Re: [PATCH v2 2/5] serial: 8250: extract serial8250_iir_txen_test()

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

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On Tue, 24 Jun 2025, Jiri Slaby (SUSE) wrote:

> After commit 795158691cc0 ("serial: 8250: extract
> serial8250_initialize()"), split serial8250_initialize() even more --
> the TX enable test part of this code can be separated into
> serial8250_iir_txen_test().
> 
> Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
> Suggested-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
> ---
>  drivers/tty/serial/8250/8250_port.c | 49 ++++++++++++++++-------------
>  1 file changed, 28 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index 0f85a2f292fc..5bb0ca04da55 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -2230,16 +2230,19 @@ static void serial8250_init_mctrl(struct uart_port *port)
>  	serial8250_set_mctrl(port, port->mctrl);
>  }
>  
> -static void serial8250_initialize(struct uart_port *port)
> +static void serial8250_iir_txen_test(struct uart_port *port)
>  {
>  	struct uart_8250_port *up = up_to_u8250p(port);
> -	unsigned long flags;
>  	bool lsr_TEMT, iir_NOINT;
>  
> -	serial_port_out(port, UART_LCR, UART_LCR_WLEN8);
> +	if (port->quirks & UPQ_NO_TXEN_TEST)
> +		return;
>  
> -	uart_port_lock_irqsave(port, &flags);
> -	serial8250_init_mctrl(port);
> +	/* Do a quick test to see if we receive an interrupt when we enable the TX irq. */
> +	serial_port_out(port, UART_IER, UART_IER_THRI);
> +	lsr_TEMT = serial_port_in(port, UART_LSR) & UART_LSR_TEMT;
> +	iir_NOINT = serial_port_in(port, UART_IIR) & UART_IIR_NO_INT;
> +	serial_port_out(port, UART_IER, 0);
>  
>  	/*
>  	 * Serial over Lan (SoL) hack:
> @@ -2247,26 +2250,30 @@ static void serial8250_initialize(struct uart_port *port)
>  	 * Lan.  Those chips take a longer time than a normal serial device to signalize that a
>  	 * transmission data was queued. Due to that, the above test generally fails. One solution
>  	 * would be to delay the reading of iir. However, this is not reliable, since the timeout is
> -	 * variable. So, let's just don't test if we receive TX irq.  This way, we'll never enable
> -	 * UART_BUG_TXEN.
> +	 * variable. So, in case of UPQ_NO_TXEN_TEST, let's just don't test if we receive TX irq.
> +	 * This way, we'll never enable UART_BUG_TXEN.
>  	 */
> -	if (!(port->quirks & UPQ_NO_TXEN_TEST)) {
> -		/* Do a quick test to see if we receive an interrupt when we enable the TX irq. */
> -		serial_port_out(port, UART_IER, UART_IER_THRI);
> -		lsr_TEMT = serial_port_in(port, UART_LSR) & UART_LSR_TEMT;
> -		iir_NOINT = serial_port_in(port, UART_IIR) & UART_IIR_NO_INT;
> -		serial_port_out(port, UART_IER, 0);
> -
> -		if (lsr_TEMT && iir_NOINT) {
> -			if (!(up->bugs & UART_BUG_TXEN)) {
> -				up->bugs |= UART_BUG_TXEN;
> -				dev_dbg(port->dev, "enabling bad tx status workarounds\n");
> -			}
> -		} else {
> -			up->bugs &= ~UART_BUG_TXEN;
> +	if (lsr_TEMT && iir_NOINT) {
> +		if (!(up->bugs & UART_BUG_TXEN)) {
> +			up->bugs |= UART_BUG_TXEN;
> +			dev_dbg(port->dev, "enabling bad tx status workarounds\n");
>  		}
> +		return;
>  	}
>  
> +	/* FIXME: why is this needed? */
> +	up->bugs &= ~UART_BUG_TXEN;
> +}
> +
> +static void serial8250_initialize(struct uart_port *port)
> +{
> +	unsigned long flags;
> +
> +	serial_port_out(port, UART_LCR, UART_LCR_WLEN8);
> +
> +	uart_port_lock_irqsave(port, &flags);
> +	serial8250_init_mctrl(port);
> +	serial8250_iir_txen_test(port);
>  	uart_port_unlock_irqrestore(port, flags);
>  }
>  
> 

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

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