linux-kernel - [PATCH v4 1/3] tty: Rework receive flow control char logic

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Date:   Tue, 26 Apr 2022 17:49:33 +0300
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     linux-serial@...r.kernel.org, Greg KH <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org,
        Gilles Buloz <gilles.buloz@...tron.com>,
        Johan Hovold <johan@...nel.org>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Subject: [PATCH v4 1/3] tty: Rework receive flow control char logic

Add a helper to check if the character is a flow control one. This
rework prepares for adding lookahead done check cleanly to
n_tty_receive_char_flow_ctrl() between n_tty_is_char_flow_ctrl() and
the actions taken on the flow control characters.

No functional changes intended.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
---
 drivers/tty/n_tty.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 88af1cdd2fd1..640c9e871044 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -1220,20 +1220,26 @@ n_tty_receive_signal_char(struct tty_struct *tty, int signal, unsigned char c)
 		process_echoes(tty);
 }
 
+static bool n_tty_is_char_flow_ctrl(struct tty_struct *tty, unsigned char c)
+{
+	return c == START_CHAR(tty) || c == STOP_CHAR(tty);
+}
+
 /* Returns true if c is consumed as flow-control character */
 static bool n_tty_receive_char_flow_ctrl(struct tty_struct *tty, unsigned char c)
 {
+	if (!n_tty_is_char_flow_ctrl(tty, c))
+		return false;
+
 	if (c == START_CHAR(tty)) {
 		start_tty(tty);
 		process_echoes(tty);
 		return true;
 	}
-	if (c == STOP_CHAR(tty)) {
-		stop_tty(tty);
-		return true;
-	}
 
-	return false;
+	/* STOP_CHAR */
+	stop_tty(tty);
+	return true;
 }
 
 static void n_tty_receive_char_special(struct tty_struct *tty, unsigned char c)
-- 
2.30.2