linux-device-driver-串行8250回送驱动程序代码？

Question

I want to implement a serial loopback driver code in 8250.c found in /drivers/tty/serial/8250.c as found in linux-3.6.1 kernel. I do not want to use the hardware loopback(ie by shorting pin 2(tx) and 3(rx) of the standard serial port), instead I want to modify the 8250.c driver such that, the data from user space will travel from the "serial8250_tx_char" function directly to the "serial8250_rx_char" without going to the hardware, ie I want to receive what is transmitted?

One possible implementation would be to put the transmission circular buffer data into the tty flip buffer, and then push this data up to the tty core so that the user space can receive it? I want to know how to do it in the code. We can search the "rx and tx" functions mentioned above-that is where I am looking, and how will I test this, means by writing on the device file and then immediately receiving the same.

I also have a sample patch, but not sure, whether it will work.

Any help would be appreciated...

Abhijit

Answer 1

`@@ -2112,6 +2116,7 @@ static int serial8250_startup(struct uart_port *port)
                if (is_real_interrupt(up->port.irq))
                        up->port.mctrl |= TIOCM_OUT2;

   + up->port.mctrl |= TIOCM_LOOP;
    serial8250_set_mctrl(&up->port, up->port.mctrl);

    /* Serial over Lan (SoL) hack:

This will set UART to work in internal loop-back mode.`