From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754000Ab2ACQAw (ORCPT ); Tue, 3 Jan 2012 11:00:52 -0500 Received: from mail-ww0-f44.google.com ([74.125.82.44]:64705 "EHLO mail-ww0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753930Ab2ACQAt (ORCPT ); Tue, 3 Jan 2012 11:00:49 -0500 Message-ID: <4F03262D.8090506@suse.cz> Date: Tue, 03 Jan 2012 17:00:45 +0100 From: Jiri Slaby User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0) Gecko/20111223 Thunderbird/10.0 MIME-Version: 1.0 To: Dave Jones , Linux Kernel Subject: Re: serial ports now asserting DTR and RTS during boot; breaks connected hardware References: <20120103153707.GA12771@redhat.com> In-Reply-To: <20120103153707.GA12771@redhat.com> X-Enigmail-Version: 1.3.4 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/03/2012 04:37 PM, Dave Jones wrote: > Jiri, > We got this report from a user who notes a change in behaviour for > his serial hardware over the last few kernel versions. Hi! I'm busy right now, however just after a quick look, it may be related to: https://lkml.org/lkml/2011/12/6/573 I'll take a look later. > https://bugzilla.redhat.com/show_bug.cgi?id=771010 > > This sounds like it might be related to your DTR/RTS changes back in March 2011 maybe ? What changes do you mean? In serial-core.c? That one is not used by USB serials. Hence this wouldn't occur with FTDI. > > Description of problem: > > > > After upgrade from FC14 to FC16, it was discovered that during kernel boot, the > > DTR and RTS signals of serial devices (both real UART and FTDI USB devices) are > > being asserted from driver load to approx 20 seconds afterward. This causes > > some types of hardware connected to these ports to fail as they expect a > > different sequence or controlled activation of these signals. In particular, > > ham radio equipment that uses these signals to key transmitters is now going > > into uncontrolled transmit for nearly the duration of kernel boot. > > > > > > Steps to Reproduce: > > 1. connect RS232 breakout box to serial port > > 2. boot system > > 3. watch DTR and RTS LEDs light as kernel is booting > > > > Actual results: > > > > LEDs light and stay light for almost entire boot duration indicating that DTR > > and RTS are asserting as the kernel boots. > > > > Expected results: > > > > DTR and RTS should not activate while kernel is booting. They should only > > activate when the port is opened by an application and it has performed a > > termios function to enable these signals. > > > > > > Additional info: > > > > The following code in the ftdi_sio driver is one suspect but this behavior > > happens on 8250 UARTs also so it is systemic now, > > > > ftdi_sio.c, line 2161, > > > > /* Ensure RTS and DTR are raised when baudrate changed from 0 > > */ > > if (!old_termios || (old_termios->c_cflag & CBAUD) == B0) > > set_mctrl(port, TIOCM_DTR | TIOCM_RTS); > > > > regards, -- js suse labs