usb: typec: tcpci: Add support when hidden tx registers are inaccessible

TCPCI spec forbids direct access of TX_BUF_BYTE_x register.
The existing version of tcpci driver assumes that those registers
are directly addressible. Add support for tcpci chips which do
not support direct access to TX_BUF_BYTE_x registers. TX_BUF_BYTE_x
can only be accessed by I2C_WRITE_BYTE_COUNT.
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
Link: https://lore.kernel.org/r/20200901025927.3596190-3-badhri@google.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/typec/tcpm/tcpci.c

@@ -330,23 +330,47 @@ static int tcpci_pd_transmit(struct tcpc_dev *tcpc,
 	int ret;
 
 	cnt = msg ? pd_header_cnt(header) * 4 : 0;
-	ret = regmap_write(tcpci->regmap, TCPC_TX_BYTE_CNT, cnt + 2);
-	if (ret < 0)
-		return ret;
+	/**
+	 * TCPCI spec forbids direct access of TCPC_TX_DATA.
+	 * But, since some of the chipsets offer this capability,
+	 * it's fair to support both.
+	 */
+	if (tcpci->data->TX_BUF_BYTE_x_hidden) {
+		u8 buf[TCPC_TRANSMIT_BUFFER_MAX_LEN] = {0,};
+		u8 pos = 0;
 
-	ret = tcpci_write16(tcpci, TCPC_TX_HDR, header);
-	if (ret < 0)
-		return ret;
+		/* Payload + header + TCPC_TX_BYTE_CNT */
+		buf[pos++] = cnt + 2;
+
+		if (msg)
+			memcpy(&buf[pos], &msg->header, sizeof(msg->header));
+
+		pos += sizeof(header);
 
-	if (cnt > 0) {
-		ret = regmap_raw_write(tcpci->regmap, TCPC_TX_DATA,
-				       &msg->payload, cnt);
+		if (cnt > 0)
+			memcpy(&buf[pos], msg->payload, cnt);
+
+		pos += cnt;
+		ret = regmap_raw_write(tcpci->regmap, TCPC_TX_BYTE_CNT, buf, pos);
+		if (ret < 0)
+			return ret;
+	} else {
+		ret = regmap_write(tcpci->regmap, TCPC_TX_BYTE_CNT, cnt + 2);
 		if (ret < 0)
 			return ret;
+
+		ret = tcpci_write16(tcpci, TCPC_TX_HDR, header);
+		if (ret < 0)
+			return ret;
+
+		if (cnt > 0) {
+			ret = regmap_raw_write(tcpci->regmap, TCPC_TX_DATA, &msg->payload, cnt);
+			if (ret < 0)
+				return ret;
+		}
 	}
 
-	reg = (PD_RETRY_COUNT << TCPC_TRANSMIT_RETRY_SHIFT) |
-		(type << TCPC_TRANSMIT_TYPE_SHIFT);
+	reg = (PD_RETRY_COUNT << TCPC_TRANSMIT_RETRY_SHIFT) | (type << TCPC_TRANSMIT_TYPE_SHIFT);
 	ret = regmap_write(tcpci->regmap, TCPC_TRANSMIT, reg);
 	if (ret < 0)
 		return ret;

drivers/usb/typec/tcpm/tcpci.h

@@ -128,9 +128,17 @@
 #define TCPC_VBUS_VOLTAGE_ALARM_HI_CFG		0x76
 #define TCPC_VBUS_VOLTAGE_ALARM_LO_CFG		0x78
 
+/* I2C_WRITE_BYTE_COUNT + 1 when TX_BUF_BYTE_x is only accessible I2C_WRITE_BYTE_COUNT */
+#define TCPC_TRANSMIT_BUFFER_MAX_LEN		31
+
+/*
+ * @TX_BUF_BYTE_x_hidden
+ *		optional; Set when TX_BUF_BYTE_x can only be accessed through I2C_WRITE_BYTE_COUNT.
+ */
 struct tcpci;
 struct tcpci_data {
 	struct regmap *regmap;
+	unsigned char TX_BUF_BYTE_x_hidden:1;
 	int (*init)(struct tcpci *tcpci, struct tcpci_data *data);
 	int (*set_vconn)(struct tcpci *tcpci, struct tcpci_data *data,
 			 bool enable);