phy: phy-mtk-tphy: add property to set pre-emphasis

Add a property to set usb2 phy's pre-emphasis, it's disabled by default
on some SoCs.
Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20220914060746.10004-3-chunfeng.yun@mediatek.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

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

@@ -72,6 +72,8 @@
 #define PA5_RG_U2_HS_100U_U3_EN	BIT(11)
 
 #define U3P_USBPHYACR6		0x018
+#define PA6_RG_U2_PRE_EMP		GENMASK(31, 30)
+#define PA6_RG_U2_PRE_EMP_VAL(x)	((0x3 & (x)) << 30)
 #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)
@@ -370,6 +372,7 @@ struct mtk_phy_instance {
 	int eye_term;
 	int intr;
 	int discth;
+	int pre_emphasis;
 	bool bc12_en;
 };
 
@@ -841,10 +844,13 @@ static void phy_parse_property(struct mtk_tphy *tphy,
 				 &instance->intr);
 	device_property_read_u32(dev, "mediatek,discth",
 				 &instance->discth);
+	device_property_read_u32(dev, "mediatek,pre-emphasis",
+				 &instance->pre_emphasis);
 	dev_dbg(dev, "bc12:%d, src:%d, vrt:%d, term:%d, intr:%d, disc:%d\n",
 		instance->bc12_en, instance->eye_src,
 		instance->eye_vrt, instance->eye_term,
 		instance->intr, instance->discth);
+	dev_dbg(dev, "pre-emp:%d\n", instance->pre_emphasis);
 }
 
 static void u2_phy_props_set(struct mtk_tphy *tphy,
@@ -875,6 +881,10 @@ static void u2_phy_props_set(struct mtk_tphy *tphy,
 	if (instance->discth)
 		mtk_phy_update_bits(com + U3P_USBPHYACR6, PA6_RG_U2_DISCTH,
 				    PA6_RG_U2_DISCTH_VAL(instance->discth));
+
+	if (instance->pre_emphasis)
+		mtk_phy_update_bits(com + U3P_USBPHYACR6, PA6_RG_U2_PRE_EMP,
+				    PA6_RG_U2_PRE_EMP_VAL(instance->pre_emphasis));
 }
 
 /* type switch for usb3/pcie/sgmii/sata */