[RFC PATCH] ratp: Fix retransmission for header-only packets

[Jules Maselbas]

Using sendmsg_current to detect if a packet needs to be retransmitted is
brittle as only packets containing data will ever be considered, packets
only containing a header (without data) were never being retransmitted.

The sendbuf_len is used to determine if a packets is being send or not,
a non-zero length means that a packets is still being in the "try-send"
state, the length is not set to zero when a valid SN is received.

Retransmission issue can be easily reproduced with a physical UART (not
cdc_acm over USB), by running the following command:

    while ratp-barebox-cli -b 115200 -t /dev/ttyACMx -p; do :; done

Alternatively, it is possible to modify lib/ratp.c to force packets to
be sent by the retransmission logic with the following change:

    @ int ratp_send_pkt(struct ratp_internal *ri, void *pkt, int length)
                    ri->sendbuf_len = length;
    -               ri->retransmission_timer_start = get_time_ns();
    +               ri->retransmission_timer_start = get_time_ns() - ri->rto * MSECOND/2;
                    ri->retransmission_count = 0;
            }
    -       return ri->ratp->send(ri->ratp, pkt, length);
    +       return 0;

Signed-off-by: Jules Maselbas <jmaselbas at kalray.eu>
---
 lib/ratp.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/lib/ratp.c b/lib/ratp.c
index ce30223bac..afa76ac894 100644
--- a/lib/ratp.c
+++ b/lib/ratp.c
@@ -1391,6 +1391,9 @@ static int ratp_state_machine(struct ratp_internal *ri, void *pkt)
 	ratp_print_header(ri, hdr, "                      recv");
 	pr_debug(" state %s\n", ratp_state_str[ri->state]);
 
+	if ((hdr->control & RATP_CONTROL_ACK) && (ratp_an_expected(ri, hdr)))
+		ri->sendbuf_len = 0;
+
 	switch (ri->state) {
 	case RATP_STATE_LISTEN:
 		ratp_behaviour_a(ri, pkt);
@@ -1580,9 +1583,8 @@ int ratp_poll(struct ratp *ratp)
 		}
 	}
 
-	if (ri->sendmsg_current && is_timeout(ri->retransmission_timer_start,
+	if (ri->sendbuf_len && is_timeout(ri->retransmission_timer_start,
 	    ri->rto * MSECOND)) {
-
 		ri->retransmission_count++;
 		if (ri->retransmission_count == ri->max_retransmission) {
 			ri->status = ret = -ETIMEDOUT;
@@ -1601,7 +1603,7 @@ int ratp_poll(struct ratp *ratp)
 			goto out;
 	}
 
-	if (!ri->sendmsg_current && !list_empty(&ri->sendmsg))
+	if (ri->sendbuf_len == 0 && !list_empty(&ri->sendmsg))
 		ratp_send_next_data(ri);
 
 	ret = 0;
-- 
2.17.1