+static int phy_power_on(struct stm32_dwmac *bsp_priv, bool enable)

I find this function name confusing, since 50% of the time it does not
actually power the PHY on. You never call it with anything other than
a static true/false value. So it might was well be two functions,
phy_power_on() and phy_power_off().

+{
+	int ret;
+	struct device *dev = bsp_priv->dev;
+
+	if (!bsp_priv->regulator)
+		return 0;
+
+	if (enable) {
+		ret = regulator_enable(bsp_priv->regulator);
+		if (ret)
+			dev_err(dev, "fail to enable phy-supply\n");

Not all PHYs are usable in 0 picoseconds. You probably want a delay
here. Otherwise the first few accesses to it might not work.

      Andrew