usb_pd_protocol: tcpm_get_message: Check return value

We currently rely on *head == 0 as error condition, which is
fragile and inconsistent across TCPCs implementations.

Instead, let's return a proper return value on all implementations.

BRANCH=none
BUG=chrome-os-partner:60575
TEST=elm FW as of 65fb80d (later version include a fix that would
     hide this issue), cherry-pick this patch, connect j5create
     adapter, then HDMI, then power => no crash

Change-Id: If7235e0491e9f80fdd50ce2605477ee518f8e1aa
Reviewed-on: https://chromium-review.googlesource.com/417443
Commit-Ready: Nicolas Boichat <drinkcat@chromium.org>
Tested-by: Nicolas Boichat <drinkcat@chromium.org>
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>

4 files changed, 9 insertions, 13 deletions

diff --git a/common/usb_pd_protocol.c b/common/usb_pd_protocol.c
index 3ea1dbf723..e50bc7f734 100644
--- a/common/usb_pd_protocol.c
+++ b/common/usb_pd_protocol.c
@@ -1698,8 +1698,7 @@ void pd_task(void)
 		/* process any potential incoming message */
 		incoming_packet = evt & PD_EVENT_RX;
 		if (incoming_packet) {
-			tcpm_get_message(port, payload, &head);
-			if (head > 0)
+			if (!tcpm_get_message(port, payload, &head))
 				handle_request(port, head, payload);
 		}
 		/* if nothing to do, verify the state of the world in 500ms */
diff --git a/driver/tcpm/anx74xx.c b/driver/tcpm/anx74xx.c
index 89f187f44b..08525a0d08 100644
--- a/driver/tcpm/anx74xx.c
+++ b/driver/tcpm/anx74xx.c
@@ -717,7 +717,6 @@ static int anx74xx_tcpm_get_message(int port, uint32_t *payload, int *head)
 	/* Fetch the header */
 	rv |= tcpc_read16(port, ANX74XX_REG_PD_HEADER, &reg);
 	if (rv) {
-		*head = 0;
 		clear_recvd_msg_int(port);
 		return EC_ERROR_UNKNOWN;
 	}
@@ -726,17 +725,15 @@ static int anx74xx_tcpm_get_message(int port, uint32_t *payload, int *head)
 	len = PD_HEADER_CNT(*head) * 4;
 	if (!len) {
 		clear_recvd_msg_int(port);
-	return EC_SUCCESS;
+		return EC_SUCCESS;
 	}
 
 	/* Receive message : assuming payload have enough
 	 * memory allocated
 	 */
 	rv |= anx74xx_read_pd_obj(port, (uint8_t *)payload, len);
-	if (rv) {
-		*head = 0;
+	if (rv)
 		return EC_ERROR_UNKNOWN;
-	}
 
 	return rv;
 }
diff --git a/driver/tcpm/it83xx.c b/driver/tcpm/it83xx.c
index 66e4dd1502..d31a00ecec 100644
--- a/driver/tcpm/it83xx.c
+++ b/driver/tcpm/it83xx.c
@@ -93,13 +93,12 @@ static enum tcpc_cc_voltage_status it83xx_get_cc(
 	return cc_state;
 }
 
-static void it83xx_rx_data(enum usbpd_port port, int *head, uint32_t *buf)
+static int it83xx_rx_data(enum usbpd_port port, int *head, uint32_t *buf)
 {
 	struct usbpd_header *p_head = (struct usbpd_header *)head;
-	*head = 0;
 
 	if (!USBPD_IS_RX_DONE(port))
-		return;
+		return EC_ERROR_UNKNOWN;
 
 	/* store header */
 	*p_head = *((struct usbpd_header *)IT83XX_USBPD_RMH_BASE(port));
@@ -113,6 +112,8 @@ static void it83xx_rx_data(enum usbpd_port port, int *head, uint32_t *buf)
 	 * If clear this bit, USBPD receives next packet
 	 */
 	IT83XX_USBPD_MRSR(port) = USBPD_REG_MASK_RX_MSG_VALID;
+
+	return EC_SUCCESS;
 }
 
 static enum tcpc_transmit_complete it83xx_tx_data(
@@ -423,11 +424,11 @@ static int it83xx_tcpm_set_rx_enable(int port, int enable)
 
 static int it83xx_tcpm_get_message(int port, uint32_t *payload, int *head)
 {
-	it83xx_rx_data(port, head, payload);
+	int ret = it83xx_rx_data(port, head, payload);
 	/* un-mask RX done interrupt */
 	IT83XX_USBPD_IMR(port) &= ~USBPD_REG_MASK_MSG_RX_DONE;
 
-	return EC_SUCCESS;
+	return ret;
 }
 
 static int it83xx_tcpm_transmit(int port,
diff --git a/driver/tcpm/tcpci.c b/driver/tcpm/tcpci.c
index 68453706c7..a2e196351f 100644
--- a/driver/tcpm/tcpci.c
+++ b/driver/tcpm/tcpci.c
@@ -201,7 +201,6 @@ int tcpci_tcpm_get_message(int port, uint32_t *payload, int *head)
 
 	/* RX_BYTE_CNT includes 3 bytes for frame type and header */
 	if (rv != EC_SUCCESS || cnt < 3) {
-		*head = 0;
 		rv = EC_ERROR_UNKNOWN;
 		goto clear;
 	}