[PATCH 2/3] usb: typec: tcpm: Add functions to read the VBUS voltage

[Angus Ainslie (Purism)]

Put some diagnostics in the tcpm log when there's an over
or under voltage situation.

Signed-off-by: Angus Ainslie (Purism) <angus@xxxxxxxx>
---
 drivers/usb/typec/tcpm/tcpci.c | 44 ++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/drivers/usb/typec/tcpm/tcpci.c b/drivers/usb/typec/tcpm/tcpci.c
index c1f7073a56de..c6e0e48b9a2a 100644
--- a/drivers/usb/typec/tcpm/tcpci.c
+++ b/drivers/usb/typec/tcpm/tcpci.c
@@ -261,6 +261,39 @@ static int tcpci_set_pd_rx(struct tcpc_dev *tcpc, bool enable)
 	return 0;
 }
 
+static int tcpci_get_vbus_voltage(struct tcpc_dev *tcpc)
+{
+	struct tcpci *tcpci = tcpc_to_tcpci(tcpc);
+	u16 vbus_reg;
+	unsigned int vbus_voltage;
+	int ret, scale;
+
+	ret = tcpci_read16(tcpci, TCPC_VBUS_VOLTAGE, &vbus_reg);
+	if (ret < 0)
+		return ret;
+
+	vbus_voltage = vbus_reg & 0x3f;
+	switch ((ret >> 10) & 3) {
+	case 0:
+		scale = 1;
+		break;
+	case 1:
+		scale = 2;
+		break;
+	case 2:
+		scale = 4;
+		break;
+	case 3:
+		tcpm_log(tcpci->port, "invalid VBUS scale");
+		return -1;
+	}
+
+	if (scale != 1)
+		vbus_voltage *= scale;
+
+	return vbus_voltage;
+}
+
 static int tcpci_get_vbus(struct tcpc_dev *tcpc)
 {
 	struct tcpci *tcpci = tcpc_to_tcpci(tcpc);
@@ -463,6 +496,17 @@ irqreturn_t tcpci_irq(struct tcpci *tcpci)
 	else if (status & TCPC_ALERT_TX_FAILED)
 		tcpm_pd_transmit_complete(tcpci->port, TCPC_TX_FAILED);
 
+	if (status & (TCPC_ALERT_V_ALARM_LO | TCPC_ALERT_V_ALARM_HI)) {
+		int ret;
+
+		ret = tcpci_get_vbus_voltage(&tcpci->tcpc);
+
+		if (IS_ERR(ret))
+			tcpm_log(tcpci->port, "Can't read VBUS voltage");
+		else
+			tcpm_log(tcpci->port, "Invalid VBUS voltage %d", ret);
+	}
+
 	return IRQ_HANDLED;
 }
 EXPORT_SYMBOL_GPL(tcpci_irq);
-- 
2.17.1