linux-kernel - Re: [PATCH 19/33] serial: 8250: extract serial8250_set_trigger_for_slow

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Message-ID: <ac284b63-2232-639d-b94d-2116cc680173@linux.intel.com>
Date: Wed, 11 Jun 2025 15:34:15 +0300 (EEST)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: "Jiri Slaby (SUSE)" <jirislaby@...nel.org>
cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
    linux-serial <linux-serial@...r.kernel.org>, 
    LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 19/33] serial: 8250: extract
 serial8250_set_trigger_for_slow_speed()

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 trigger level for slow speeds.
> 
> Signed-off-by: Jiri Slaby (SUSE) <jirislaby@...nel.org>
> ---
>  drivers/tty/serial/8250/8250_port.c | 26 +++++++++++++++++++-------
>  1 file changed, 19 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index edfbaa6b7a1b..52385314c426 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -2686,6 +2686,24 @@ static void serial8250_set_mini(struct uart_port *port, struct ktermios *termios
>  	}
>  }
>  
> +static void serial8250_set_trigger_for_slow_speed(struct uart_port *port, struct ktermios *termios,
> +						  unsigned int baud)
> +{
> +	struct uart_8250_port *up = up_to_u8250p(port);
> +
> +	if (!(up->capabilities & UART_CAP_FIFO))
> +		return;
> +	if (port->fifosize <= 1)
> +		return;
> +	if (baud >= 2400)
> +		return;
> +	if (up->dma)

Nit, I'd have put the DMA check before the speed check.

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

> +		return;
> +
> +	up->fcr &= ~UART_FCR_TRIGGER_MASK;
> +	up->fcr |= UART_FCR_TRIGGER_1;
> +}
> +
>  void
>  serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
>  		          const struct ktermios *old)
> @@ -2710,13 +2728,7 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
>  	uart_port_lock_irqsave(port, &flags);
>  
>  	up->lcr = cval;					/* Save computed LCR */
> -
> -	if (up->capabilities & UART_CAP_FIFO && port->fifosize > 1) {
> -		if (baud < 2400 && !up->dma) {
> -			up->fcr &= ~UART_FCR_TRIGGER_MASK;
> -			up->fcr |= UART_FCR_TRIGGER_1;
> -		}
> -	}
> +	serial8250_set_trigger_for_slow_speed(port, termios, baud);
>  
>  	/*
>  	 * MCR-based auto flow control.  When AFE is enabled, RTS will be
> 

-- 
 i.