linux-kernel - [PATCH 1/2] serial: imx: Introduce timeout when waiting on transmitter empty

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Date: Fri,  5 Apr 2024 11:25:13 +0200
From: Esben Haabendal <esben@...nix.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jirislaby@...nel.org>,
	Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>
Cc: Marc Kleine-Budde <mkl@...gutronix.de>,
	linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org,
	imx@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org
Subject: [PATCH 1/2] serial: imx: Introduce timeout when waiting on transmitter empty

By waiting at most 1 second for USR2_TXDC to be set, we avoid a potentital
deadlock.

In case of the timeout, there is not much we can do, so we simply ignore
the transmitter state and optimistically try to continue.

Signed-off-by: Esben Haabendal <esben@...nix.com>
Acked-by: Marc Kleine-Budde <mkl@...gutronix.de>
---
 drivers/tty/serial/imx.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index e14813250616..09c1678ddfd4 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -26,6 +26,7 @@
 #include <linux/slab.h>
 #include <linux/of.h>
 #include <linux/io.h>
+#include <linux/iopoll.h>
 #include <linux/dma-mapping.h>
 
 #include <asm/irq.h>
@@ -2010,7 +2011,7 @@ imx_uart_console_write(struct console *co, const char *s, unsigned int count)
 	struct imx_port *sport = imx_uart_ports[co->index];
 	struct imx_port_ucrs old_ucr;
 	unsigned long flags;
-	unsigned int ucr1;
+	unsigned int ucr1, usr2;
 	int locked = 1;
 
 	if (sport->port.sysrq)
@@ -2041,8 +2042,8 @@ imx_uart_console_write(struct console *co, const char *s, unsigned int count)
 	 *	Finally, wait for transmitter to become empty
 	 *	and restore UCR1/2/3
 	 */
-	while (!(imx_uart_readl(sport, USR2) & USR2_TXDC));
-
+	read_poll_timeout_atomic(imx_uart_readl, usr2, usr2 & USR2_TXDC,
+				 0, USEC_PER_SEC, false, sport, USR2);
 	imx_uart_ucrs_restore(sport, &old_ucr);
 
 	if (locked)
-- 
2.44.0