usb: typec: tcpm: add state machine support for SRC_VDM_IDENTITY_REQUEST

Add SRC_VDM_IDENTITY_REQUEST state which first enters after SRC_STARTUP.
The state sends Discover Identity on SOP' and transitions to
SRC_SEND_CAPABILITIES. SRC_SEND_CAPABILITIES will transition back into
SRC_VDM_IDENTITY_REQUEST instead of retrying immediately.
Signed-off-by: RD Babiera <rdbabiera@google.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20240108191620.987785-23-rdbabiera@google.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/typec/tcpm/tcpm.c

@@ -146,7 +146,9 @@
 	S(PORT_RESET_WAIT_OFF),			\
 						\
 	S(AMS_START),				\
-	S(CHUNK_NOT_SUPP)
+	S(CHUNK_NOT_SUPP),			\
+						\
+	S(SRC_VDM_IDENTITY_REQUEST)
 
 #define FOREACH_AMS(S)				\
 	S(NONE_AMS),				\
@@ -1963,6 +1965,7 @@ static int tcpm_pd_svdm(struct tcpm_port *port, struct typec_altmode *adev,
 					ret = tcpm_ams_start(port, VCONN_SWAP);
 					if (!ret)
 						return 0;
+					/* Cannot perform Vconn swap */
 					port->upcoming_state = INVALID_STATE;
 					port->send_discover_prime = false;
 				}
@@ -1994,6 +1997,16 @@ static int tcpm_pd_svdm(struct tcpm_port *port, struct typec_altmode *adev,
 				 * the svdm_version for the cable moving forward.
 				 */
 				svdm_consume_identity_sop_prime(port, p, cnt);
+
+				/*
+				 * If received in SRC_VDM_IDENTITY_REQUEST, continue
+				 * to SRC_SEND_CAPABILITIES
+				 */
+				if (port->state == SRC_VDM_IDENTITY_REQUEST) {
+					tcpm_set_state(port, SRC_SEND_CAPABILITIES, 0);
+					return 0;
+				}
+
 				*response_tx_sop_type = TCPC_TX_SOP;
 				response[0] = VDO(USB_SID_PD, 1,
 						  typec_get_negotiated_svdm_version(typec),
@@ -2288,7 +2301,8 @@ static void vdm_run_state_machine(struct tcpm_port *port)
 		 * if there's traffic or we're not in PDO ready state don't send
 		 * a VDM.
 		 */
-		if (port->state != SRC_READY && port->state != SNK_READY) {
+		if (port->state != SRC_READY && port->state != SNK_READY &&
+		    port->state != SRC_VDM_IDENTITY_REQUEST) {
 			port->vdm_sm_running = false;
 			break;
 		}
@@ -2364,13 +2378,22 @@ static void vdm_run_state_machine(struct tcpm_port *port)
 			tcpm_ams_finish(port);
 		break;
 	case VDM_STATE_ERR_SEND:
+		/*
+		 * When sending Discover Identity to SOP' before establishing an
+		 * explicit contract, do not retry. Instead, weave sending
+		 * Source_Capabilities over SOP and Discover Identity over SOP'.
+		 */
+		if (port->state == SRC_VDM_IDENTITY_REQUEST) {
+			tcpm_ams_finish(port);
+			port->vdm_state = VDM_STATE_DONE;
+			tcpm_set_state(port, SRC_SEND_CAPABILITIES, 0);
 		/*
 		 * A partner which does not support USB PD will not reply,
 		 * so this is not a fatal error. At the same time, some
 		 * devices may not return GoodCRC under some circumstances,
 		 * so we need to retry.
 		 */
-		if (port->vdm_retries < 3) {
+		} else if (port->vdm_retries < 3) {
 			tcpm_log(port, "VDM Tx error, retry");
 			port->vdm_retries++;
 			port->vdm_state = VDM_STATE_READY;
@@ -4478,8 +4501,12 @@ static void run_state_machine(struct tcpm_port *port)
 		}
 		ret = tcpm_pd_send_source_caps(port);
 		if (ret < 0) {
-			tcpm_set_state(port, SRC_SEND_CAPABILITIES,
-				       PD_T_SEND_SOURCE_CAP);
+			if (tcpm_can_communicate_sop_prime(port) &&
+			    IS_ERR_OR_NULL(port->cable))
+				tcpm_set_state(port, SRC_VDM_IDENTITY_REQUEST, 0);
+			else
+				tcpm_set_state(port, SRC_SEND_CAPABILITIES,
+					       PD_T_SEND_SOURCE_CAP);
 		} else {
 			/*
 			 * Per standard, we should clear the reset counter here.
@@ -5395,6 +5422,15 @@ static void run_state_machine(struct tcpm_port *port)
 		tcpm_pd_send_control(port, PD_CTRL_NOT_SUPP, TCPC_TX_SOP);
 		tcpm_set_state(port, port->pwr_role == TYPEC_SOURCE ? SRC_READY : SNK_READY, 0);
 		break;
+
+	/* Cable states */
+	case SRC_VDM_IDENTITY_REQUEST:
+		port->send_discover_prime = true;
+		port->tx_sop_type = TCPC_TX_SOP_PRIME;
+		mod_send_discover_delayed_work(port, 0);
+		port->upcoming_state = SRC_SEND_CAPABILITIES;
+		break;
+
 	default:
 		WARN(1, "Unexpected port state %d\n", port->state);
 		break;
@@ -6120,7 +6156,8 @@ static void tcpm_send_discover_work(struct kthread_work *work)
 	}
 
 	/* Retry if the port is not idle */
-	if ((port->state != SRC_READY && port->state != SNK_READY) || port->vdm_sm_running) {
+	if ((port->state != SRC_READY && port->state != SNK_READY &&
+	     port->state != SRC_VDM_IDENTITY_REQUEST) || port->vdm_sm_running) {
 		mod_send_discover_delayed_work(port, SEND_DISCOVER_RETRY_MS);
 		goto unlock;
 	}