usb: mtu3: add reference clock

usually, the reference clock comes from 26M oscillator directly,
but some SoCs are not, add it for compatibility.
Signed-off-by: NChunfeng Yun <chunfeng.yun@mediatek.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/mtu3/mtu3.h

@@ -225,6 +225,7 @@ struct ssusb_mtk {
 	/* common power & clock */
 	struct regulator *vusb33;
 	struct clk *sys_clk;
+	struct clk *ref_clk;
 	/* otg */
 	struct otg_switch_mtk otg_switch;
 	enum usb_dr_mode dr_mode;

drivers/usb/mtu3/mtu3_plat.c

@@ -123,7 +123,13 @@ static int ssusb_rscs_init(struct ssusb_mtk *ssusb)
 	ret = clk_prepare_enable(ssusb->sys_clk);
 	if (ret) {
 		dev_err(ssusb->dev, "failed to enable sys_clk\n");
-		goto clk_err;
+		goto sys_clk_err;
+	}
+
+	ret = clk_prepare_enable(ssusb->ref_clk);
+	if (ret) {
+		dev_err(ssusb->dev, "failed to enable ref_clk\n");
+		goto ref_clk_err;
 	}
 
 	ret = ssusb_phy_init(ssusb);
@@ -143,8 +149,10 @@ static int ssusb_rscs_init(struct ssusb_mtk *ssusb)
 phy_err:
 	ssusb_phy_exit(ssusb);
 phy_init_err:
+	clk_disable_unprepare(ssusb->ref_clk);
+ref_clk_err:
 	clk_disable_unprepare(ssusb->sys_clk);
-clk_err:
+sys_clk_err:
 	regulator_disable(ssusb->vusb33);
 vusb33_err:
 
@@ -154,6 +162,7 @@ static int ssusb_rscs_init(struct ssusb_mtk *ssusb)
 static void ssusb_rscs_exit(struct ssusb_mtk *ssusb)
 {
 	clk_disable_unprepare(ssusb->sys_clk);
+	clk_disable_unprepare(ssusb->ref_clk);
 	regulator_disable(ssusb->vusb33);
 	ssusb_phy_power_off(ssusb);
 	ssusb_phy_exit(ssusb);
@@ -216,6 +225,12 @@ static int get_ssusb_rscs(struct platform_device *pdev, struct ssusb_mtk *ssusb)
 		return PTR_ERR(ssusb->sys_clk);
 	}
 
+	ssusb->ref_clk = devm_clk_get(dev, "ref_ck");
+	if (IS_ERR(ssusb->ref_clk)) {
+		dev_err(dev, "failed to get ref clock\n");
+		return PTR_ERR(ssusb->ref_clk);
+	}
+
 	ssusb->num_phys = of_count_phandle_with_args(node,
 			"phys", "#phy-cells");
 	if (ssusb->num_phys > 0) {
@@ -428,6 +443,7 @@ static int __maybe_unused mtu3_suspend(struct device *dev)
 	ssusb_host_disable(ssusb, true);
 	ssusb_phy_power_off(ssusb);
 	clk_disable_unprepare(ssusb->sys_clk);
+	clk_disable_unprepare(ssusb->ref_clk);
 	ssusb_wakeup_enable(ssusb);
 
 	return 0;
@@ -445,6 +461,7 @@ static int __maybe_unused mtu3_resume(struct device *dev)
 
 	ssusb_wakeup_disable(ssusb);
 	clk_prepare_enable(ssusb->sys_clk);
+	clk_prepare_enable(ssusb->ref_clk);
 	ssusb_phy_power_on(ssusb);
 	ssusb_host_enable(ssusb);