Problem in writing to the serial port in 2.4.19

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Hello, all.

I wrote a linux loadable kernel module
that exchanges data with a device through /dev/ttyS0.
For this purpose, I set the serial tty's ldisc (tty->ldisc)
to my own line discipline and it worked well in the kernel 2.4.2.

But, when I upgrade the kernel to 2.4.19,
it does not seem to send data as it was before.
If I load the module and send some data in succession,
the device attached to the serial port becomes down shortly after.

The following is my routine to send data to /dev/ttyS0:

--
while (len > 0) {
        int space, n_wr;
        if (tty->driver.write_room)
                space = tty->driver.write_room(tty);
        n_wr = (len < space)? len: space;
        if (tty->driver.flush_chars)
                tty->driver.flush_chars(tty);
        n_wr = tty->driver.write(tty, 0, buf, n_wr);
        buf += n_wr;
        len += n_wr;
}
--
In order to send data in succession, I call the above routine
within another while loop with different (buf, len) parameters. 
The scheme worked well in 2.4.2, but does not work in 2.4.19.
So, I re-wrote the routine like this:
--
tty->flags |= (1 << TTY_DO_WRITE_WAKEUP);
while (len > 0) {
        int space, n_wr;
        if (tty->driver.write_room)
                space = tty->driver.write_room(tty);
        n_wr = (len < space)? len: space;
        if (tty->driver.flush_chars)
                tty->driver.flush_chars(tty);
        n_wr = tty->driver.write(tty, 0, buf, n_wr);
        buf += n_wr;
        len += n_wr;
}
--
And, in the function void xx_write_wakeup (struct tty_struct *tty):
--
tty->flags &= ~(1 << TTY_DO_WRITE_WAKEUP);
/* and, re-send data */
--
The result is that both do not work. :-(
I believe the serial driver in 2.4.19 will work correctly.
If there is anything that I'm missing, please let me know.
Thank you in advance.
Joosun.
ps. UART(16550A), baudrate(115200), crtscts(ON).
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• Next message: Alan Cox: "Re: [PATCH] fixes for building kernel using Intel compiler"
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