linux-kernel - Re: [PATCH] USB: ftdi_sio: Remove tty->low

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Date:	Sat, 3 Oct 2009 14:09:02 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	ebiederm@...ssion.com (Eric W. Biederman)
Cc:	Johan Hovold <jhovold@...il.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Michael Trimarchi <trimarchi@...dalf.sssup.it>,
	Oliver Neukum <oliver@...kum.org>, linux-usb@...r.kernel.org,
	Alan Cox <alan@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] USB: ftdi_sio: Remove tty->low_latency.

On Fri, 02 Oct 2009 16:00:41 -0700
ebiederm@...ssion.com (Eric W. Biederman) wrote:

> 
> 
> I have seen a hang in:
>   /bin/stty (changing the baud rate)
>     set_termios
>       tty_wait_until_sent
>         tty_chars_in_buffer
>           ftdi_chars_in_buffer
> 
> Where the driver wedged for a serial port and no progress
> was made.
> 
> This happened to me several times with 2.6.31.  My initial
> hypothesis was this was a hardware error (as it only happened
> on single piece of hardware).  With all of the driver problems
> I suspect it could be a driver bug.

Driver bug I would think - or setup. If you've genuinely got the port
flow controlled then a request to set the termios after the I/O will wait
until a signal or carrier change (or indeed forever) quite correctly.
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