Re: [patch] serial: add parameter to force skipping the test for the TXEN bug

[Andrew Morton <akpm@linux-foundation.org>]

On Mon, 20 Apr 2009 18:05:49 -0400
Chuck Ebbert <cebbert@redhat.com> wrote:

> serial: add parameter to force skipping the test for the TXEN bug
> 
> Allow users to force skipping the TXEN test at init time. Applies
> to all serial ports. Intended for debugging only.
> 

<scratches head @ changelog>

> 
> Index: linux-2.6.29.noarch/drivers/serial/8250.c
> ===================================================================
> --- linux-2.6.29.noarch.orig/drivers/serial/8250.c
> +++ linux-2.6.29.noarch/drivers/serial/8250.c
> @@ -67,6 +67,8 @@ static int serial_index(struct uart_port
>  	return (serial8250_reg.minor - 64) + port->line;
>  }
>  
> +static unsigned int skip_txen_test; /* force skip of txen test at init time */
> +
>  /*
>   * Debugging.
>   */
> @@ -2097,7 +2099,7 @@ static int serial8250_startup(struct uar
>  	   is variable. So, let's just don't test if we receive
>  	   TX irq. This way, we'll never enable UART_BUG_TXEN.
>  	 */
> -	if (up->port.flags & UPF_NO_TXEN_TEST)
> +	if (skip_txen_test || up->port.flags & UPF_NO_TXEN_TEST)
>  		goto dont_test_tx_en;
>  
>  	/*
> @@ -3245,6 +3247,9 @@ MODULE_PARM_DESC(share_irqs, "Share IRQs
>  module_param(nr_uarts, uint, 0644);
>  MODULE_PARM_DESC(nr_uarts, "Maximum number of UARTs supported. (1-" __MODULE_STRING(CONFIG_SERIAL_8250_NR_UARTS) ")");
>  
> +module_param(skip_txen_test, uint, 0644);
> +MODULE_PARM_DESC(skip_txen_test, "Skip checking for the TXEN bug at init time");
> +
>  #ifdef CONFIG_SERIAL_8250_RSA
>  module_param_array(probe_rsa, ulong, &probe_rsa_count, 0444);
>  MODULE_PARM_DESC(probe_rsa, "Probe I/O ports for RSA");

Why is this useful?  What is the problem which you're solving here?