phy: fsl-imx8mq-usb: support alternate reference clock

This phy supports both 24MHz and 100MHz clock inputs. By default it's
using XTAL 24MHz and the 100MHz clock is a alternate reference clock.
Add supports to use alternate reference clock in case 24MHz clock
can't work well.

Reviewed-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Xu Yang <xu.yang_2@nxp.com>
Link: https://patch.msgid.link/20251118071947.2504789-2-xu.yang_2@nxp.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

Author: Xu Yang

drivers/phy/freescale/phy-fsl-imx8mq-usb.c

@@ -16,6 +16,7 @@
 #define PHY_CTRL0_REF_SSP_EN		BIT(2)
 #define PHY_CTRL0_FSEL_MASK		GENMASK(10, 5)
 #define PHY_CTRL0_FSEL_24M		0x2a
+#define PHY_CTRL0_FSEL_100M		0x27
 
 #define PHY_CTRL1			0x4
 #define PHY_CTRL1_RESET			BIT(0)
@@ -108,6 +109,7 @@ struct tca_blk {
 struct imx8mq_usb_phy {
 	struct phy *phy;
 	struct clk *clk;
+	struct clk *alt_clk;
 	void __iomem *base;
 	struct regulator *vbus;
 	struct tca_blk *tca;
@@ -582,7 +584,8 @@ static int imx8mp_usb_phy_init(struct phy *phy)
 	/* USB3.0 PHY signal fsel for 24M ref */
 	value = readl(imx_phy->base + PHY_CTRL0);
 	value &= ~PHY_CTRL0_FSEL_MASK;
-	value |= FIELD_PREP(PHY_CTRL0_FSEL_MASK, PHY_CTRL0_FSEL_24M);
+	value |= FIELD_PREP(PHY_CTRL0_FSEL_MASK, imx_phy->alt_clk ?
+			    PHY_CTRL0_FSEL_100M : PHY_CTRL0_FSEL_24M);
 	writel(value, imx_phy->base + PHY_CTRL0);
 
 	/* Disable alt_clk_en and use internal MPLL clocks */
@@ -626,13 +629,24 @@ static int imx8mq_phy_power_on(struct phy *phy)
 	if (ret)
 		return ret;
 
-	return clk_prepare_enable(imx_phy->clk);
+	ret = clk_prepare_enable(imx_phy->clk);
+	if (ret)
+		return ret;
+
+	ret = clk_prepare_enable(imx_phy->alt_clk);
+	if (ret) {
+		clk_disable_unprepare(imx_phy->clk);
+		return ret;
+	}
+
+	return ret;
 }
 
 static int imx8mq_phy_power_off(struct phy *phy)
 {
 	struct imx8mq_usb_phy *imx_phy = phy_get_drvdata(phy);
 
+	clk_disable_unprepare(imx_phy->alt_clk);
 	clk_disable_unprepare(imx_phy->clk);
 	regulator_disable(imx_phy->vbus);
 
@@ -681,6 +695,11 @@ static int imx8mq_usb_phy_probe(struct platform_device *pdev)
 		return PTR_ERR(imx_phy->clk);
 	}
 
+	imx_phy->alt_clk = devm_clk_get_optional(dev, "alt");
+	if (IS_ERR(imx_phy->alt_clk))
+		return dev_err_probe(dev, PTR_ERR(imx_phy->alt_clk),
+				    "Failed to get alt clk\n");
+
 	imx_phy->base = devm_platform_ioremap_resource(pdev, 0);
 	if (IS_ERR(imx_phy->base))
 		return PTR_ERR(imx_phy->base);