USB: dwc3-msm: Add support for setting specific frequency for core clock

Add support for setting USB core clock to particular frequency so that
core clock frequency can be passed through dts property.

Change-Id: If9ff41037d22d7be7f09c9468e8d4cc92280a28e
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>

Documentation/devicetree/bindings/usb/msm-ssusb.txt

@@ -50,6 +50,7 @@ Optional properties :
 - qcom,disable-dev-mode-pm: If present, it disables PM runtime functionality for device mode.
 - qcom,disable-host-mode-pm: If present, it disables XHCI PM runtime functionality when USB
   host mode is used.
+- qcom,core-clk-rate: If present, indicates clock frequency to be set for USB master clock.
 - extcon: phandles to external connector devices. First phandle should point to
 	  external connector, which provide "USB" cable events, the second
 	  should point to external connector device, which provide "USB-HOST"

drivers/usb/dwc3/dwc3-msm.c

@@ -2338,14 +2338,23 @@ static int dwc3_msm_get_clk_gdsc(struct dwc3_msm *mdwc)
 		return ret;
 	}
 
-	/*
-	 * Get Max supported clk frequency for USB Core CLK and request
-	 * to set the same.
-	 */
-	mdwc->core_clk_rate = clk_round_rate(mdwc->core_clk, LONG_MAX);
+	if (!of_property_read_u32(mdwc->dev->of_node, "qcom,core-clk-rate",
+				(u32 *)&mdwc->core_clk_rate)) {
+		mdwc->core_clk_rate = clk_round_rate(mdwc->core_clk,
+							mdwc->core_clk_rate);
+	} else {
+		/*
+		 * Get Max supported clk frequency for USB Core CLK and request
+		 * to set the same.
+		 */
+		mdwc->core_clk_rate = clk_round_rate(mdwc->core_clk, LONG_MAX);
+	}
+
 	if (IS_ERR_VALUE(mdwc->core_clk_rate)) {
 		dev_err(mdwc->dev, "fail to get core clk max freq.\n");
 	} else {
+		dev_dbg(mdwc->dev, "USB core frequency = %ld\n",
+							mdwc->core_clk_rate);
 		ret = clk_set_rate(mdwc->core_clk, mdwc->core_clk_rate);
 		if (ret)
 			dev_err(mdwc->dev, "fail to set core_clk freq:%d\n",