linux-kernel - [PATCH 1/2] serial: core: Introduce callback for start_rx and do stop_rx in suspend only if this callback implementation is present.

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Date:   Wed,  8 Jun 2022 00:22:44 +0530
From:   Vijaya Krishna Nivarthi <quic_vnivarth@...cinc.com>
To:     agross@...nel.org, bjorn.andersson@...aro.org,
        gregkh@...uxfoundation.org, jirislaby@...nel.org,
        linux-arm-msm@...r.kernel.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: [PATCH 1/2] serial: core: Introduce callback for start_rx and do stop_rx in suspend only if this callback implementation is present.

In suspend sequence there is a need to perform stop_rx during suspend
sequence to prevent any asynchronous data over rx line. However this
can cause problem to drivers which dont do re-start_rx during set_termios.

Add new callback start_rx and perform stop_rx only when implementation of
start_rx is present. Also add call to start_rx in resume sequence so that
drivers who come across this problem can make use of this framework.

Fixes: c9d2325cdb92 ("serial: core: Do stop_rx in suspend path for console if console_suspend is disabled")
Signed-off-by: Vijaya Krishna Nivarthi <quic_vnivarth@...cinc.com>
---
 drivers/tty/serial/serial_core.c | 9 ++++++---
 include/linux/serial_core.h      | 1 +
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 9a85b41..338ebad 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -2214,11 +2214,12 @@ int uart_suspend_port(struct uart_driver *drv, struct uart_port *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
+	 * over RX line. However ensure that we will be
+	 * able to Re-start_rx later.
 	 */
 	if (!console_suspend_enabled && uart_console(uport)) {
-		uport->ops->stop_rx(uport);
+		if (uport->ops->start_rx)
+			uport->ops->stop_rx(uport);
 		goto unlock;
 	}
 
@@ -2310,6 +2311,8 @@ int uart_resume_port(struct uart_driver *drv, struct uart_port *uport)
 		if (console_suspend_enabled)
 			uart_change_pm(state, UART_PM_STATE_ON);
 		uport->ops->set_termios(uport, &termios, NULL);
+		if (!console_suspend_enabled && uport->ops->start_rx)
+			uport->ops->start_rx(uport);
 		if (console_suspend_enabled)
 			console_start(uport->cons);
 	}
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index cbd5070..657a0fc 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -45,6 +45,7 @@ struct uart_ops {
 	void		(*unthrottle)(struct uart_port *);
 	void		(*send_xchar)(struct uart_port *, char ch);
 	void		(*stop_rx)(struct uart_port *);
+	void		(*start_rx)(struct uart_port *);
 	void		(*enable_ms)(struct uart_port *);
 	void		(*break_ctl)(struct uart_port *, int ctl);
 	int		(*startup)(struct uart_port *);
-- 
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