linux-kernel - [PATCH 5.4 141/314] tty: n

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Message-Id: <20200623195345.586398247@linuxfoundation.org>
Date:   Tue, 23 Jun 2020 21:55:36 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Gregory CLEMENT <gregory.clement@...tlin.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.4 141/314] tty: n_gsm: Fix SOF skipping

From: Gregory CLEMENT <gregory.clement@...tlin.com>

[ 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@...tlin.com>
Link: https://lore.kernel.org/r/20200512115323.1447922-3-gregory.clement@bootlin.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/tty/n_gsm.c | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 36a3eb4ad4c55..a5165f989fcf6 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -669,7 +669,6 @@ 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)
@@ -691,15 +690,10 @@ 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);
-- 
2.25.1