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 6A434C433F5 for ; Wed, 8 Dec 2021 14:53:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230237AbhLHO5Z (ORCPT ); Wed, 8 Dec 2021 09:57:25 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47310 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229478AbhLHO5Y (ORCPT ); Wed, 8 Dec 2021 09:57:24 -0500 Received: from mail-ed1-x52d.google.com (mail-ed1-x52d.google.com [IPv6:2a00:1450:4864:20::52d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CB46BC061746; Wed, 8 Dec 2021 06:53:52 -0800 (PST) Received: by mail-ed1-x52d.google.com with SMTP id r11so9092313edd.9; Wed, 08 Dec 2021 06:53:52 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=sTcURiIQ8RnWwJ1LvErUaG9rDDP1ZDMbGbFVTr/q3W8=; b=B1BzV0+ygHi3gibMFqpJqSzi6/lPAuO6BleXaiwaUwpF3f2d3qla5J7EL3Wiy0ZDr3 Nuu4MiZ4OeFcROFWMD/gyeDNsQRaQUAp8zy8FwpmAfom+Tk09NW5X/Hqhi21yVNJD92b zEtNtK16HpxlwVSR2nCI/Jf9prIyMRq56BidyBKwC7VvahCTMsXcaApxUrEfio0goHgE Sk9QpceRv8qnH/1NcigD37ovjAlSsKisI1Sz83khPGK0zAdVwGAxbmFRP8CNDSuJH8W+ GfsWfJE2cdJvLE2pRJxWLGbNK8NaADuojKGpMVBl2EmCvwR4S9lBCGduQwzVW8US1QLU L8Rw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=sTcURiIQ8RnWwJ1LvErUaG9rDDP1ZDMbGbFVTr/q3W8=; b=g3CN+AimTuDtzXE+kcuRFwRmsEa8kdGKc6uHuaFNe3csKqzvFy2V4K9jJFCSpcyX4h m6xVh4ALVbZCLHFqeMl+UO173uZ6z2C10RVA4Tt3hom6nSrtGQ+0HUAgGSS4uS39dZMC dfXVU6VgmZVgNTla2FoUTel/TYUTAfj8RR/+LCUqeHSupDH86dIDlYLXkhQQRc3ufdmE GOOVg+Aa34jQ3LOoQSYqf9HJmmYIEg88FaGz0E1PIbxcXH3WUguz52pvKuq3ecBLN40M zwOijZmz510szNm9m6SRLJXBUIWcINUgwA5FIimJgHWcaV3Gld/q8gFADAdBCrHvhig/ aHvA== X-Gm-Message-State: AOAM533EpTjONp0Bg95bvS6lFbxEHidiHnzt9PiUj70xXuj/fHxcO3FU 3cnMXArjsJJDmFMRS0/jIhM= X-Google-Smtp-Source: ABdhPJxt1VvSgndQf2skuU/RFOIXZd3WIAImB9sf1ag7POEUesUB7b0ENtobFGD6UGy5g4yHVsF68g== X-Received: by 2002:a17:906:58d5:: with SMTP id e21mr8140684ejs.540.1638975223528; Wed, 08 Dec 2021 06:53:43 -0800 (PST) Received: from skbuf ([188.25.173.50]) by smtp.gmail.com with ESMTPSA id i8sm2557243edc.12.2021.12.08.06.53.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 08 Dec 2021 06:53:43 -0800 (PST) Date: Wed, 8 Dec 2021 16:53:41 +0200 From: Vladimir Oltean To: Ansuel Smith Cc: Andrew Lunn , Vivien Didelot , Florian Fainelli , "David S. Miller" , Jakub Kicinski , linux-kernel@vger.kernel.org, netdev@vger.kernel.org Subject: Re: [net-next RFC PATCH v2 0/8] Add support for qca8k mdio rw in Ethernet packet Message-ID: <20211208145341.degqvm23bxc3vo7z@skbuf> References: <20211208034040.14457-1-ansuelsmth@gmail.com> <20211208123222.pcljtugpq5clikhq@skbuf> <61b0c239.1c69fb81.9dfd0.5dc2@mx.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <61b0c239.1c69fb81.9dfd0.5dc2@mx.google.com> Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Wed, Dec 08, 2021 at 03:33:27PM +0100, Ansuel Smith wrote: > > But there are some problems with offering a "master_going_up/master_going_down" > > set of callbacks. Specifically, we could easily hook into the NETDEV_PRE_UP/ > > NETDEV_GOING_DOWN netdev notifiers and transform these into DSA switch > > API calls. The goal would be for the qca8k tagger to mark the > > Ethernet-based register access method as available/unavailable, and in > > the regmap implementation, to use that or the other. DSA would then also > > be responsible for calling "master_going_up" when the switch ports and > > master are sufficiently initialized that traffic should be possible. > > But that first "master_going_up" notification is in fact the most > > problematic one, because we may not receive a NETDEV_PRE_UP event, > > because the DSA master may already be up when we probe our switch tree. > > This would be a bit finicky to get right. We may, for instance, hold > > rtnl_lock for the entirety of dsa_tree_setup_master(). This will block > > potentially concurrent netdevice notifiers handled by dsa_slave_nb. > > And while holding rtnl_lock() and immediately after each dsa_master_setup(), > > we may check whether master->flags & IFF_UP is true, and if it is, > > synthesize a call to ds->ops->master_going_up(). We also need to do the > > reverse in dsa_tree_teardown_master(). > > Should we care about holding the lock for that much time? Will do some > test hoping the IFF_UP is sufficient to make the Ethernet mdio work. I'm certainly not smart enough to optimize things, so I'd rather hold the rtnl_lock for as long as I'm comfortable is enough to avoid races. The reason why we must hold rtnl_lock is because during dsa_master_setup(), the value of netdev_uses_dsa(dp->master) changes from false to true. The idea is that if IFF_UP isn't set right now, no problem, release the lock and we'll catch the NETDEV_UP notifier when that will appear. But we want to (a) replay the master up state if it was already up while it wasn't a DSA master (b) avoid a potential race where the master does go up, we receive that notification, but netdev_uses_dsa() doesn't yet return true for it. The model would be similar to what we have for the NETDEV_GOING_DOWN handler. Please wait for me to finish the sja1105 conversion. There are some issues I've noticed in your connect/disconnect implementation that I haven't had a chance to comment on, yet. I've tested ocelot-8021q plus the tagging protocol change and these appear fine. I'd like to post the changes I have, to make sure that what works for me works for you, and what works for you works for me. I may also have some patches laying around that track the master up/down state (I needed those for some RFC DSA master change patches). I'll build a mini patch series and post it soon-ish.