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

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Date:	Sat, 03 Oct 2009 16:51:32 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
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.

Alan Cox <alan@...rguk.ukuu.org.uk> writes:

> 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.

Not setup.  Neither hardware flow control or software flow control are
used on that port.

What was truly puzzling is that it was the only one out of about 50 in
essentially the same configuration where I saw the problem.

Eric

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