phy: k1-usb: add disconnect function support

A disconnect status BIT of USB2 PHY need to be cleared, otherwise
it will fail to work properly during next connection when devices
connect to roothub directly.

Fixes: fe4bc1a ("phy: spacemit: support K1 USB2.0 PHY controller")
Signed-off-by: Yixun Lan <dlan@kernel.org>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Link: https://patch.msgid.link/20260216152653.25244-1-dlan@kernel.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>

Author: Yixun Lan

drivers/phy/spacemit/phy-k1-usb2.c

@@ -48,6 +48,9 @@
 #define  PHY_CLK_HSTXP_EN		BIT(3)		/* clock hstxp enable */
 #define  PHY_HSTXP_MODE			BIT(4)		/* 0: force en_txp to be 1; 1: no force */
 
+#define PHY_K1_HS_HOST_DISC		0x40
+#define  PHY_K1_HS_HOST_DISC_CLR		BIT(0)
+
 #define PHY_PLL_DIV_CFG			0x98
 #define  PHY_FDIV_FRACT_8_15		GENMASK(7, 0)
 #define  PHY_FDIV_FRACT_16_19		GENMASK(11, 8)
@@ -142,9 +145,20 @@ static int spacemit_usb2phy_exit(struct phy *phy)
 	return 0;
 }
 
+static int spacemit_usb2phy_disconnect(struct phy *phy, int port)
+{
+	struct spacemit_usb2phy *sphy = phy_get_drvdata(phy);
+
+	regmap_update_bits(sphy->regmap_base, PHY_K1_HS_HOST_DISC,
+			   PHY_K1_HS_HOST_DISC_CLR, PHY_K1_HS_HOST_DISC_CLR);
+
+	return 0;
+}
+
 static const struct phy_ops spacemit_usb2phy_ops = {
 	.init = spacemit_usb2phy_init,
 	.exit = spacemit_usb2phy_exit,
+	.disconnect = spacemit_usb2phy_disconnect,
 	.owner = THIS_MODULE,
 };