Re: [PATCH v5 04/14] serial: 8250_mxpcie: enable automatic RTS/CTS flow control

[Andy Shevchenko]

On Fri, Jul 31, 2026 at 10:49 AM Crescent Hsieh
<crescentcy.hsieh@xxxxxxxx> wrote:
>
> The MUEx50 UART supports automatic RTS/CTS flow control via the enhanced
> feature register.
>
> Implement a mxpcie-specific set_termios() callback that enables MUEx50
> auto-RTS/auto-CTS when CRTSCTS is requested and disables it otherwise.
> Keep the 8250 port status flags in sync with the hardware configuration.

...

> +static void mxpcie8250_set_termios(struct uart_port *port,
> +                                  struct ktermios *new,
> +                                  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;
> +       u8 efr;
> +
> +       serial8250_do_set_termios(port, new, old);

> +       up->port.status &= ~(UPSTAT_AUTORTS | UPSTAT_AUTOCTS);
> +
> +       efr = serial_in(up, MOXA_PUART_EFR);
> +       efr &= ~(MOXA_PUART_EFR_AUTO_RTS | MOXA_PUART_EFR_AUTO_CTS);
> +
> +       if (cflag & CRTSCTS) {
> +               efr |= (MOXA_PUART_EFR_AUTO_RTS | MOXA_PUART_EFR_AUTO_CTS);
> +               up->port.status |= (UPSTAT_AUTORTS | UPSTAT_AUTOCTS);


Don't you want to use FIELD_MODIFY() at least for efr value? Also
if-else looks better, no?

if (..) {
 FIELD_MODIFY(&efr);
 up->port.status ...
} else {
  ...
}

> +       }
> +       serial_out(up, MOXA_PUART_EFR, efr);
> +}

-- 
With Best Regards,
Andy Shevchenko