linux-kernel - Re: [SOLVED] Serial buffer corruption [was Re: FTDI usb-serial possible bug]

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Date:	Fri, 4 May 2007 15:41:28 +0200
From:	Oliver Neukum <oneukum@...e.de>
To:	"Antonino Ingargiola" <tritemio@...il.com>
Cc:	linux-usb-users@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [SOLVED] Serial buffer corruption [was Re: FTDI usb-serial possible bug]


> > How do you flush the buffers? Simply reading them out?
> 
> Nope. In python I use the flushInput() method of the serial object
> defined by the pyserial library[0]. The method does just this system
> call:
> 
>     termios.tcflush(self.fd, TERMIOS.TCIFLUSH)

		case TCFLSH:
			retval = tty_check_change(tty);
			if (retval)
				return retval;
				
			ld = tty_ldisc_ref(tty);
			switch (arg) {
			case TCIFLUSH:
				if (ld && ld->flush_buffer)
					ld->flush_buffer(tty);
				break;
			case TCIOFLUSH:
				if (ld && ld->flush_buffer)
					ld->flush_buffer(tty);
				/* fall through */
			case TCOFLUSH:
				if (tty->driver->flush_buffer)
					tty->driver->flush_buffer(tty);
				break;
			default:
				tty_ldisc_deref(ld);
				return -EINVAL;
			}
			tty_ldisc_deref(ld);
			return 0;

Most likely you were using n_tty.

static void n_tty_flush_buffer(struct tty_struct * tty)
{
	/* clear everything and unthrottle the driver */
	reset_buffer_flags(tty);
	
	if (!tty->link)
		return;

	if (tty->link->packet) {
		tty->ctrl_status |= TIOCPKT_FLUSHREAD;
		wake_up_interruptible(&tty->link->read_wait);
	}
}

It sets TIOCPKT_FLUSHREAD, which is used nowhere else in the kernel.
And I am confused. Could somebody who has some experience in the
tty layer comment on that?

	Regards
		Oliver
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