[PATCH v3 05/12] usb: typec: tcpm: process receive and transmission of sop' messages

[RD Babiera <rdbabiera@google.com>]

Add negotiated revision and tx/rx message ids to tcpm_port specific to
SOP'. tx_sop_type is added to the tcpm_port to determine whether the
current constructed message will be sent over SOP or SOP' if not
sent immediately.

tcpm_pd_rx_handler updates the received message ids. SOP* messages are not
processed afterwards. The handler also calls tcpm_can_communicate_sop_prime
to determine if a SOP' message is directed towards the port, and drops SOP'
messages it should not respond to.

tcpm_can_communicate_sop_prime is added as a helper to determine whether
the port is capable of communicating over SOP' at a given moment. Being
the Vconn source is a requirement in Power Delivery 3.0 but only a
recommendation in Power Delviery 2.0. Because the port should ensure that
the cable is powered before communication, always enforce the port is the
Vconn source regardless of revision.

Signed-off-by: RD Babiera <rdbabiera@google.com>
---
Changes since v2:
* Fixed style errors, switch statements with TCPC_TX_SOP now combine
with default case.
---
 drivers/usb/typec/tcpm/tcpm.c | 145 +++++++++++++++++++++++++++++++---
 1 file changed, 134 insertions(+), 11 deletions(-)

diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
index ff0fcf560c88..d2ca85c8fec6 100644
--- a/drivers/usb/typec/tcpm/tcpm.c
+++ b/drivers/usb/typec/tcpm/tcpm.c
@@ -505,6 +505,35 @@ struct tcpm_port {
 	 * transitions.
 	 */
 	bool potential_contaminant;
+
+	/* SOP* Related Fields */
+	/*
+	 * tx_sop_type determines which SOP* a message is being sent on.
+	 * For messages that are queued and not sent immediately such as in
+	 * tcpm_queue_message or messages that send after state changes,
+	 * the tx_sop_type is set accordingly.
+	 */
+	enum tcpm_transmit_type tx_sop_type;
+	/*
+	 * Prior to discovering the port partner's Specification Revision, the
+	 * Vconn source and cable plug will use the lower of their two revisions.
+	 *
+	 * When the port partner's Specification Revision is discovered, the following
+	 * rules are put in place.
+	 *	1. If the cable revision (1) is lower than the revision negotiated
+	 * between the port and partner (2), the port and partner will communicate
+	 * on revision (2), but the port and cable will communicate on revision (1).
+	 *	2. If the cable revision (1) is higher than the revision negotiated
+	 * between the port and partner (2), the port and partner will communicate
+	 * on revision (2), and the port and cable will communicate on revision (2)
+	 * as well.
+	 */
+	unsigned int negotiated_rev_prime;
+	/*
+	 * Each SOP* type must maintain their own tx and rx message IDs
+	 */
+	unsigned int message_id_prime;
+	unsigned int rx_msgid_prime;
 #ifdef CONFIG_DEBUG_FS
 	struct dentry *dentry;
 	struct mutex logbuffer_lock;	/* log buffer access lock */
@@ -894,19 +923,30 @@ static void tcpm_ams_finish(struct tcpm_port *port)
 }
 
 static int tcpm_pd_transmit(struct tcpm_port *port,
-			    enum tcpm_transmit_type type,
+			    enum tcpm_transmit_type tx_sop_type,
 			    const struct pd_message *msg)
 {
 	unsigned long timeout;
 	int ret;
+	unsigned int negotiated_rev;
+
+	switch (tx_sop_type) {
+	case TCPC_TX_SOP_PRIME:
+		negotiated_rev = port->negotiated_rev_prime;
+		break;
+	case TCPC_TX_SOP:
+	default:
+		negotiated_rev = port->negotiated_rev;
+		break;
+	}
 
 	if (msg)
 		tcpm_log(port, "PD TX, header: %#x", le16_to_cpu(msg->header));
 	else
-		tcpm_log(port, "PD TX, type: %#x", type);
+		tcpm_log(port, "PD TX, type: %#x", tx_sop_type);
 
 	reinit_completion(&port->tx_complete);
-	ret = port->tcpc->pd_transmit(port->tcpc, type, msg, port->negotiated_rev);
+	ret = port->tcpc->pd_transmit(port->tcpc, tx_sop_type, msg, negotiated_rev);
 	if (ret < 0)
 		return ret;
 
@@ -919,7 +959,17 @@ static int tcpm_pd_transmit(struct tcpm_port *port,
 
 	switch (port->tx_status) {
 	case TCPC_TX_SUCCESS:
-		port->message_id = (port->message_id + 1) & PD_HEADER_ID_MASK;
+		switch (tx_sop_type) {
+		case TCPC_TX_SOP_PRIME:
+			port->message_id_prime = (port->message_id_prime + 1) &
+						 PD_HEADER_ID_MASK;
+			break;
+		case TCPC_TX_SOP:
+		default:
+			port->message_id = (port->message_id + 1) &
+					   PD_HEADER_ID_MASK;
+			break;
+		}
 		/*
 		 * USB PD rev 2.0, 8.3.2.2.1:
 		 * USB PD rev 3.0, 8.3.2.1.3:
@@ -1604,6 +1654,57 @@ static void tcpm_register_partner_altmodes(struct tcpm_port *port)
 
 #define supports_modal(port)	PD_IDH_MODAL_SUPP((port)->partner_ident.id_header)
 
+/*
+ * Helper to determine whether the port is capable of SOP' communication at the
+ * current point in time.
+ */
+static bool tcpm_can_communicate_sop_prime(struct tcpm_port *port)
+{
+	/* Check to see if tcpc supports SOP' communication */
+	if (!port->tcpc->cable_comm_capable || !port->tcpc->cable_comm_capable(port->tcpc))
+		return false;
+	/*
+	 * Power Delivery 2.0 Section 6.3.11
+	 * Before communicating with a Cable Plug a Port Should ensure that it
+	 * is the Vconn Source and that the Cable Plugs are powered by
+	 * performing a Vconn swap if necessary. Since it cannot be guaranteed
+	 * that the present Vconn Source is supplying Vconn, the only means to
+	 * ensure that the Cable Plugs are powered is for a Port wishing to
+	 * communicate with a Cable Plug is to become the Vconn Source.
+	 *
+	 * Power Delivery 3.0 Section 6.3.11
+	 * Before communicating with a Cable Plug a Port Shall ensure that it
+	 * is the Vconn source.
+	 */
+	if (port->vconn_role != TYPEC_SOURCE)
+		return false;
+	/*
+	 * Power Delivery 2.0 Section 2.4.4
+	 * When no Contract or an Implicit Contract is in place the Source can
+	 * communicate with a Cable Plug using SOP' packets in order to discover
+	 * its characteristics.
+	 *
+	 * Power Delivery 3.0 Section 2.4.4
+	 * When no Contract or an Implicit Contract is in place only the Source
+	 * port that is supplying Vconn is allowed to send packets to a Cable
+	 * Plug and is allowed to respond to packets from the Cable Plug.
+	 */
+	if (!port->explicit_contract)
+		return port->pwr_role == TYPEC_SOURCE;
+	if (port->negotiated_rev == PD_REV30)
+		return true;
+	/*
+	 * Power Delivery 2.0 Section 2.4.4
+	 *
+	 * When an Explicit Contract is in place the DFP (either the Source or
+	 * the Sink) can communicate with the Cable Plug(s) using SOP’/SOP”
+	 * Packets (see Figure 2-3).
+	 */
+	if (port->negotiated_rev == PD_REV20)
+		return port->data_role == TYPEC_HOST;
+	return false;
+}
+
 static int tcpm_pd_svdm(struct tcpm_port *port, struct typec_altmode *adev,
 			const u32 *p, int cnt, u32 *response,
 			enum adev_actions *adev_action)
@@ -2989,14 +3090,18 @@ static void tcpm_pd_rx_handler(struct kthread_work *work)
 	tcpm_log(port, "PD RX, header: %#x [%d]", le16_to_cpu(msg->header),
 		 port->attached);
 
-	/* Ignore SOP' for now */
-	if (rx_sop_type == TCPC_TX_SOP_PRIME)
-		goto done;
-
 	if (port->attached) {
 		enum pd_ctrl_msg_type type = pd_header_type_le(msg->header);
 		unsigned int msgid = pd_header_msgid_le(msg->header);
 
+		/*
+		 * Drop SOP' messages if cannot receive via
+		 * tcpm_can_communicate_sop_prime
+		 */
+		if (rx_sop_type == TCPC_TX_SOP_PRIME &&
+		    !tcpm_can_communicate_sop_prime(port))
+			goto done;
+
 		/*
 		 * USB PD standard, 6.6.1.2:
 		 * "... if MessageID value in a received Message is the
@@ -3006,16 +3111,27 @@ static void tcpm_pd_rx_handler(struct kthread_work *work)
 		 * Message). Note: this shall not apply to the Soft_Reset
 		 * Message which always has a MessageID value of zero."
 		 */
-		if (msgid == port->rx_msgid && type != PD_CTRL_SOFT_RESET)
+		switch (rx_sop_type) {
+		case TCPC_TX_SOP_PRIME:
+			if (msgid == port->rx_msgid_prime)
+				goto done;
+			port->rx_msgid_prime = msgid;
+			/* Ignore SOP' for now */
 			goto done;
-		port->rx_msgid = msgid;
+		case TCPC_TX_SOP:
+		default:
+			if (msgid == port->rx_msgid && type != PD_CTRL_SOFT_RESET)
+				goto done;
+			port->rx_msgid = msgid;
+			break;
+		}
 
 		/*
 		 * If both ends believe to be DFP/host, we have a data role
 		 * mismatch.
 		 */
 		if (!!(le16_to_cpu(msg->header) & PD_HEADER_DATA_ROLE) ==
-		    (port->data_role == TYPEC_HOST)) {
+		    (port->data_role == TYPEC_HOST) && rx_sop_type == TCPC_TX_SOP) {
 			tcpm_log(port,
 				 "Data role mismatch, initiating error recovery");
 			tcpm_set_state(port, ERROR_RECOVERY, 0);
@@ -3720,6 +3836,7 @@ static void tcpm_reset_port(struct tcpm_port *port)
 	 * we can check tcpm_pd_rx_handler() if we had seen it before.
 	 */
 	port->rx_msgid = -1;
+	port->rx_msgid_prime = -1;
 
 	port->tcpc->set_pd_rx(port->tcpc, false);
 	tcpm_init_vbus(port);	/* also disables charging */
@@ -4034,8 +4151,11 @@ static void run_state_machine(struct tcpm_port *port)
 		port->pwr_opmode = TYPEC_PWR_MODE_USB;
 		port->caps_count = 0;
 		port->negotiated_rev = PD_MAX_REV;
+		port->negotiated_rev_prime = PD_MAX_REV;
 		port->message_id = 0;
+		port->message_id_prime = 0;
 		port->rx_msgid = -1;
+		port->rx_msgid_prime = -1;
 		port->explicit_contract = false;
 		/* SNK -> SRC POWER/FAST_ROLE_SWAP finished */
 		if (port->ams == POWER_ROLE_SWAP ||
@@ -4275,8 +4395,11 @@ static void run_state_machine(struct tcpm_port *port)
 		typec_set_pwr_opmode(port->typec_port, opmode);
 		port->pwr_opmode = TYPEC_PWR_MODE_USB;
 		port->negotiated_rev = PD_MAX_REV;
+		port->negotiated_rev_prime = PD_MAX_REV;
 		port->message_id = 0;
+		port->message_id_prime = 0;
 		port->rx_msgid = -1;
+		port->rx_msgid_prime = -1;
 		port->explicit_contract = false;
 
 		if (port->ams == POWER_ROLE_SWAP ||
-- 
2.43.0.472.g3155946c3a-goog