1 files changed, 20 insertions, 4 deletions

diff --git a/drivers/platform/surface/aggregator/ssh_packet_layer.c b/drivers/platform/surface/aggregator/ssh_packet_layer.c
index 6748fe4ac5d5..def8d7ac541f 100644
--- a/drivers/platform/surface/aggregator/ssh_packet_layer.c
+++ b/drivers/platform/surface/aggregator/ssh_packet_layer.c
@@ -1596,16 +1596,32 @@ static void ssh_ptl_timeout_reap(struct work_struct *work)
 		ssh_ptl_tx_wakeup_packet(ptl);
 }
 
-static bool ssh_ptl_rx_retransmit_check(struct ssh_ptl *ptl, u8 seq)
+static bool ssh_ptl_rx_retransmit_check(struct ssh_ptl *ptl, const struct ssh_frame *frame)
 {
 	int i;
 
 	/*
+	 * Ignore unsequenced packets. On some devices (notably Surface Pro 9),
+	 * unsequenced events will always be sent with SEQ=0x00. Attempting to
+	 * detect retransmission would thus just block all events.
+	 *
+	 * While sequence numbers would also allow detection of retransmitted
+	 * packets in unsequenced communication, they have only ever been used
+	 * to cover edge-cases in sequenced transmission. In particular, the
+	 * only instance of packets being retransmitted (that we are aware of)
+	 * is due to an ACK timeout. As this does not happen in unsequenced
+	 * communication, skip the retransmission check for those packets
+	 * entirely.
+	 */
+	if (frame->type == SSH_FRAME_TYPE_DATA_NSQ)
+		return false;
+
+	/*
 	 * Check if SEQ has been seen recently (i.e. packet was
 	 * re-transmitted and we should ignore it).
 	 */
 	for (i = 0; i < ARRAY_SIZE(ptl->rx.blocked.seqs); i++) {
-		if (likely(ptl->rx.blocked.seqs[i] != seq))
+		if (likely(ptl->rx.blocked.seqs[i] != frame->seq))
 			continue;
 
 		ptl_dbg(ptl, "ptl: ignoring repeated data packet\n");
@@ -1613,7 +1629,7 @@ static bool ssh_ptl_rx_retransmit_check(struct ssh_ptl *ptl, u8 seq)
 	}
 
 	/* Update list of blocked sequence IDs. */
-	ptl->rx.blocked.seqs[ptl->rx.blocked.offset] = seq;
+	ptl->rx.blocked.seqs[ptl->rx.blocked.offset] = frame->seq;
 	ptl->rx.blocked.offset = (ptl->rx.blocked.offset + 1)
 				  % ARRAY_SIZE(ptl->rx.blocked.seqs);
 
@@ -1624,7 +1640,7 @@ static void ssh_ptl_rx_dataframe(struct ssh_ptl *ptl,
 				 const struct ssh_frame *frame,
 				 const struct ssam_span *payload)
 {
-	if (ssh_ptl_rx_retransmit_check(ptl, frame->seq))
+	if (ssh_ptl_rx_retransmit_check(ptl, frame))
 		return;
 
 	ptl->ops.data_received(ptl, payload);