tty: n_gsm: Fix SOF skipping

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>

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 67c8f8173023d0490d2b90eb3413c676d92d54f6..d8d196645500b96df46c3003c15a4b0430c78dd6 100644 (file)
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -667,7 +667,6 @@ 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)
@@ -689,15 +688,10 @@ 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);