tty: n_gsm: Fix SOF skipping

[ Upstream commit 84d6f81c1fb58b56eba81ff0a36cf31946064b40 ]

For at least some modems like the TELIT LE910, skipping SOF makes
transfers blocking indefinitely after a short amount of data
transferred.

Given the small improvement provided by skipping the SOF (just one
byte on about 100 bytes), it seems better to completely remove this
"feature" than make it optional.

Fixes: e1eaea46bb40 ("tty: n_gsm line discipline")
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>
Link: https://lore.kernel.org/r/20200512115323.1447922-3-gregory.clement@bootlin.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 9e9016e..d5efacd 100644 (file)
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -685,7 +685,6 @@ static void gsm_data_kick(struct gsm_mux *gsm)
 {
        struct gsm_msg *msg, *nmsg;
        int len;
-       int skip_sof = 0;
 
        list_for_each_entry_safe(msg, nmsg, &gsm->tx_list, list) {
                if (gsm->constipated && msg->addr)
@@ -707,15 +706,10 @@ static void gsm_data_kick(struct gsm_mux *gsm)
                        print_hex_dump_bytes("gsm_data_kick: ",
                                             DUMP_PREFIX_OFFSET,
                                             gsm->txframe, len);
-
-               if (gsm->output(gsm, gsm->txframe + skip_sof,
-                                               len - skip_sof) < 0)
+               if (gsm->output(gsm, gsm->txframe, len) < 0)
                        break;
                /* FIXME: Can eliminate one SOF in many more cases */
                gsm->tx_bytes -= msg->len;
-               /* For a burst of frames skip the extra SOF within the
-                  burst */
-               skip_sof = 1;
 
                list_del(&msg->list);
                kfree(msg);