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=-2.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 B7FCDC4320A for ; Wed, 1 Sep 2021 01:38:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9ADB46102A for ; Wed, 1 Sep 2021 01:38:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241659AbhIABjc (ORCPT ); Tue, 31 Aug 2021 21:39:32 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49238 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241332AbhIABja (ORCPT ); Tue, 31 Aug 2021 21:39:30 -0400 Received: from mail-wm1-x330.google.com (mail-wm1-x330.google.com [IPv6:2a00:1450:4864:20::330]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 154E8C061575; Tue, 31 Aug 2021 18:38:34 -0700 (PDT) Received: by mail-wm1-x330.google.com with SMTP id u15-20020a05600c19cf00b002f6445b8f55so422187wmq.0; Tue, 31 Aug 2021 18:38:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=c49lwdNA/4qGxRGlAzlwlSfsQDVL/K1bY/Nkb8zzaXg=; b=AbMa/KUyypBDufyOqz4wJPuw2x+lZdQCoFLpvgMy1W6uw5FFb47QtRwmaXdxHZbxFu yTlJNChjDVVFqfqwjQFL5Zfa78dJ1b7lLidnPy7/L9zAOTi6cH+eUquKvfbqACP7b4yR TV9U8Jlx6XXKJaf6IDRSKBa8NDrqn/e0SavG3eDPxb2VyAxOPyW3QI7tMixIB64rzVNh 5yhSLKd5Nou51cWoeSN4tHvbnoDSPg8FTB952BWNazDjQbcCjZkn7m0iMfcCrjs5840V 1o5/ctKk7SdhfXEemg0a03wUd4ldy39qYRiiQ4G6KDGBVhNl5HtpsW26i0nYp13en3tt tOzA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=c49lwdNA/4qGxRGlAzlwlSfsQDVL/K1bY/Nkb8zzaXg=; b=OD96m+yMFoy1CrpSEaKygsLRPu2JrD/bvIkrPFLfxBvenIDyCU+dTHXGgwEUHR6UxD xjZ7IFlF5u1r998C52r0X1GOSqgNYJMuiu4/5+VNxg6IyrVi0qZka7KtfcIuCLoPIm2A WEYh/1N3KCzK1JRNQaV5rzOMCCGM3FpVYNQ42n0xeJ5qJlPl8C/v7nnzw2o5LpQjCdjn o+5JglkYcETwu3y3RUiDQ682aJTdRxhid0tNuH4tHhydlMlq3aY2Bv0Xw0bBVivV/Vu+ qqhl3RPfiO3AiorP2kXqnbNpb450OUXJlGoeStnW71viQSiNGcxn9duZCeUEsc+V/MsK W9sQ== X-Gm-Message-State: AOAM530B1WWvR4CqyUaI/0I8gjekcWSOgIjljt0Vp8qlF/9os5BRn7qW v6JWobzwqMjXzfouzr5wb5o= X-Google-Smtp-Source: ABdhPJzKmvo340pSwM8AWaBWhIsp3haAr5eQW7IdhXgF35mMM0RkJysBNtGnwqClIIBpbb/2TR7A4A== X-Received: by 2002:a05:600c:219:: with SMTP id 25mr6838668wmi.157.1630460312645; Tue, 31 Aug 2021 18:38:32 -0700 (PDT) Received: from skbuf ([82.78.148.104]) by smtp.gmail.com with ESMTPSA id d6sm17752023wra.5.2021.08.31.18.38.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 31 Aug 2021 18:38:32 -0700 (PDT) Date: Wed, 1 Sep 2021 04:38:30 +0300 From: Vladimir Oltean To: Andrew Lunn Cc: Saravana Kannan , Greg Kroah-Hartman , "Rafael J. Wysocki" , Linus Walleij , Vivien Didelot , Florian Fainelli , "David S. Miller" , Jakub Kicinski , Len Brown , Alvin Sipraga , kernel-team@android.com, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, linux-acpi@vger.kernel.org Subject: Re: [PATCH v1 1/2] driver core: fw_devlink: Add support for FWNODE_FLAG_BROKEN_PARENT Message-ID: <20210901013830.yst73ubhsrlml54i@skbuf> References: <20210831231804.zozyenear45ljemd@skbuf> <20210901012826.iuy2bhvkrgahhrl7@skbuf> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210901012826.iuy2bhvkrgahhrl7@skbuf> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 01, 2021 at 04:28:26AM +0300, Vladimir Oltean wrote: > On Wed, Sep 01, 2021 at 02:18:04AM +0300, Vladimir Oltean wrote: > > On Wed, Sep 01, 2021 at 01:02:09AM +0200, Andrew Lunn wrote: > > > Rev B is interesting because switch0 and switch1 got genphy, while > > > switch2 got the correct Marvell PHY driver. switch2 PHYs don't have > > > interrupt properties, so don't loop back to their parent device. > > > > This is interesting and not what I really expected to happen. It goes to > > show that we really need more time to understand all the subtleties of > > device dependencies before jumping on patching stuff. > > There is an even more interesting variation which I would like to point > out. It seems like a very odd loophole in the device links. > > Take the example of the mv88e6xxx DSA driver. On my board > (arch/arm64/boot/dts/marvell/armada-3720-turris-mox.dts), even after I > had to declare the switches as interrupt controller and add interrupts > to their internal PHYs, I still need considerable force to 'break' this > board in the way discussed in this thread. The correct PHY driver insists > to probe, and not genphy. Let me explain. > > The automatic device links between the switch (supplier, as interrupt-controller) > and PHYs (consumers) are added by fwnode_link_add, called from of_link_to_phandle. > > Important note: fwnode_link_add does not link devices, it links OF nodes. > > Even more important node, in the form of a comment: > > * The driver core will use the fwnode link to create a device link between the > * two device objects corresponding to @con and @sup when they are created. The > * driver core will automatically delete the fwnode link between @con and @sup > * after doing that. > > Okay?! > > What seems to be omitted is that the DSA switch driver's probing itself > can be deferred. For example: > > dsa_register_switch > -> dsa_switch_probe > -> dsa_switch_parse_of > -> dsa_switch_parse_ports_of > -> dsa_port_parse_of > -> of_find_net_device_by_node(of_parse_phandle(dn, "ethernet", 0)); > -> not found => return -EPROBE_DEFER > > When dsa_register_switch() returns -EPROBE_DEFER, it is effectively > an error path. So the reverse of initialization is performed. > > The mv88e6xxx driver calls mv88e6xxx_mdios_register() right _before_ > dsa_register_switch. So when dsa_register_switch returns error code, > mv88e6xxx_mdios_unregister() will be called. > > When mv88e6xxx_mdios_unregister() is called, the MDIO buses with > internal PHYs are destroyed. So the PHY devices themselves are destroyed > too. And the device links between the DSA switch and the internal PHYs, > those created based on the firmware node links created by fwnode_link_add, > are dropped too. > > Now remember the comment that the device links created based on > fwnode_link_add are not restored. > > So probing of the DSA switch finally resumes, and this time > device_links_check_suppliers() is effectively bypassed, the PHYs no > longer request probe deferral due to their supplier not being ready, > because the device link no longer exists. > > Isn't this self-sabotaging?! > > Now generally, DSA drivers defer probing because they probe in parallel > with the DSA master. This is typical if the switch is on a SPI bus, or > I2C, or on an MDIO bus provided by a _standalone_ MDIO controller. > > If the MDIO controller is not standalone, but is provided by Ethernet > controller that is the DSA master itself, then things change a lot, > because probing can never be parallel. The DSA master probes, > initializes its MDIO bus, and this triggers the probing of the MDIO > devices on that bus, one of which is the DSA switch. So DSA can no > longer defer the probe due to that reason. > > Secondly, in DSA we even have variation between drivers as to where they > register their internal MDIO buses. The mv88e6xxx driver does this in > mv88e6xxx_probe (the probe function on the MDIO bus). The rtl8366rb > driver calls realtek_smi_setup_mdio() from rtl8366rb_setup(), and this > is important. DSA provides drivers with a .setup() callback, which is > guaranteed to take place after nothing can defer the switch's probe > anymore. > > So putting two and two together, sure enough, if I move mv88e6xxx_mdios_register > from mv88e6xxx_probe to mv88e6xxx_setup, then I can reliably break this > setup, because the device links framework isn't sabotaging itself anymore. > > Conversely, I am pretty sure that if rtl8366rb was to call of_mdiobus_register() > from the probe method and not the setup method, the entire design issue > with interrupts on internal DSA switch ports would have went absolutely > unnoticed for a few more years. > > I have not tested this, but it also seems plausible that DSA can > trivially and reliably bypass any fw_devlink=on restrictions by simply > moving all of_mdiobus_register() driver calls from the .setup() method > to their respective probe methods (prior to calling dsa_register_switch), > then effectively fabricate an -EPROBE_DEFER during the first probe attempt. > I mean, who will know whether that probe deferral request was justified > or not? Pushing the thought even further, it is not even necessary to move the of_mdiobus_register() call to the probe function. Where it is (in .setup) is already good enough. It is sufficient to return -EOPNOTSUPP once (the first time) immediately _after_ the call to of_mdiobus_register (and have a proper error path, i.e. call mdiobus_unregister too). > Anyway, I'm not sure everyone agrees with this type of "solution" (even > though it's worth pointing it out as a fw_devlink limitation). In any > case, we need some sort of lightweight "fix" to the chicken-and-egg > problem, which will give me enough time to think of something better. > I hope it is at least clearer now that there are subtleties and nuances, > and we cannot just assess how many boards are broken by looking at the > device trees. By design, all are, sure, but they might still work, and > that's better than nothing...