linux-kernel - Re: [PATCH 14/33] serial: 8250: extract serial8250_set_TRG

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Message-ID: <10916f86-b010-8dbf-9100-5f8198c1f37b@linux.intel.com>
Date: Wed, 11 Jun 2025 15:07:53 +0300 (EEST)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: "Jiri Slaby (SUSE)" <jirislaby@...nel.org>
cc: gregkh@...uxfoundation.org, linux-serial@...r.kernel.org, 
    linux-kernel@...r.kernel.org
Subject: Re: [PATCH 14/33] serial: 8250: extract
 serial8250_set_TRG_levels()

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

> serial8250_do_startup() contains peculiar trigger levels setup for
> special ports (16850, ALTR_16550_*). Move this away to a separate
> function: serial8250_set_TRG_levels().
> 
> And use switch-case instead of 'if's.

At this point of series I was already expecting this will come. :-)
Another nice cleanup.

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

-- 
 i.

> Signed-off-by: Jiri Slaby (SUSE) <jirislaby@...nel.org>
> ---
>  drivers/tty/serial/8250/8250_port.c | 77 +++++++++++++++--------------
>  1 file changed, 41 insertions(+), 36 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index 21ff56a31b56..c09a90b38d8f 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -2159,6 +2159,46 @@ static void serial8250_startup_special(struct uart_port *port)
>  	}
>  }
>  
> +static void serial8250_set_TRG_levels(struct uart_port *port)
> +{
> +	struct uart_8250_port *up = up_to_u8250p(port);
> +
> +	switch (port->type) {
> +	/* For a XR16C850, we need to set the trigger levels */
> +	case PORT_16850: {
> +		u8 fctr;
> +
> +		serial_out(up, UART_LCR, UART_LCR_CONF_MODE_B);
> +
> +		fctr = serial_in(up, UART_FCTR) & ~(UART_FCTR_RX|UART_FCTR_TX);
> +		fctr |= UART_FCTR_TRGD;
> +		serial_port_out(port, UART_FCTR, fctr | UART_FCTR_RX);
> +		serial_port_out(port, UART_TRG, UART_TRG_96);
> +		serial_port_out(port, UART_FCTR, fctr | UART_FCTR_TX);
> +		serial_port_out(port, UART_TRG, UART_TRG_96);
> +
> +		serial_port_out(port, UART_LCR, 0);
> +		break;
> +	}
> +	/* For the Altera 16550 variants, set TX threshold trigger level. */
> +	case PORT_ALTR_16550_F32:
> +	case PORT_ALTR_16550_F64:
> +	case PORT_ALTR_16550_F128:
> +		if (port->fifosize <= 1)
> +			return;
> +
> +		/* Bounds checking of TX threshold (valid 0 to fifosize-2) */
> +		if (up->tx_loadsz < 2 || up->tx_loadsz > port->fifosize) {
> +			dev_err(port->dev, "TX FIFO Threshold errors, skipping\n");
> +			return;
> +		}
> +		serial_port_out(port, UART_ALTR_AFR, UART_ALTR_EN_TXFIFO_LW);
> +		serial_port_out(port, UART_ALTR_TX_LOW, port->fifosize - up->tx_loadsz);
> +		port->handle_irq = serial8250_tx_threshold_handle_irq;
> +		break;
> +	}
> +}
> +
>  int serial8250_do_startup(struct uart_port *port)
>  {
>  	struct uart_8250_port *up = up_to_u8250p(port);
> @@ -2208,42 +2248,7 @@ int serial8250_do_startup(struct uart_port *port)
>  		goto out;
>  	}
>  
> -	/*
> -	 * For a XR16C850, we need to set the trigger levels
> -	 */
> -	if (port->type == PORT_16850) {
> -		unsigned char fctr;
> -
> -		serial_out(up, UART_LCR, UART_LCR_CONF_MODE_B);
> -
> -		fctr = serial_in(up, UART_FCTR) & ~(UART_FCTR_RX|UART_FCTR_TX);
> -		serial_port_out(port, UART_FCTR,
> -				fctr | UART_FCTR_TRGD | UART_FCTR_RX);
> -		serial_port_out(port, UART_TRG, UART_TRG_96);
> -		serial_port_out(port, UART_FCTR,
> -				fctr | UART_FCTR_TRGD | UART_FCTR_TX);
> -		serial_port_out(port, UART_TRG, UART_TRG_96);
> -
> -		serial_port_out(port, UART_LCR, 0);
> -	}
> -
> -	/*
> -	 * For the Altera 16550 variants, set TX threshold trigger level.
> -	 */
> -	if (((port->type == PORT_ALTR_16550_F32) ||
> -	     (port->type == PORT_ALTR_16550_F64) ||
> -	     (port->type == PORT_ALTR_16550_F128)) && (port->fifosize > 1)) {
> -		/* Bounds checking of TX threshold (valid 0 to fifosize-2) */
> -		if ((up->tx_loadsz < 2) || (up->tx_loadsz > port->fifosize)) {
> -			dev_err(port->dev, "TX FIFO Threshold errors, skipping\n");
> -		} else {
> -			serial_port_out(port, UART_ALTR_AFR,
> -					UART_ALTR_EN_TXFIFO_LW);
> -			serial_port_out(port, UART_ALTR_TX_LOW,
> -					port->fifosize - up->tx_loadsz);
> -			port->handle_irq = serial8250_tx_threshold_handle_irq;
> -		}
> -	}
> +	serial8250_set_TRG_levels(port);
>  
>  	/* Check if we need to have shared IRQs */
>  	if (port->irq && (up->port.flags & UPF_SHARE_IRQ))
>