usb: xhci-mtk: 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/host/xhci-mtk.c

@@ -212,6 +212,12 @@ static int xhci_mtk_clks_enable(struct xhci_hcd_mtk *mtk)
 {
 	int ret;
 
+	ret = clk_prepare_enable(mtk->ref_clk);
+	if (ret) {
+		dev_err(mtk->dev, "failed to enable ref_clk\n");
+		goto ref_clk_err;
+	}
+
 	ret = clk_prepare_enable(mtk->sys_clk);
 	if (ret) {
 		dev_err(mtk->dev, "failed to enable sys_clk\n");
@@ -238,6 +244,8 @@ static int xhci_mtk_clks_enable(struct xhci_hcd_mtk *mtk)
 usb_p0_err:
 	clk_disable_unprepare(mtk->sys_clk);
 sys_clk_err:
+	clk_disable_unprepare(mtk->ref_clk);
+ref_clk_err:
 	return -EINVAL;
 }
 
@@ -248,6 +256,7 @@ static void xhci_mtk_clks_disable(struct xhci_hcd_mtk *mtk)
 		clk_disable_unprepare(mtk->wk_deb_p0);
 	}
 	clk_disable_unprepare(mtk->sys_clk);
+	clk_disable_unprepare(mtk->ref_clk);
 }
 
 /* only clocks can be turn off for ip-sleep wakeup mode */
@@ -550,6 +559,12 @@ static int xhci_mtk_probe(struct platform_device *pdev)
 		return PTR_ERR(mtk->sys_clk);
 	}
 
+	mtk->ref_clk = devm_clk_get(dev, "ref_ck");
+	if (IS_ERR(mtk->ref_clk)) {
+		dev_err(dev, "fail to get ref_ck\n");
+		return PTR_ERR(mtk->ref_clk);
+	}
+
 	mtk->lpm_support = of_property_read_bool(node, "usb3-lpm-capable");
 
 	ret = usb_wakeup_of_property_parse(mtk, node);

drivers/usb/host/xhci-mtk.h

@@ -124,6 +124,7 @@ struct xhci_hcd_mtk {
 	struct regulator *vusb33;
 	struct regulator *vbus;
 	struct clk *sys_clk;	/* sys and mac clock */
+	struct clk *ref_clk;
 	struct clk *wk_deb_p0;	/* port0's wakeup debounce clock */
 	struct clk *wk_deb_p1;
 	struct regmap *pericfg;