On Wed, 11 Jun 2025, Jiri Slaby (SUSE) wrote:

> serial8250_do_set_termios() consists of many registers and up flags
> settings. Extract all these into separate functions. This time, setting
> of FCR.
> 
> serial8250_do_set_termios() looks sane at this point.
> 
> Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>

Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

-- 
 i.

> ---
>  drivers/tty/serial/8250/8250_port.c | 41 ++++++++++++++++++-----------
>  1 file changed, 26 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index 0f16398cc86f..85b75ff0699e 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -2792,6 +2792,30 @@ static void serial8250_set_efr(struct uart_port *port, struct ktermios *termios)
>  	serial_port_out(port, efr_reg, efr);
>  }
>  
> +static void serial8250_set_fcr(struct uart_port *port, struct ktermios *termios)
> +{
> +	struct uart_8250_port *up = up_to_u8250p(port);
> +	bool is_16750 = port->type == PORT_16750;
> +
> +	if (is_16750)
> +		serial_port_out(port, UART_FCR, up->fcr);
> +
> +	/*
> +	 * LCR DLAB must be reset to enable 64-byte FIFO mode. If the FCR is written without DLAB
> +	 * set, this mode will be disabled.
> +	 */
> +	serial_port_out(port, UART_LCR, up->lcr);
> +
> +	if (is_16750)
> +		return;
> +
> +	/* emulated UARTs (Lucent Venus 167x) need two steps */
> +	if (up->fcr & UART_FCR_ENABLE_FIFO)
> +		serial_port_out(port, UART_FCR, UART_FCR_ENABLE_FIFO);
> +
> +	serial_port_out(port, UART_FCR, up->fcr);
> +}
> +
>  void
>  serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
>  		          const struct ktermios *old)
> @@ -2823,22 +2847,9 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
>  	serial8250_set_ier(port, termios);
>  	serial8250_set_efr(port, termios);
>  	serial8250_set_divisor(port, baud, quot, frac);
> -
> -	/*
> -	 * LCR DLAB must be set to enable 64-byte FIFO mode. If the FCR
> -	 * is written without DLAB set, this mode will be disabled.
> -	 */
> -	if (port->type == PORT_16750)
> -		serial_port_out(port, UART_FCR, up->fcr);
> -
> -	serial_port_out(port, UART_LCR, up->lcr);	/* reset DLAB */
> -	if (port->type != PORT_16750) {
> -		/* emulated UARTs (Lucent Venus 167x) need two steps */
> -		if (up->fcr & UART_FCR_ENABLE_FIFO)
> -			serial_port_out(port, UART_FCR, UART_FCR_ENABLE_FIFO);
> -		serial_port_out(port, UART_FCR, up->fcr);	/* set fcr */
> -	}
> +	serial8250_set_fcr(port, termios);
>  	serial8250_set_mctrl(port, port->mctrl);
> +
>  	uart_port_unlock_irqrestore(port, flags);
>  	serial8250_rpm_put(up);
>  
>