usb: typec: tcpm: Relax disconnect threshold during power negotiation

If the voltage is being decreased in power negotiation, the Source will
set the power supply to operate at the new voltage level before sending
PS_RDY. Relax the threshold before sending Request Message so that it
will not race with Source which begins to adjust the voltage right after
it sends Accept Message (PPS) or tSrcTransition (25~35ms) after it sends
Accept Message (non-PPS).

The real threshold will be set after Sink receives PS_RDY Message.

Fixes: f321a02c ("usb: typec: tcpm: Implement enabling Auto Discharge disconnect support")
Cc: stable <stable@vger.kernel.org>
Cc: Badhri Jagan Sridharan <badhri@google.com>
Reviewed-by: Badhri Jagan Sridharan <badhri@google.com>
Acked-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Kyle Tso <kyletso@google.com>
Link: https://lore.kernel.org/r/20210616090102.1897674-1-kyletso@google.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/typec/tcpm/tcpm.c

@@ -2604,6 +2604,11 @@ static void tcpm_pd_ctrl_request(struct tcpm_port *port,
 			} else {
 				next_state = SNK_WAIT_CAPABILITIES;
 			}
+
+			/* Threshold was relaxed before sending Request. Restore it back. */
+			tcpm_set_auto_vbus_discharge_threshold(port, TYPEC_PWR_MODE_PD,
+							       port->pps_data.active,
+							       port->supply_voltage);
 			tcpm_set_state(port, next_state, 0);
 			break;
 		case SNK_NEGOTIATE_PPS_CAPABILITIES:
@@ -2617,6 +2622,11 @@ static void tcpm_pd_ctrl_request(struct tcpm_port *port,
 			    port->send_discover)
 				port->vdm_sm_running = true;
 
+			/* Threshold was relaxed before sending Request. Restore it back. */
+			tcpm_set_auto_vbus_discharge_threshold(port, TYPEC_PWR_MODE_PD,
+							       port->pps_data.active,
+							       port->supply_voltage);
+
 			tcpm_set_state(port, SNK_READY, 0);
 			break;
 		case DR_SWAP_SEND:
@@ -3336,6 +3346,12 @@ static int tcpm_pd_send_request(struct tcpm_port *port)
 	if (ret < 0)
 		return ret;
 
+	/*
+	 * Relax the threshold as voltage will be adjusted after Accept Message plus tSrcTransition.
+	 * It is safer to modify the threshold here.
+	 */
+	tcpm_set_auto_vbus_discharge_threshold(port, TYPEC_PWR_MODE_USB, false, 0);
+
 	memset(&msg, 0, sizeof(msg));
 	msg.header = PD_HEADER_LE(PD_DATA_REQUEST,
 				  port->pwr_role,
@@ -3433,6 +3449,9 @@ static int tcpm_pd_send_pps_request(struct tcpm_port *port)
 	if (ret < 0)
 		return ret;
 
+	/* Relax the threshold as voltage will be adjusted right after Accept Message. */
+	tcpm_set_auto_vbus_discharge_threshold(port, TYPEC_PWR_MODE_USB, false, 0);
+
 	memset(&msg, 0, sizeof(msg));
 	msg.header = PD_HEADER_LE(PD_DATA_REQUEST,
 				  port->pwr_role,
@@ -4196,6 +4215,10 @@ static void run_state_machine(struct tcpm_port *port)
 		port->hard_reset_count = 0;
 		ret = tcpm_pd_send_request(port);
 		if (ret < 0) {
+			/* Restore back to the original state */
+			tcpm_set_auto_vbus_discharge_threshold(port, TYPEC_PWR_MODE_PD,
+							       port->pps_data.active,
+							       port->supply_voltage);
 			/* Let the Source send capabilities again. */
 			tcpm_set_state(port, SNK_WAIT_CAPABILITIES, 0);
 		} else {
@@ -4206,6 +4229,10 @@ static void run_state_machine(struct tcpm_port *port)
 	case SNK_NEGOTIATE_PPS_CAPABILITIES:
 		ret = tcpm_pd_send_pps_request(port);
 		if (ret < 0) {
+			/* Restore back to the original state */
+			tcpm_set_auto_vbus_discharge_threshold(port, TYPEC_PWR_MODE_PD,
+							       port->pps_data.active,
+							       port->supply_voltage);
 			port->pps_status = ret;
 			/*
 			 * If this was called due to updates to sink