linux-kernel - Re: [PATCH v3] serial: imx: Introduce timeout when waiting on transmitter empty

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Message-ID: <87sez060el.fsf@geanix.com>
Date: Thu, 02 May 2024 11:14:26 +0200
From: Esben Haabendal <esben@...nix.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Marc Kleine-Budde <mkl@...gutronix.de>, Sergey Organov
 <sorganov@...il.com>,  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>,  linux-kernel@...r.kernel.org,
  linux-serial@...r.kernel.org,  imx@...ts.linux.dev,
  linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3] serial: imx: Introduce timeout when waiting on
 transmitter empty

Esben Haabendal <esben@...nix.com> writes:

> 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@...nix.com>
> Acked-by: Marc Kleine-Budde <mkl@...gutronix.de>
> ---
>
> 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

Anything more needed in order to get this merged?

/Esben

>
>  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)