linux-kernel - Re: [PATCH] serial: imx: allow CRTSCTS with RTS/CTS GPIOs

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Message-ID: <aPEKVBC++mI+lrKA@lizhi-Precision-Tower-5810>
Date: Thu, 16 Oct 2025 11:08:04 -0400
From: Frank Li <Frank.li@....com>
To: Matthias Schiffer <matthias.schiffer@...tq-group.com>
Cc: 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>,
	Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
	linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
	imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
	linux@...tq-group.com
Subject: Re: [PATCH] serial: imx: allow CRTSCTS with RTS/CTS GPIOs

On Thu, Oct 16, 2025 at 01:37:30PM +0200, Matthias Schiffer wrote:
> The CTS GPIO is only evaluated when the CRTSCTS termios flag is enabled;
> it should be possible to enable the flag when only GPIO and no hardware-
> controlled RTS/CTS are available. UCR2_IRTS is kept enabled in this case,
> so the hardware CTS is ignored.
>
> Fixes: 58362d5be352 ("serial: imx: implement handshaking using gpios with the mctrl_gpio helper")
> Signed-off-by: Matthias Schiffer <matthias.schiffer@...tq-group.com>

Reviewed-by: Frank Li <Frank.Li@....com>

> ---
>  drivers/tty/serial/imx.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
> index 500dfc009d03e..4a54a689a0603 100644
> --- a/drivers/tty/serial/imx.c
> +++ b/drivers/tty/serial/imx.c
> @@ -1117,8 +1117,8 @@ static void imx_uart_set_mctrl(struct uart_port *port, unsigned int mctrl)
>  			ucr2 |= UCR2_CTS;
>  			/*
>  			 * UCR2_IRTS is unset if and only if the port is
> -			 * configured for CRTSCTS, so we use inverted UCR2_IRTS
> -			 * to get the state to restore to.
> +			 * configured for hardware-controlled CRTSCTS, so we use
> +			 * inverted UCR2_IRTS to get the state to restore to.
>  			 */
>  			if (!(ucr2 & UCR2_IRTS))
>  				ucr2 |= UCR2_CTSC;
> @@ -1780,7 +1780,7 @@ imx_uart_set_termios(struct uart_port *port, struct ktermios *termios,
>  	if ((termios->c_cflag & CSIZE) == CS8)
>  		ucr2 |= UCR2_WS;
>
> -	if (!sport->have_rtscts)
> +	if (!sport->have_rtscts && !sport->have_rtsgpio)
>  		termios->c_cflag &= ~CRTSCTS;
>
>  	if (port->rs485.flags & SER_RS485_ENABLED) {
> @@ -1794,7 +1794,7 @@ imx_uart_set_termios(struct uart_port *port, struct ktermios *termios,
>  		else
>  			imx_uart_rts_inactive(sport, &ucr2);
>
> -	} else if (termios->c_cflag & CRTSCTS) {
> +	} else if ((termios->c_cflag & CRTSCTS) && sport->have_rtscts) {
>  		/*
>  		 * Only let receiver control RTS output if we were not requested
>  		 * to have RTS inactive (which then should take precedence).
> @@ -1803,7 +1803,7 @@ imx_uart_set_termios(struct uart_port *port, struct ktermios *termios,
>  			ucr2 |= UCR2_CTSC;
>  	}
>
> -	if (termios->c_cflag & CRTSCTS)
> +	if ((termios->c_cflag & CRTSCTS) && sport->have_rtscts)
>  		ucr2 &= ~UCR2_IRTS;
>  	if (termios->c_cflag & CSTOPB)
>  		ucr2 |= UCR2_STPB;
> --
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