phy: cadence: salvo: decrease delay value to zero for txvalid

For USB2 L1 use cases, some hosts may start transferring less than 20us
after End of Resume, it causes the host seeing corrupt packet from the
device side. The reason is the delay time between PHY powers up and
txvalid is 20us. To fix it, we change the delay value as 0us.

Signed-off-by: Peter Chen <peter.chen@nxp.com>
Signed-off-by: Frank Li <Frank.Li@nxp.com>
Link: https://lore.kernel.org/r/20230517161646.3418250-3-Frank.Li@nxp.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

Author: Peter Chen

drivers/phy/cadence/phy-cadence-salvo.c

@@ -89,8 +89,20 @@
 #define TB_ADDR_XCVR_DIAG_LANE_FCM_EN_MGN_TMR	0x40f2
 #define TB_ADDR_TX_RCVDETSC_CTRL	        0x4124
 
+/* USB2 PHY register definition */
+#define UTMI_REG15				0xaf
+
 /* TB_ADDR_TX_RCVDETSC_CTRL */
 #define RXDET_IN_P3_32KHZ			BIT(0)
+/*
+ * UTMI_REG15
+ *
+ * Gate how many us for the txvalid signal until analog
+ * HS/FS transmitters have powered up
+ */
+#define TXVALID_GATE_THRESHOLD_HS_MASK		(BIT(4) | BIT(5))
+/* 0us, txvalid is ready just after HS/FS transmitters have powered up */
+#define TXVALID_GATE_THRESHOLD_HS_0US		(BIT(4) | BIT(5))
 
 struct cdns_reg_pairs {
 	u16 val;
@@ -230,6 +242,11 @@ static int cdns_salvo_phy_init(struct phy *phy)
 	cdns_salvo_write(salvo_phy, USB3_PHY_OFFSET, TB_ADDR_TX_RCVDETSC_CTRL,
 			 RXDET_IN_P3_32KHZ);
 
+	value = cdns_salvo_read(salvo_phy, USB2_PHY_OFFSET, UTMI_REG15);
+	value &= ~TXVALID_GATE_THRESHOLD_HS_MASK;
+	cdns_salvo_write(salvo_phy, USB2_PHY_OFFSET, UTMI_REG15,
+			 value | TXVALID_GATE_THRESHOLD_HS_0US);
+
 	udelay(10);
 
 	clk_disable_unprepare(salvo_phy->clk);