[PATCH v3] serial: imx: Introduce timeout when waiting on transmitter empty

From: Esben Haabendal
Date: Thu Apr 11 2024 - 08:19:47 EST


By waiting at most 1 second for USR2_TXDC to be set, we avoid a potential
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@xxxxxxxxxx>
Acked-by: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx>
---

v2:
- Fixed commit message typo
- Remove reference to patch series it originated from. This is a
stand-alone patch

v3:
- Moved this version information into the correct patch section

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