usb: dwc3: Calculate REFCLKPER based on reference clock

Instead of using a special property to determine the reference clock
period, use the rate of the reference clock. When we have a legacy
snps,ref-clock-period-ns property and no reference clock, use it
instead. Fractional clocks are not currently supported, and will be
dealt with in the next commit.
Tested-by: Robert Hancock <robert.hancock@calian.com>
Reviewed-by: Robert Hancock <robert.hancock@calian.com>
Reviewed-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Link: https://lore.kernel.org/r/20220127200636.1456175-4-sean.anderson@seco.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/dwc3/core.c

@@ -347,14 +347,24 @@ static void dwc3_frame_length_adjustment(struct dwc3 *dwc)
  */
 static void dwc3_ref_clk_period(struct dwc3 *dwc)
 {
+	unsigned long period;
+	unsigned long rate;
 	u32 reg;
 
-	if (dwc->ref_clk_per == 0)
+	if (dwc->ref_clk) {
+		rate = clk_get_rate(dwc->ref_clk);
+		if (!rate)
 			return;
+		period = NSEC_PER_SEC / rate;
+	} else if (dwc->ref_clk_per) {
+		period = dwc->ref_clk_per;
+	} else {
+		return;
+	}
 
 	reg = dwc3_readl(dwc->regs, DWC3_GUCTL);
 	reg &= ~DWC3_GUCTL_REFCLKPER_MASK;
-	reg |=  FIELD_PREP(DWC3_GUCTL_REFCLKPER_MASK, dwc->ref_clk_per);
+	reg |=  FIELD_PREP(DWC3_GUCTL_REFCLKPER_MASK, period);
 	dwc3_writel(dwc->regs, DWC3_GUCTL, reg);
 }