How to shutdown console redirection

[Peter Teoh]

read this:

http://elinux.org/Disable_Console

and this:

http://elinux.org/Kernel_Debugging_Tips#Controlling_console_output

Perhaps u can extract relevant APIs from below URLs to solve your problem:

a.   at the hardware level, serial communication can come from UART
interface, or infrared interface, or USB.

b.   next, is the 8250.c handler:
http://lxr.free-electrons.com/source/drivers/tty/serial/<http://lxr.free-electrons.com/source/drivers/tty/serial/serial_core.c>8250_*.c
(star represent the different hardware devices handling the serial signals).

c.   next all these information will feed into serial_core.c (USB is not
included here):

http://lxr.free-electrons.com/source/drivers/tty/serial/serial_core.c

And here u can see how u can disable the signal from software standpoint,
eg,

In particular:

 78 <http://lxr.free-electrons.com/source/drivers/tty/serial/serial_core.c#L78>
static void uart_stop
<http://lxr.free-electrons.com/ident?i=uart_stop>(struct tty_struct
<http://lxr.free-electrons.com/ident?i=tty_struct> *tty
<http://lxr.free-electrons.com/ident?i=tty>)
 79 <http://lxr.free-electrons.com/source/drivers/tty/serial/serial_core.c#L79>
{
 80 <http://lxr.free-electrons.com/source/drivers/tty/serial/serial_core.c#L80>
        struct uart_state
<http://lxr.free-electrons.com/ident?i=uart_state> *state
<http://lxr.free-electrons.com/ident?i=state> = tty
<http://lxr.free-electrons.com/ident?i=tty>->driver_data
<http://lxr.free-electrons.com/ident?i=driver_data>;
 81 <http://lxr.free-electrons.com/source/drivers/tty/serial/serial_core.c#L81>
        struct uart_port
<http://lxr.free-electrons.com/ident?i=uart_port> *port
<http://lxr.free-electrons.com/ident?i=port> = state
<http://lxr.free-electrons.com/ident?i=state>->uart_port
<http://lxr.free-electrons.com/ident?i=uart_port>;
 82 <http://lxr.free-electrons.com/source/drivers/tty/serial/serial_core.c#L82>
        unsigned long flags
<http://lxr.free-electrons.com/ident?i=flags>;
 83 <http://lxr.free-electrons.com/source/drivers/tty/serial/serial_core.c#L83>
 84 <http://lxr.free-electrons.com/source/drivers/tty/serial/serial_core.c#L84>
        spin_lock_irqsave
<http://lxr.free-electrons.com/ident?i=spin_lock_irqsave>(&port
<http://lxr.free-electrons.com/ident?i=port>->lock
<http://lxr.free-electrons.com/ident?i=lock>, flags
<http://lxr.free-electrons.com/ident?i=flags>);
 85 <http://lxr.free-electrons.com/source/drivers/tty/serial/serial_core.c#L85>
        port <http://lxr.free-electrons.com/ident?i=port>->ops
<http://lxr.free-electrons.com/ident?i=ops>->stop_tx(port
<http://lxr.free-electrons.com/ident?i=port>);
 86 <http://lxr.free-electrons.com/source/drivers/tty/serial/serial_core.c#L86>
        spin_unlock_irqrestore
<http://lxr.free-electrons.com/ident?i=spin_unlock_irqrestore>(&port
<http://lxr.free-electrons.com/ident?i=port>->lock
<http://lxr.free-electrons.com/ident?i=lock>, flags
<http://lxr.free-electrons.com/ident?i=flags>);
 87 <http://lxr.free-electrons.com/source/drivers/tty/serial/serial_core.c#L87>
}
 88 <http://lxr.free-electrons.com/source/drivers/tty/serial/serial_core.c#L88>

>From above, u can see stop_tx() can be called, looking further into 8250.c:

static void serial8250_stop_tx(struct uart_port *port)
{
        struct uart_8250_port *up =
                container_of(port, struct uart_8250_port, port);

        __stop_tx(up);

        /*
         * We really want to stop the transmitter from sending.
         */
        if (up->port.type == PORT_16C950) {
                up->acr |= UART_ACR_TXDIS;
                serial_icr_write(up, UART_ACR, up->acr);
        }
}

And referring further to definition:

/*
 * The 16C950 Additional Control Register
 */
#define UART_ACR_RXDIS  0x01    /* Receiver disable */
#define UART_ACR_TXDIS  0x02    /* Transmitter disable */

So perhaps writing UART_ACR_XXX_DIS will disable the input/output:

drivers/tty/serial/8250.c:		up->acr |= UART_ACR_TXDIS;

drivers/tty/serial/8250.c: up->acr &= ~UART_ACR_TXDIS;

Experiment first....I am just guessing....


On Wed, Jan 4, 2012 at 8:43 AM, hz hanks <hankshz at gmail.com> wrote:

> Hi, all~
> I'm studying in an embedded Linux board with only one uart, which is
> set default as the console display. Now as I try to develop uart
> driver, I want to shutdown this console redirection temporarily. But I
> don't know how? I search the Internet, but there's only the tutorial
> for setting this redirection rather than shutdown it. Is there anyone
> can help? Thank you very much.
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>



-- 
Regards,
Peter Teoh
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