phy: phy-mtk-tphy: add a property for disconnect threshold

This is used to tune the threshold of disconnect, the index range
is [0, 15], the threshold voltage is about 400mV for 0, 700mV for
15, and the step is 20mV.
Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>

drivers/phy/mediatek/phy-mtk-tphy.c

@@ -60,6 +60,8 @@
 #define U3P_USBPHYACR6		0x018
 #define PA6_RG_U2_BC11_SW_EN		BIT(23)
 #define PA6_RG_U2_OTG_VBUSCMP_EN	BIT(20)
+#define PA6_RG_U2_DISCTH		GENMASK(7, 4)
+#define PA6_RG_U2_DISCTH_VAL(x)	((0xf & (x)) << 4)
 #define PA6_RG_U2_SQTH		GENMASK(3, 0)
 #define PA6_RG_U2_SQTH_VAL(x)	(0xf & (x))
 
@@ -300,6 +302,7 @@ struct mtk_phy_instance {
 	int eye_src;
 	int eye_vrt;
 	int eye_term;
+	int discth;
 	bool bc12_en;
 };
 
@@ -850,9 +853,12 @@ static void phy_parse_property(struct mtk_tphy *tphy,
 				 &instance->eye_vrt);
 	device_property_read_u32(dev, "mediatek,eye-term",
 				 &instance->eye_term);
-	dev_dbg(dev, "bc12:%d, src:%d, vrt:%d, term:%d\n",
+	device_property_read_u32(dev, "mediatek,discth",
+				 &instance->discth);
+	dev_dbg(dev, "bc12:%d, src:%d, vrt:%d, term:%d, disc:%d\n",
 		instance->bc12_en, instance->eye_src,
-		instance->eye_vrt, instance->eye_term);
+		instance->eye_vrt, instance->eye_term,
+		instance->discth);
 }
 
 static void u2_phy_props_set(struct mtk_tphy *tphy,
@@ -888,6 +894,13 @@ static void u2_phy_props_set(struct mtk_tphy *tphy,
 		tmp |= PA1_RG_TERM_SEL_VAL(instance->eye_term);
 		writel(tmp, com + U3P_USBPHYACR1);
 	}
+
+	if (instance->discth) {
+		tmp = readl(com + U3P_USBPHYACR6);
+		tmp &= ~PA6_RG_U2_DISCTH;
+		tmp |= PA6_RG_U2_DISCTH_VAL(instance->discth);
+		writel(tmp, com + U3P_USBPHYACR6);
+	}
 }
 
 static int mtk_phy_init(struct phy *phy)