[PATCH v3] usb: typec: tcpci: don't touch CC line if it's Vconn source

[Xu Yang <xu.yang_2@xxxxxxx>]

With the AMS and Collision Avoidance, tcpm often needs to change the CC's
termination. When one CC line is sourcing Vconn, if we still change its
termination, the voltage of the another CC line is likely to be fluctuant
and unstable.

Therefore, we should verify whether a CC line is sourcing Vconn before
changing its termination and only change the termination that is not
a Vconn line. This can be done by reading the Vconn Present bit of
POWER_ STATUS register. To determine the polarity, we can read the
Plug Orientation bit of TCPC_CONTROL register. Since Vconn can only be
sourced if Plug Orientation is set.

Fixes: 0908c5aca31e ("usb: typec: tcpm: AMS and Collision Avoidance")
cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Xu Yang <xu.yang_2@xxxxxxx>

---
v2: changed subject line
v3: optimized the commit message and code according to Guenter's suggestions
---
 drivers/usb/typec/tcpm/tcpci.c | 26 ++++++++++++++++++++++++++
 drivers/usb/typec/tcpm/tcpci.h |  1 +
 2 files changed, 27 insertions(+)

diff --git a/drivers/usb/typec/tcpm/tcpci.c b/drivers/usb/typec/tcpm/tcpci.c
index 35a1307349a2..e07d26a3cd8e 100644
--- a/drivers/usb/typec/tcpm/tcpci.c
+++ b/drivers/usb/typec/tcpm/tcpci.c
@@ -75,9 +75,25 @@ static int tcpci_write16(struct tcpci *tcpci, unsigned int reg, u16 val)
 static int tcpci_set_cc(struct tcpc_dev *tcpc, enum typec_cc_status cc)
 {
 	struct tcpci *tcpci = tcpc_to_tcpci(tcpc);
+	bool vconn_pres;
+	enum typec_cc_polarity polarity = TYPEC_POLARITY_CC1;
 	unsigned int reg;
 	int ret;
 
+	ret = regmap_read(tcpci->regmap, TCPC_POWER_STATUS, &reg);
+	if (ret < 0)
+		return ret;
+
+	vconn_pres = !!(reg & TCPC_POWER_STATUS_VCONN_PRES);
+	if (vconn_pres) {
+		ret = regmap_read(tcpci->regmap, TCPC_TCPC_CTRL, &reg);
+		if (ret < 0)
+			return ret;
+
+		if (reg & TCPC_TCPC_CTRL_ORIENTATION)
+			polarity = TYPEC_POLARITY_CC2;
+	}
+
 	switch (cc) {
 	case TYPEC_CC_RA:
 		reg = (TCPC_ROLE_CTRL_CC_RA << TCPC_ROLE_CTRL_CC1_SHIFT) |
@@ -112,6 +128,16 @@ static int tcpci_set_cc(struct tcpc_dev *tcpc, enum typec_cc_status cc)
 		break;
 	}
 
+	if (vconn_pres) {
+		if (polarity == TYPEC_POLARITY_CC2) {
+			reg &= ~(TCPC_ROLE_CTRL_CC1_MASK << TCPC_ROLE_CTRL_CC1_SHIFT);
+			reg |= (TCPC_ROLE_CTRL_CC_OPEN << TCPC_ROLE_CTRL_CC1_SHIFT);
+		} else {
+			reg &= ~(TCPC_ROLE_CTRL_CC2_MASK << TCPC_ROLE_CTRL_CC2_SHIFT);
+			reg |= (TCPC_ROLE_CTRL_CC_OPEN << TCPC_ROLE_CTRL_CC2_SHIFT);
+		}
+	}
+
 	ret = regmap_write(tcpci->regmap, TCPC_ROLE_CTRL, reg);
 	if (ret < 0)
 		return ret;
diff --git a/drivers/usb/typec/tcpm/tcpci.h b/drivers/usb/typec/tcpm/tcpci.h
index 2be7a77d400e..b2edd45f13c6 100644
--- a/drivers/usb/typec/tcpm/tcpci.h
+++ b/drivers/usb/typec/tcpm/tcpci.h
@@ -98,6 +98,7 @@
 #define TCPC_POWER_STATUS_SOURCING_VBUS	BIT(4)
 #define TCPC_POWER_STATUS_VBUS_DET	BIT(3)
 #define TCPC_POWER_STATUS_VBUS_PRES	BIT(2)
+#define TCPC_POWER_STATUS_VCONN_PRES	BIT(1)
 #define TCPC_POWER_STATUS_SINKING_VBUS	BIT(0)
 
 #define TCPC_FAULT_STATUS		0x1f
-- 
2.25.1