usb: typec: tcpm: Implement enabling Auto Discharge disconnect support

TCPCI spec allows TCPC hardware to autonomously discharge the vbus
capacitance upon disconnect. The expectation is that the TCPM enables
AutoDischargeDisconnect while entering SNK/SRC_ATTACHED states. Hardware
then automously discharges vbus when the vbus falls below a certain
threshold i.e. VBUS_SINK_DISCONNECT_THRESHOLD.

Apart from enabling the vbus discharge circuit, AutoDischargeDisconnect
is also used a flag to move TCPCI based TCPC implementations into
Attached.Snk/Attached.Src state as mentioned in
Figure 4-15. TCPC State Diagram before a Connection of the
USB Type-C Port Controller Interface Specification.
In such TCPC implementations, setting AutoDischargeDisconnect would
prevent TCPC into entering "Connection_Invalid" state as well.

Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20201029063138.1429760-8-badhri@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/typec/tcpm/tcpm.c

@@ -1706,6 +1706,24 @@ static void tcpm_handle_alert(struct tcpm_port *port, const __le32 *payload,
 	}
 }
 
+static int tcpm_set_auto_vbus_discharge_threshold(struct tcpm_port *port,
+						  enum typec_pwr_opmode mode, bool pps_active,
+						  u32 requested_vbus_voltage)
+{
+	int ret;
+
+	if (!port->tcpc->set_auto_vbus_discharge_threshold)
+		return 0;
+
+	ret = port->tcpc->set_auto_vbus_discharge_threshold(port->tcpc, mode, pps_active,
+							    requested_vbus_voltage);
+	tcpm_log_force(port,
+		       "set_auto_vbus_discharge_threshold mode:%d pps_active:%c vbus:%u ret:%d",
+		       mode, pps_active ? 'y' : 'n', requested_vbus_voltage, ret);
+
+	return ret;
+}
+
 static void tcpm_pd_data_request(struct tcpm_port *port,
 				 const struct pd_message *msg)
 {
@@ -1876,6 +1894,10 @@ static void tcpm_pd_ctrl_request(struct tcpm_port *port,
 						       port->current_limit,
 						       port->supply_voltage);
 				port->explicit_contract = true;
+				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);
 			} else {
 				/*
@@ -2790,8 +2812,12 @@ static int tcpm_src_attach(struct tcpm_port *port)
 	if (ret < 0)
 		return ret;
 
-	ret = tcpm_set_roles(port, true, TYPEC_SOURCE,
+	if (port->tcpc->enable_auto_vbus_discharge) {
-			     tcpm_data_role_for_source(port));
+		ret = port->tcpc->enable_auto_vbus_discharge(port->tcpc, true);
+		tcpm_log_force(port, "enable vbus discharge ret:%d", ret);
+	}
+
+	ret = tcpm_set_roles(port, true, TYPEC_SOURCE, tcpm_data_role_for_source(port));
 	if (ret < 0)
 		return ret;
 
@@ -2858,6 +2884,12 @@ static void tcpm_unregister_altmodes(struct tcpm_port *port)
 
 static void tcpm_reset_port(struct tcpm_port *port)
 {
+	int ret;
+
+	if (port->tcpc->enable_auto_vbus_discharge) {
+		ret = port->tcpc->enable_auto_vbus_discharge(port->tcpc, false);
+		tcpm_log_force(port, "Disable vbus discharge ret:%d", ret);
+	}
 	tcpm_unregister_altmodes(port);
 	tcpm_typec_disconnect(port);
 	port->attached = false;
@@ -2922,8 +2954,13 @@ static int tcpm_snk_attach(struct tcpm_port *port)
 	if (ret < 0)
 		return ret;
 
-	ret = tcpm_set_roles(port, true, TYPEC_SINK,
+	if (port->tcpc->enable_auto_vbus_discharge) {
-			     tcpm_data_role_for_sink(port));
+		tcpm_set_auto_vbus_discharge_threshold(port, TYPEC_PWR_MODE_USB, false, VSAFE5V);
+		ret = port->tcpc->enable_auto_vbus_discharge(port->tcpc, true);
+		tcpm_log_force(port, "enable vbus discharge ret:%d", ret);
+	}
+
+	ret = tcpm_set_roles(port, true, TYPEC_SINK, tcpm_data_role_for_sink(port));
 	if (ret < 0)
 		return ret;
 
@@ -3507,6 +3544,8 @@ static void run_state_machine(struct tcpm_port *port)
 		tcpm_set_state(port, SRC_UNATTACHED, PD_T_PS_SOURCE_ON);
 		break;
 	case SNK_HARD_RESET_SINK_OFF:
+		/* Do not discharge/disconnect during hard reseet */
+		tcpm_set_auto_vbus_discharge_threshold(port, TYPEC_PWR_MODE_USB, false, 0);
 		memset(&port->pps_data, 0, sizeof(port->pps_data));
 		tcpm_set_vconn(port, false);
 		if (port->pd_capable)
@@ -3549,6 +3588,7 @@ static void run_state_machine(struct tcpm_port *port)
 			tcpm_set_charge(port, true);
 		}
 		tcpm_set_attached_state(port, true);
+		tcpm_set_auto_vbus_discharge_threshold(port, TYPEC_PWR_MODE_USB, false, VSAFE5V);
 		tcpm_set_state(port, SNK_STARTUP, 0);
 		break;
 
@@ -3650,6 +3690,10 @@ static void run_state_machine(struct tcpm_port *port)
 			tcpm_set_state(port, PR_SWAP_SNK_SRC_SINK_OFF, 0);
 		break;
 	case PR_SWAP_SRC_SNK_TRANSITION_OFF:
+		/*
+		 * Prevent vbus discharge circuit from turning on during PR_SWAP
+		 * as this is not a disconnect.
+		 */
 		tcpm_set_vbus(port, false);
 		port->explicit_contract = false;
 		/* allow time for Vbus discharge, must be < tSrcSwapStdby */
@@ -3678,9 +3722,17 @@ static void run_state_machine(struct tcpm_port *port)
 		tcpm_set_state_cond(port, SNK_UNATTACHED, PD_T_PS_SOURCE_ON);
 		break;
 	case PR_SWAP_SRC_SNK_SINK_ON:
+		/* Set the vbus disconnect threshold for implicit contract */
+		tcpm_set_auto_vbus_discharge_threshold(port, TYPEC_PWR_MODE_USB, false, VSAFE5V);
 		tcpm_set_state(port, SNK_STARTUP, 0);
 		break;
 	case PR_SWAP_SNK_SRC_SINK_OFF:
+		/*
+		 * Prevent vbus discharge circuit from turning on during PR_SWAP
+		 * as this is not a disconnect.
+		 */
+		tcpm_set_auto_vbus_discharge_threshold(port, TYPEC_PWR_MODE_USB,
+						       port->pps_data.active, 0);
 		tcpm_set_charge(port, false);
 		tcpm_set_state(port, hard_reset_state(port),
 			       PD_T_PS_SOURCE_OFF);

include/linux/usb/tcpm.h

@@ -86,6 +86,18 @@ enum tcpm_transmit_type {
  * @frs_sourcing_vbus:
  *		Optional; Called to notify that vbus is now being sourced.
  *		Low level drivers can perform chip specific operations, if any.
+ * @enable_auto_vbus_discharge:
+ *		Optional; TCPCI spec based TCPC implementations can optionally
+ *		support hardware to autonomously dischrge vbus upon disconnecting
+ *		as sink or source. TCPM signals TCPC to enable the mechanism upon
+ *		entering connected state and signals disabling upon disconnect.
+ * @set_auto_vbus_discharge_threshold:
+ *		Mandatory when enable_auto_vbus_discharge is implemented. TCPM
+ *		calls this function to allow lower levels drivers to program the
+ *		vbus threshold voltage below which the vbus discharge circuit
+ *		will be turned on. requested_vbus_voltage is set to 0 when vbus
+ *		is going to disappear knowingly i.e. during PR_SWAP and
+ *		HARD_RESET etc.
  */
 struct tcpc_dev {
 	struct fwnode_handle *fwnode;
@@ -113,6 +125,9 @@ struct tcpc_dev {
 	int (*set_bist_data)(struct tcpc_dev *dev, bool on);
 	int (*enable_frs)(struct tcpc_dev *dev, bool enable);
 	void (*frs_sourcing_vbus)(struct tcpc_dev *dev);
+	int (*enable_auto_vbus_discharge)(struct tcpc_dev *dev, bool enable);
+	int (*set_auto_vbus_discharge_threshold)(struct tcpc_dev *dev, enum typec_pwr_opmode mode,
+						 bool pps_active, u32 requested_vbus_voltage);
 };
 
 struct tcpm_port;