[PATCH 2/5] usb: typec: tcpci: Receive SOP' only while sourcing VCONN

[Alexey Charkov]

A TCPC acks every message type enabled in RECEIVE_DETECT and passes it
on to TCPM. With SOP' enabled while the partner sources VCONN, the port
acks the partner's requests to the cable plug and the plug's replies to
the partner, colliding with the GoodCRC that the plug or the partner
sends. TCPM also tries to answer these messages as if they were destined
to it, which for the case of a partner's SOP' Discover Identity on a
HUSB311 made the partner soft reset the contract every time.

TCPM talks to the cable plug only while it is the VCONN Source, as USB
PD 3.0 section 6.3.11 requires, so listen for SOP' only then.

Switch SOP' reception off before VCONN goes off and on only once it is
on. If that fails, warn instead of failing the VCONN switch: SOP'
reception left off only costs cable discovery, and left on is no worse
than before this change.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 3bbb9ba4f660 ("usb: typec: tcpci: add tcpm_transmit_type to tcpm_pd_receive")
Signed-off-by: Alexey Charkov <alchark@xxxxxxxxxxx>
---
 drivers/usb/typec/tcpm/tcpci.c | 72 ++++++++++++++++++++++++++++--------------
 1 file changed, 49 insertions(+), 23 deletions(-)

diff --git a/drivers/usb/typec/tcpm/tcpci.c b/drivers/usb/typec/tcpm/tcpci.c
index 6717ac914c6a..af8db6b4497a 100644
--- a/drivers/usb/typec/tcpm/tcpci.c
+++ b/drivers/usb/typec/tcpm/tcpci.c
@@ -41,6 +41,7 @@ struct tcpci {
 	unsigned int rx_type_mask;
 
 	bool controls_vbus;
+	bool vconn_enabled;
 
 	struct tcpc_dev tcpc;
 	struct tcpci_data *data;
@@ -344,11 +345,45 @@ static void tcpci_set_partner_usb_comm_capable(struct tcpc_dev *tcpc, bool capab
 		tcpci->data->set_partner_usb_comm_capable(tcpci, tcpci->data, capable);
 }
 
+static int tcpci_set_pd_rx(struct tcpc_dev *tcpc, bool enable)
+{
+	struct tcpci *tcpci = tcpc_to_tcpci(tcpc);
+	unsigned int reg = 0;
+	int ret;
+
+	if (enable) {
+		reg = TCPC_RX_DETECT_SOP | TCPC_RX_DETECT_HARD_RESET;
+		/* Only the VCONN Source talks to the cable plug */
+		if (tcpci->data->cable_comm_capable && tcpci->vconn_enabled)
+			reg |= TCPC_RX_DETECT_SOP1;
+	}
+
+	tcpci->rx_type_mask = reg;
+	ret = regmap_write(tcpci->regmap, TCPC_RX_DETECT, reg);
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+
 static int tcpci_set_vconn(struct tcpc_dev *tcpc, bool enable)
 {
 	struct tcpci *tcpci = tcpc_to_tcpci(tcpc);
 	int ret;
 
+	/*
+	 * Without VCONN from us, SOP' traffic is between the partner and the
+	 * cable plug, and our GoodCRC would collide with theirs. So stop
+	 * receiving SOP' before VCONN goes off, and start only once it is on.
+	 * Neither is worth failing the VCONN switch over.
+	 */
+	if (!enable) {
+		tcpci->vconn_enabled = false;
+		if ((tcpci->rx_type_mask & TCPC_RX_DETECT_SOP1) &&
+		    tcpci_set_pd_rx(tcpc, true) < 0)
+			dev_warn(tcpci->dev, "Failed to disable SOP' reception\n");
+	}
+
 	/* Handle vendor set vconn */
 	if (tcpci->data->set_vconn) {
 		ret = tcpci->data->set_vconn(tcpci, tcpci->data, enable);
@@ -356,9 +391,20 @@ static int tcpci_set_vconn(struct tcpc_dev *tcpc, bool enable)
 			return ret;
 	}
 
-	return regmap_update_bits(tcpci->regmap, TCPC_POWER_CTRL,
-				TCPC_POWER_CTRL_VCONN_ENABLE,
-				enable ? TCPC_POWER_CTRL_VCONN_ENABLE : 0);
+	ret = regmap_update_bits(tcpci->regmap, TCPC_POWER_CTRL,
+				 TCPC_POWER_CTRL_VCONN_ENABLE,
+				 enable ? TCPC_POWER_CTRL_VCONN_ENABLE : 0);
+	if (ret < 0)
+		return ret;
+
+	if (enable) {
+		tcpci->vconn_enabled = true;
+		if (tcpci->data->cable_comm_capable && tcpci->rx_type_mask &&
+		    tcpci_set_pd_rx(tcpc, true) < 0)
+			dev_warn(tcpci->dev, "Failed to enable SOP' reception\n");
+	}
+
+	return 0;
 }
 
 static int tcpci_enable_auto_vbus_discharge(struct tcpc_dev *dev, bool enable)
@@ -478,26 +524,6 @@ static int tcpci_set_roles(struct tcpc_dev *tcpc, bool attached,
 	return 0;
 }
 
-static int tcpci_set_pd_rx(struct tcpc_dev *tcpc, bool enable)
-{
-	struct tcpci *tcpci = tcpc_to_tcpci(tcpc);
-	unsigned int reg = 0;
-	int ret;
-
-	if (enable) {
-		reg = TCPC_RX_DETECT_SOP | TCPC_RX_DETECT_HARD_RESET;
-		if (tcpci->data->cable_comm_capable)
-			reg |= TCPC_RX_DETECT_SOP1;
-	}
-
-	tcpci->rx_type_mask = reg;
-	ret = regmap_write(tcpci->regmap, TCPC_RX_DETECT, reg);
-	if (ret < 0)
-		return ret;
-
-	return 0;
-}
-
 static int tcpci_get_vbus(struct tcpc_dev *tcpc)
 {
 	struct tcpci *tcpci = tcpc_to_tcpci(tcpc);

-- 
2.56.0