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 X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 36B66C46475 for ; Tue, 23 Oct 2018 07:03:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A0DC320665 for ; Tue, 23 Oct 2018 07:03:19 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A0DC320665 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=sorico.fr Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727710AbeJWPZX (ORCPT ); Tue, 23 Oct 2018 11:25:23 -0400 Received: from mout02.posteo.de ([185.67.36.142]:35437 "EHLO mout02.posteo.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727023AbeJWPZW (ORCPT ); Tue, 23 Oct 2018 11:25:22 -0400 X-Greylist: delayed 426 seconds by postgrey-1.27 at vger.kernel.org; Tue, 23 Oct 2018 11:25:21 EDT Received: from submission (posteo.de [89.146.220.130]) by mout02.posteo.de (Postfix) with ESMTPS id 3F6182400FD for ; Tue, 23 Oct 2018 08:56:10 +0200 (CEST) Received: from customer (localhost [127.0.0.1]) by submission (posteo.de) with ESMTPSA id 42fPLJ1jnsz9rxK; Tue, 23 Oct 2018 08:56:07 +0200 (CEST) Subject: Re: CRC errors between mvneta and macb To: Willy Tarreau , Richard Genoud Cc: linux-kernel@vger.kernel.org, Thomas Petazzoni , Antoine Tenart , Gregory CLEMENT , Yelena Krivosheev , Maxime Chevallier , Nicolas Ferre , netdev@vger.kernel.org, Andrew Lunn References: <20181019154439.GC24045@1wt.eu> <31385a3b-2196-94d0-7f4f-52e37ee07a28@sorico.fr> <20181022163429.GA22826@1wt.eu> From: Richard Genoud Message-ID: Date: Tue, 23 Oct 2018 08:56:07 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.0 MIME-Version: 1.0 In-Reply-To: <20181022163429.GA22826@1wt.eu> Content-Type: text/plain; charset=utf-8 Content-Language: fr Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Le 22/10/2018 à 18:34, Willy Tarreau a écrit : > On Mon, Oct 22, 2018 at 05:15:21PM +0200, Richard Genoud wrote: >> After analyzing the ethernet frame on the Davicom PHY's output (pin >> TX+), I find out that the FCS errors occurs when the ethernet preamble >> is longer than 56bits. (something like 58 or 60 bits) >> >> To say this in another way, instead of having 28 times 1-0 followed by >> the SFD (10101011), I see 29 or 30 times 1-0 followed by the SFD. >> (sometimes 29, sometimes 30) >> >> >> Should a longer preamble be considered as an FCS error ? It seems a >> little harsh since the point of the preamble is to synchronize the frame. > > That indeed seems a bit strange considering that you're not supposed to > know what is before the preamble so it would very well contain random > noise looking a lot like alteranted bits. > >> I don't know what the 802.3 standard says about that. > > Just found it :-) > > https://www.trincoll.edu/Academics/MajorsAndMinors/Engineering/Documents/IEEE%20Standard%20for%20Ethernet.pdf > > Page 132, #7.2.3.2 : > > The DTE is required to supply at least 56 bits of preamble in > order to satisfy system requirements. System components consume > preamble bits in order to perform their functions. The number > of preamble bits sourced ensures an adequate number of bits are > provided to each system component to correctly implement its > function. > > So that totally makes sense since the purpose is to enable signal > detection at the hardware leve, hence the problem definitely is on > the receiver in your case. > > Willy > Great ! Thanks ! I'll check on the Marvell side Richard