
reset or by clearing the PLLEN bit.
If waiting the powerdown pulse delay isn't enough, return -EPROBE_DEFER
instead of polling the PLLEN bit, which will be low at the next probe.

Signed-off-by: Amelie Delaunay <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Vinod Koul <[e-mail]>

drivers/phy/st/phy-stm32-usbphyc.c

···
 #include <linux/bitfield.h>
 #include <linux/clk.h>
 #include <linux/delay.h>
-#include <linux/io.h>
+#include <linux/iopoll.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/of_platform.h>
···
 	struct device *dev = &pdev->dev;
 	struct device_node *child, *np = dev->of_node;
 	struct phy_provider *phy_provider;
-	u32 version;
+	u32 pllen, version;
 	int ret, port = 0;
 
 	usbphyc = devm_kzalloc(dev, sizeof(*usbphyc), GFP_KERNEL);
···
 		ret = PTR_ERR(usbphyc->rst);
 		if (ret == -EPROBE_DEFER)
 			goto clk_disable;
+
+		stm32_usbphyc_clr_bits(usbphyc->base + STM32_USBPHYC_PLL, PLLEN);
+	}
+
+	/*
+	 * Wait for minimum width of powerdown pulse (ENABLE = Low):
+	 * we have to ensure the PLL is disabled before phys initialization.
+	 */
+	if (readl_relaxed_poll_timeout(usbphyc->base + STM32_USBPHYC_PLL,
+				       pllen, !(pllen & PLLEN), 5, 50)) {
+		dev_warn(usbphyc->dev, "PLL not reset\n");
+		ret = -EPROBE_DEFER;
+		goto clk_disable;
 	}
 
 	usbphyc->switch_setup = -EINVAL;