usb: dwc3: core: introduce dwc3_core_is_valid()

This little helper will be used to make sure we're
dealing with a valid Synopsys DWC3 or DWC3.1 core.
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/dwc3/core.c

@@ -594,19 +594,12 @@ static void dwc3_core_exit(struct dwc3 *dwc)
 	phy_power_off(dwc->usb3_generic_phy);
 }
 
-/**
- * dwc3_core_init - Low-level initialization of DWC3 Core
- * @dwc: Pointer to our controller context structure
- *
- * Returns 0 on success otherwise negative errno.
- */
-static int dwc3_core_init(struct dwc3 *dwc)
+static bool dwc3_core_is_valid(struct dwc3 *dwc)
 {
-	u32			hwparams4 = dwc->hwparams.hwparams4;
-	u32			reg;
-	int			ret;
+	u32 reg;
 
 	reg = dwc3_readl(dwc->regs, DWC3_GSNPSID);
+
 	/* This should read as U3 followed by revision number */
 	if ((reg & DWC3_GSNPSID_MASK) == 0x55330000) {
 		/* Detected DWC_usb3 IP */
@@ -616,6 +609,25 @@ static int dwc3_core_init(struct dwc3 *dwc)
 		dwc->revision = dwc3_readl(dwc->regs, DWC3_VER_NUMBER);
 		dwc->revision |= DWC3_REVISION_IS_DWC31;
 	} else {
+		return false;
+	}
+
+	return true;
+}
+
+/**
+ * dwc3_core_init - Low-level initialization of DWC3 Core
+ * @dwc: Pointer to our controller context structure
+ *
+ * Returns 0 on success otherwise negative errno.
+ */
+static int dwc3_core_init(struct dwc3 *dwc)
+{
+	u32			hwparams4 = dwc->hwparams.hwparams4;
+	u32			reg;
+	int			ret;
+
+	if (!dwc3_core_is_valid(dwc)) {
 		dev_err(dwc->dev, "this is not a DesignWare USB3 DRD Core\n");
 		ret = -ENODEV;
 		goto err0;