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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 C0B55C432C3 for ; Sun, 24 Nov 2019 22:43:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6C851207DD for ; Sun, 24 Nov 2019 22:43:30 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=lunn.ch header.i=@lunn.ch header.b="WzcNPQr9" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726984AbfKXWn3 (ORCPT ); Sun, 24 Nov 2019 17:43:29 -0500 Received: from vps0.lunn.ch ([185.16.172.187]:54512 "EHLO vps0.lunn.ch" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726855AbfKXWn3 (ORCPT ); Sun, 24 Nov 2019 17:43:29 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lunn.ch; s=20171124; h=In-Reply-To:Content-Type:MIME-Version:References:Message-ID: Subject:Cc:To:From:Date:Sender:Reply-To:Content-Transfer-Encoding:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=A8kwyHEGiVOkYsRdP6Ypx4eZ4P3YO4AbBmVTN2SauVA=; b=WzcNPQr9kvOxudKKBwoTFS59cf SLwUe0Rr+84mghQM1JzgF/XxcgrOMlarxLpzlKMV7cH6Fj1n+LZwYiNidyQopL+jJX6NREf11VOLZ kvkR0uIEM9l69Gy9LFsmRyt2iRdlE4HuerEpwkc2Frrfx5OmbHEZaEhsEnIM51/KJaR4=; Received: from andrew by vps0.lunn.ch with local (Exim 4.92.2) (envelope-from ) id 1iZ0bB-0005DR-CI; Sun, 24 Nov 2019 23:43:21 +0100 Date: Sun, 24 Nov 2019 23:43:21 +0100 From: Andrew Lunn To: Vladimir Oltean Cc: Florian Fainelli , Vivien Didelot , "David S. Miller" , Jakub Kicinski , netdev Subject: Re: [PATCH net-next 1/3] net: dsa: Configure the MTU for switch ports Message-ID: <20191124224321.GC6009@lunn.ch> References: <20191123194844.9508-1-olteanv@gmail.com> <20191123194844.9508-2-olteanv@gmail.com> <329f394b-9e6c-d3b0-dc3d-5e3707fa8dd7@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org > Correct. I was actually held back a bit while looking at Andrew's > patch dc0fe7d47f9f ("net: dsa: Set the master device's MTU to account > for DSA overheads") where he basically discarded errors, so that's the > approach I took too (thinking that some DSA masters would not have ops > for changing or reporting the MTU). Ignoring errors is deliberate because some master interfaces just worked without having to set the MTU. I was worried that some that just worked did not implement MTU changes, so i could not error out. And my experience when things did not work was mostly the MTU did not matter, but MRU did. The MAC would send frames with a header, but not receive them with the header. Setting the MTU actually seems to set the MRU on most MACs. But when you are thinking about jumbo frames, i would not ignore the error. We do need to be sure the master interface can support jumbo, and big enough jumbo to support the header. Andrew