linux-kernel - [V4] serial: core: Do stop_rx in suspend path for console if console

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Date:   Mon, 16 May 2022 14:50:10 +0530
From:   Vijaya Krishna Nivarthi <quic_vnivarth@...cinc.com>
To:     gregkh@...uxfoundation.org, jirislaby@...nel.org,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     quic_msavaliy@...cinc.com, dianders@...omium.org, mka@...omium.org,
        swboyd@...omium.org,
        Vijaya Krishna Nivarthi <quic_vnivarth@...cinc.com>
Subject: [V4] serial: core: Do stop_rx in suspend path for console if console_suspend is disabled

For the case of console_suspend disabled, if back to back suspend/resume
test is executed, at the end of test, sometimes console would appear to
be frozen not responding to input. This would happen because, during
resume, rx transactions can come in before system is ready, malfunction
of rx happens in turn resulting in console appearing to be stuck.

Do a stop_rx in suspend sequence to prevent this.

Signed-off-by: Vijaya Krishna Nivarthi <quic_vnivarth@...cinc.com>
---
v4: moved the change to serial core to apply for all drivers
v3: swapped the order of conditions to be more human readable
v2: restricted patch to contain only stop_rx in suspend sequence
v1: intial patch contained 2 additional unrelated changes in vicinity
---
 drivers/tty/serial/serial_core.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 82a1770..9a85b41 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -2211,9 +2211,16 @@ int uart_suspend_port(struct uart_driver *drv, struct uart_port *uport)
 	}
 	put_device(tty_dev);
 
-	/* Nothing to do if the console is not suspending */
-	if (!console_suspend_enabled && uart_console(uport))
+	/*
+	 * Nothing to do if the console is not suspending
+	 * except stop_rx to prevent any asynchronous data
+	 * over RX line. Re-start_rx, when required, is
+	 * done by set_termios in resume sequence
+	 */
+	if (!console_suspend_enabled && uart_console(uport)) {
+		uport->ops->stop_rx(uport);
 		goto unlock;
+	}
 
 	uport->suspended = 1;
 
-- 
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