tcpm: fusb302: Don't mistake meaningful packets for GOOD_CRC

If a partner port sends a packet at approximately the same time as we
send a packet, we may end up with the initial packet followed by the
GOOD_CRC reply in our HW FIFO. Don't automatically discard the first
packet in the FIFO. Instead, discard the packet only if it's a GOOD_CRC
packet. And, modify our get_message function to automatically discard
GOOD_CRC in search of a meaningful packet.

In addition, due to interrupt latency, we can't rely on receiving one
interrupt per incoming packet. If our Rx FIFO is non-empty, assume that
it contains at least one packet.

BUG=chrome-os-partner:60242
BRANCH=gru
TEST=Manual on kevin, attach Apple dongle with no inputs. Attach zinger,
verify we negotiate to ~20V. Repeat 10x and verify negotiation is
successful each time.

Signed-off-by: Shawn Nematbakhsh <shawnn@chromium.org>
Change-Id: I7e4430fc2b7ed44b1aa4b561d72c8e1e964b245a
Reviewed-on: https://chromium-review.googlesource.com/414927
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>
(cherry picked from commit 373f5dfd75e8ea5074d26fc6392eafe83de4f905)
Reviewed-on: https://chromium-review.googlesource.com/419186
Commit-Ready: Shawn N <shawnn@chromium.org>
Tested-by: Shawn N <shawnn@chromium.org>
Reviewed-by: Shawn N <shawnn@chromium.org>

1 files changed, 75 insertions, 41 deletions

diff --git a/driver/tcpm/fusb302.c b/driver/tcpm/fusb302.c
index 3bf20f52d4..9bdde5e591 100644
--- a/driver/tcpm/fusb302.c
+++ b/driver/tcpm/fusb302.c
@@ -17,6 +17,9 @@
 #include "usb_pd_tcpc.h"
 #include "util.h"
 
+#define PACKET_IS_GOOD_CRC(head) (PD_HEADER_TYPE(head) == PD_CTRL_GOOD_CRC && \
+				 PD_HEADER_CNT(head) == 0)
+
 static struct fusb302_chip_state {
 	int cc_polarity;
 	int vconn_enabled;
@@ -27,12 +30,19 @@ static struct fusb302_chip_state {
 	uint8_t mdac_rd;
 } state[CONFIG_USB_PD_PORT_COUNT];
 
-/* bring the FUSB302 out of reset after Hard Reset signaling */
+/*
+ * Bring the FUSB302 out of reset after Hard Reset signaling. This will
+ * automatically flush both the Rx and Tx FIFOs.
+ */
 static void fusb302_pd_reset(int port)
 {
 	tcpc_write(port, TCPC_REG_RESET, TCPC_REG_RESET_PD_RESET);
 }
 
+/*
+ * Flush our Rx FIFO. To prevent packet framing issues, this function should
+ * only be called when Rx is disabled.
+ */
 static void fusb302_flush_rx_fifo(int port)
 {
 	/*
@@ -658,56 +668,84 @@ static int fusb302_tcpm_set_rx_enable(int port, int enable)
 	return 0;
 }
 
+/* Return true if our Rx FIFO is empty */
+static int fusb302_rx_fifo_is_empty(int port)
+{
+	int reg;
+
+	return (!tcpc_read(port, TCPC_REG_STATUS1, &reg)) &&
+	       (reg & TCPC_REG_STATUS1_RX_EMPTY);
+}
+
 static int fusb302_tcpm_get_message(int port, uint32_t *payload, int *head)
 {
 	/*
-	 * this is the buffer that will get the burst-read data
+	 * This is the buffer that will get the burst-read data
 	 * from the fusb302.
 	 *
-	 * it's re-used in a couple different spots, the worst of which
+	 * It's re-used in a couple different spots, the worst of which
 	 * is the PD packet (not header) and CRC.
 	 * maximum size necessary = 28 + 4 = 32
 	 */
 	uint8_t buf[32];
-	int rv = 0;
-	int len;
+	int rv, len;
 
-	/* NOTE: Assuming enough memory has been allocated for payload. */
+	/* If our FIFO is empty then we have no packet */
+	if (fusb302_rx_fifo_is_empty(port))
+		return EC_ERROR_UNKNOWN;
 
-	/*
-	 * PART 1 OF BURST READ: Write in register address.
-	 * Issue a START, no STOP.
-	 */
-	tcpc_lock(port, 1);
-	buf[0] = TCPC_REG_FIFOS;
-	rv |= tcpc_xfer(port, buf, 1, 0, 0, I2C_XFER_START);
+	/* Read until we have a non-GoodCRC packet or an empty FIFO */
+	do {
+		buf[0] = TCPC_REG_FIFOS;
+		tcpc_lock(port, 1);
 
-	/*
-	 * PART 2 OF BURST READ: Read up to the header.
-	 * Issue a repeated START, no STOP.
-	 * only grab three bytes so we can get the header
-	 * and determine how many more bytes we need to read.
-	 */
-	rv |= tcpc_xfer(port, 0, 0, buf, 3, I2C_XFER_START);
+		/*
+		 * PART 1 OF BURST READ: Write in register address.
+		 * Issue a START, no STOP.
+		 */
+		rv = tcpc_xfer(port, buf, 1, 0, 0, I2C_XFER_START);
 
-	/* Grab the header */
-	*head = (buf[1] & 0xFF);
-	*head |= ((buf[2] << 8) & 0xFF00);
+		/*
+		 * PART 2 OF BURST READ: Read up to the header.
+		 * Issue a repeated START, no STOP.
+		 * only grab three bytes so we can get the header
+		 * and determine how many more bytes we need to read.
+		 * TODO: Check token to ensure valid packet.
+		 */
+		rv |= tcpc_xfer(port, 0, 0, buf, 3, I2C_XFER_START);
 
-	/* figure out packet length, subtract header bytes */
-	len = get_num_bytes(*head) - 2;
+		/* Grab the header */
+		*head = (buf[1] & 0xFF);
+		*head |= ((buf[2] << 8) & 0xFF00);
 
-	/*
-	 * PART 3 OF BURST READ: Read everything else.
-	 * No START, but do issue a STOP at the end.
-	 * add 4 to len to read CRC out
-	 */
-	rv |= tcpc_xfer(port, 0, 0, buf, len+4, I2C_XFER_STOP);
+		/* figure out packet length, subtract header bytes */
+		len = get_num_bytes(*head) - 2;
 
-	tcpc_lock(port, 0);
+		/*
+		 * PART 3 OF BURST READ: Read everything else.
+		 * No START, but do issue a STOP at the end.
+		 * add 4 to len to read CRC out
+		 */
+		rv |= tcpc_xfer(port, 0, 0, buf, len+4, I2C_XFER_STOP);
 
-	/* return the data */
-	memcpy(payload, buf, len);
+		tcpc_lock(port, 0);
+	} while (!rv && PACKET_IS_GOOD_CRC(*head) &&
+		 !fusb302_rx_fifo_is_empty(port));
+
+	if (!rv) {
+		/* Discard GoodCRC packets */
+		if (PACKET_IS_GOOD_CRC(*head))
+			rv = EC_ERROR_UNKNOWN;
+		else
+			memcpy(payload, buf, len);
+	}
+
+	/*
+	 * If our FIFO is non-empty then we may have a packet, we may get
+	 * fewer interrupts than packets due to interrupt latency.
+	 */
+	if (!fusb302_rx_fifo_is_empty(port))
+		task_set_event(PD_PORT_TO_TASK_ID(port), PD_EVENT_RX, 0);
 
 	return rv;
 }
@@ -800,8 +838,6 @@ void fusb302_tcpc_alert(int port)
 	int interrupt;
 	int interrupta;
 	int interruptb;
-	int head;
-	uint32_t payload[7];
 
 	/* reading interrupt registers clears them */
 
@@ -826,12 +862,10 @@ void fusb302_tcpc_alert(int port)
 		pd_transmit_complete(port, TCPC_TX_COMPLETE_FAILED);
 	}
 
+	/* GoodCRC was received, our FIFO is now non-empty */
 	if (interrupta & TCPC_REG_INTERRUPTA_TX_SUCCESS) {
-		/*
-		 * Sent packet was acknowledged with a GoodCRC,
-		 * so remove GoodCRC message from FIFO.
-		 */
-		tcpm_get_message(port, payload, &head);
+		task_set_event(PD_PORT_TO_TASK_ID(port),
+				PD_EVENT_RX, 0);
 
 		pd_transmit_complete(port, TCPC_TX_COMPLETE_SUCCESS);
 	}