From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 44110C433F5 for ; Fri, 25 Feb 2022 10:33:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239545AbiBYKdk (ORCPT ); Fri, 25 Feb 2022 05:33:40 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54688 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239496AbiBYKdc (ORCPT ); Fri, 25 Feb 2022 05:33:32 -0500 Received: from 1wt.eu (wtarreau.pck.nerim.net [62.212.114.60]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id C7E76197B7F for ; Fri, 25 Feb 2022 02:32:59 -0800 (PST) Received: (from willy@localhost) by pcw.home.local (8.15.2/8.15.2/Submit) id 21PAWd3d018756; Fri, 25 Feb 2022 11:32:39 +0100 Date: Fri, 25 Feb 2022 11:32:39 +0100 From: Willy Tarreau To: David Laight Cc: "'Steven Rostedt'" , LKML , Petr Mladek , Sergey Senozhatsky , John Ogness Subject: Re: Strange output on the console Message-ID: <20220225103239.GA18720@1wt.eu> References: <20220224230035.36547137@gandalf.local.home> <61226fc12ff9459d8daed8e346d6ab94@AcuMS.aculab.com> <20220225063637.GA18039@1wt.eu> <1dcb185901f04a5ea2476a449e371167@AcuMS.aculab.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1dcb185901f04a5ea2476a449e371167@AcuMS.aculab.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 25, 2022 at 10:11:43AM +0000, David Laight wrote: > From: Willy Tarreau > > Sent: 25 February 2022 06:37 > > > > On Fri, Feb 25, 2022 at 06:12:35AM +0000, David Laight wrote: > > > From: Steven Rostedt > > > > Sent: 25 February 2022 04:01 > > > > > > > > I've been noticing that my tests have been spitting out strange output on > > > > the console. It would happen at boot up and then clear up. It looks like > > > > something screwed up with the serial timing. > > > > > > > > Attached is a dmesg of one of my test runs as an example. > > > > > > > > I've noticed this on both 32 bit and 64 bit x86. > > > > > > > > I haven't had time to look deeper into this, but I figured I let you know > > > > about it. > > > > > > > > And it always seems to happen right after: > > > > > > > > Serial: 8250/16550 driver, 4 ports, IRQ sharing enabled > > > > > > > > Maybe this is a serial issue and not a printk one? :-/ > > > > > > Looks very much like the serial baud rate is being reset. > > > > I don't think it's the baud rate, characters are still readable, it > > looks more like a fifo being too short and causing lots of chars to > > be dropped. > > Just before it recovers there is this output: > ATaitoscic nitahi tuPiet mfba Ae: aD nCt AH0 nP0 > That is probably 'fifo not enabled'. > > But the earlier output doesn't have many different characters in it. > Which is typical of the baud rate being wrong. I don't think so, here's the beginning of the capture: Serial: 8250/16550 driver, 4 ports, IRQ sharing enabled 0SI 15Nto LgtAsri[dnei00ieC nm i:0eom:Soce [ad000Ade s:ii SSLtbueludAis002h00 1)ASrPn Ars004h00 7ARrPn All of these chars are within the printable set, so there's a probability of ~37% per char, so even for a short string of 9 chars like the first line, that's a 0.01% chance of it respecting the set. That's why for me it definitely doesn't correspond to a baud rate issue. With wrong baud rates you get lots of garbage in the full 8-bit range. In addition there are even upper case at the beginning of the lines which probably correspond to the ones that are printed on these lines. Willy