Re: belkin usb serial converter (mct_u232), break not working

[Paul Fulghum <paulkf@microgate.com>]

On Wed, 2004-10-20 at 18:04, Thomas Stewart wrote:
> porttest.c:
> #include <sys/fcntl.h>
> #include <sys/ioctl.h>
> main(int argc, char ** argv) {
>         int r, fd = open(argv[1], O_RDWR|O_NOCTTY);
>         r=ioctl(fd, TCSBRKP, 20);
>         printf("%d\n", r);
>         close(fd);
> }
> 
> $ ./porttest /dev/ttyS0
> 0
> $ ./porttest /dev/ttyUSB0
> 0

OK, this is a kernel problem with send_break() in tty_io.c

Original:

static int send_break(struct tty_struct *tty, int duration)
{
	set_current_state(TASK_INTERRUPTIBLE);

	tty->driver->break_ctl(tty, -1);
	if (!signal_pending(current))
		schedule_timeout(duration);
	tty->driver->break_ctl(tty, 0);
	if (signal_pending(current))
		return -EINTR;
	return 0;
}

The USB serial driver break_ctl() sends a URB which does
a sleep and wakeup changing the task state back to TASK_RUNNING.
Because of this, schedule_timeout() above gets short circuited
and the break condition is not maintained long enough.

The normal serial driver break_ctl() leaves the task state
as TASK_INTERRUPTIBLE so you get the proper delay.

Thomas: try the patch below and let me know the results.

-- 
Paul Fulghum
paulkf@microgate.com

--- linux-2.6.8/drivers/char/tty_io.c	2004-08-14 00:37:15.000000000 -0500
+++ b/drivers/char/tty_io.c	2004-10-20 21:31:55.000000000 -0500
@@ -1703,11 +1703,11 @@ static int tiocsetd(struct tty_struct *t
 
 static int send_break(struct tty_struct *tty, int duration)
 {
-	set_current_state(TASK_INTERRUPTIBLE);
-
 	tty->driver->break_ctl(tty, -1);
-	if (!signal_pending(current))
+	if (!signal_pending(current)) {
+		set_current_state(TASK_INTERRUPTIBLE);
 		schedule_timeout(duration);
+	}
 	tty->driver->break_ctl(tty, 0);
 	if (signal_pending(current))
 		return -EINTR;