Re: [PATCH 3/3] serial: 8250_mxpcie: take the line settings from the new termios

[Crescent Hsieh]

On Tue, Aug 18, 2026 at 05:39:18PM +0800, Linmao Li wrote:
> mxpcie8250_set_termios() reads the line settings out of
> port->state->port.tty, which is only set once the port has been opened.
> 
> uart_set_options() builds a termios of its own and calls ->set_termios()
> with no tty behind it, so using such a board as the console
> (console=ttyS<n>) dereferences a NULL tty during console setup, as does
> attaching kgdboc to it and resuming a suspended console from
> uart_resume_port().
> 
> Read the settings from the termios the serial core passes in instead.
> It holds the same values on the normal path - uart_change_line_settings()
> passes &tty->termios - and it is what serial8250_do_set_termios() right
> above already uses.
> 
> Fixes: 55edf8511f47 ("serial: 8250_mxpcie: enable automatic RTS/CTS flow control")
> Signed-off-by: Linmao Li <lilinmao@xxxxxxxxxx>

Hi,

I tested this by configuring kgdboc on a CP-168EL-A. Thanks for the fix.

> ---
>  drivers/tty/serial/8250/8250_mxpcie.c | 19 ++++++++++---------
>  1 file changed, 10 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_mxpcie.c b/drivers/tty/serial/8250/8250_mxpcie.c
> index ddd02d5622ec4..eba59f1724b78 100644
> --- a/drivers/tty/serial/8250/8250_mxpcie.c
> +++ b/drivers/tty/serial/8250/8250_mxpcie.c
> @@ -217,8 +217,7 @@ static void mxpcie8250_set_termios(struct uart_port *port,
>  				   const struct ktermios *old)
>  {
>  	struct uart_8250_port *up = up_to_u8250p(port);
> -	struct tty_struct *tty = port->state->port.tty;
> -	unsigned int cflag = tty->termios.c_cflag;
> +	unsigned int cflag = new->c_cflag;

Nit: Since cflag is used only once, while c_iflag and c_cc are
accessed directly through new below, could we drop the local variable
and use new->c_cflag directly for consistency?

>  	u8 efr, val;
>  
>  	serial8250_do_set_termios(port, new, old);
> @@ -233,18 +232,20 @@ static void mxpcie8250_set_termios(struct uart_port *port,
>  		up->port.status |= (UPSTAT_AUTORTS | UPSTAT_AUTOCTS);
>  	}
>  	/* Set on-chip software flow control character */
> -	serial_out(up, MOXA_PUART_XON1, START_CHAR(tty));
> -	serial_out(up, MOXA_PUART_XON2, START_CHAR(tty));
> -	serial_out(up, MOXA_PUART_XOFF1, STOP_CHAR(tty));
> -	serial_out(up, MOXA_PUART_XOFF2, STOP_CHAR(tty));
> +	serial_out(up, MOXA_PUART_XON1, new->c_cc[VSTART]);
> +	serial_out(up, MOXA_PUART_XON2, new->c_cc[VSTART]);
> +	serial_out(up, MOXA_PUART_XOFF1, new->c_cc[VSTOP]);
> +	serial_out(up, MOXA_PUART_XOFF2, new->c_cc[VSTOP]);
>  
> -	val = I_IXON(tty) ? MOXA_PUART_EFR_RX_FLOW_XON1_XOFF1 : MOXA_PUART_EFR_RX_FLOW_DISABLED;
> +	val = (new->c_iflag & IXON) ? MOXA_PUART_EFR_RX_FLOW_XON1_XOFF1 :
> +				      MOXA_PUART_EFR_RX_FLOW_DISABLED;
>  	FIELD_MODIFY(MOXA_PUART_EFR_RX_FLOW_MASK, &efr, val);
>  
> -	val = I_IXOFF(tty) ? MOXA_PUART_EFR_TX_FLOW_XON1_XOFF1 : MOXA_PUART_EFR_TX_FLOW_DISABLED;
> +	val = (new->c_iflag & IXOFF) ? MOXA_PUART_EFR_TX_FLOW_XON1_XOFF1 :
> +				       MOXA_PUART_EFR_TX_FLOW_DISABLED;
>  	FIELD_MODIFY(MOXA_PUART_EFR_TX_FLOW_MASK, &efr, val);
>  
> -	if (I_IXOFF(tty))
> +	if (new->c_iflag & IXOFF)
>  		up->port.status |= UPSTAT_AUTOXOFF;
>  
>  	serial_out(up, MOXA_PUART_EFR, efr);
> -- 
> 2.25.1
> 

---
Thanks,
Crescent Hsieh