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 31665C432BE for ; Wed, 1 Sep 2021 09:02:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0959D6103D for ; Wed, 1 Sep 2021 09:02:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243365AbhIAJDL (ORCPT ); Wed, 1 Sep 2021 05:03:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37620 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243336AbhIAJDK (ORCPT ); Wed, 1 Sep 2021 05:03:10 -0400 Received: from mail-wm1-x32f.google.com (mail-wm1-x32f.google.com [IPv6:2a00:1450:4864:20::32f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 25DCAC061575; Wed, 1 Sep 2021 02:02:13 -0700 (PDT) Received: by mail-wm1-x32f.google.com with SMTP id u15-20020a05600c19cf00b002f6445b8f55so1018181wmq.0; Wed, 01 Sep 2021 02:02:13 -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=PD5wfgfnh77RuRP2uKllqFvkE7i4Iu1qornbBmeqn3I=; b=M2t8dZQyO7K+Y2KlQQOyoZSztsorIhedH5Z+ynVfPL84/9ZleT/3AvceUhTTovZ7Mp Q7+d/HTQdELYQCUlQ8B+FuhDag4sWpbH050h1pOsIhjfOqxCE9IlGu3d+5/vNZbBLCh+ nP6w5y4Phvz/jO22O7N2o9SeUgqDr2XNpUMP5Eg/lz9EAv8KJskJA08eo6VALn0jWLvv vZ0KvWH97VagDoY3l0dr7fmHvnRYy/+OJI2DnSW5Kb59q1MhQ48asq9DK3a3v6ySmd6h gyVEaMkQZOhME9pEebPtT/HRRzhR1Iym7O4i1l8n9GIHBjbT5qFMfvQnxdXcGnnnA5y8 TFXA== 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=PD5wfgfnh77RuRP2uKllqFvkE7i4Iu1qornbBmeqn3I=; b=R9cVMXfqOXJeIxswAZCPbCqTcQKCEmv+pZJUGx+aBol2j08f2WOOZfx6s1lVHyA5bT O42zWfUPnMHUlBtyHwzjUZ9Jua4rFQ7Wsvuh/Me/UtOO9k1PW+8QttW0JDr+JwnLQUxB CkJnkSOQOeBRjIXNvdBfobE0uaxFDEXxHzhOFW1xzSHxqGk3mumf9gdY+xilaT1MRz0V Fwt1gXJ/Ii8KArWBZ7rea/A7ReElzPJaAaebvn+X3S8dIi70QyteiN4AOuF4JmwyRMau MJ0L7rDz9Ie7QjvIuRmN7nbpLmFCyVlZglQi+juyfWs/apHjVL/ztKRxA8rY9LTJUdaw +hAw== X-Gm-Message-State: AOAM530hhRVCzbPawlZk+GUS+ItPpx9QH3ueIovRuW1KQZNyuJKkjrf4 v8Y7gs13XGgksswpTfTq1v8= X-Google-Smtp-Source: ABdhPJxtT//6ZtQ2O7IF7mVRyWnkykls5bXT0fm0DhUns5lzocjHsmT8hFLdj5HESvKGEnQZPz/8uw== X-Received: by 2002:a7b:c014:: with SMTP id c20mr8503914wmb.81.1630486931446; Wed, 01 Sep 2021 02:02:11 -0700 (PDT) Received: from skbuf ([82.78.148.104]) by smtp.gmail.com with ESMTPSA id n15sm20903742wrv.48.2021.09.01.02.02.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 01 Sep 2021 02:02:10 -0700 (PDT) Date: Wed, 1 Sep 2021 12:02:09 +0300 From: Vladimir Oltean To: Saravana Kannan Cc: Andrew Lunn , 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: <20210901090209.f4na6cwu7lsa57pv@skbuf> References: <20210831231804.zozyenear45ljemd@skbuf> <20210901012826.iuy2bhvkrgahhrl7@skbuf> <20210901013830.yst73ubhsrlml54i@skbuf> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-acpi@vger.kernel.org On Tue, Aug 31, 2021 at 07:19:40PM -0700, Saravana Kannan wrote: > On Tue, Aug 31, 2021 at 6:38 PM Vladimir Oltean wrote: > > > > 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?! > > Yeah, this is a known "issue". I'm saying "issue" because at worst > it'd allow a few unnecessary deferred probes. And if you want to break > or get fw_devlink to ignore your child devices or your consumers, > there are simpler APIs to do it without having to intentionally defer > a probe. Fixing this "issue" would just use up more memory and > increase boot time for no meaningful benefit. But I mean, if the goal of fw_devlink is to infer a probing order based on phandles, and it is faced with a long chain of devices, then any -EPROBE_DEFER of a device on top of the chain will break the probing order for all devices beneath it. It is self-defeating, it is already memory used for nothing. > > > > > > 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). > > Right, there are plenty of ways to intentionally break fw_devlink. I > hope that's not the point :) And I don't think -EOPNOTSUPP would work > because your device wouldn't be probed again. Yes, -EPROBE_DEFER is what I meant. > > > > > 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 think the generic DSA patch I gave would be the lightweight fix to > address this chicken-and-egg issue. > > As for the long term fix, I'd really suggest looking into using the > component device model. I'd even be happy to help make any driver > core/component device improvements you might need. > > I'm also interested in looking into improving the PHY probing so that > the genphy never probes a device that has a driver that could probe > it. Even outside of all this fw_devlink thing, they way PHY is handled > now, if any of the supplier really isn't ready yet (say a clock), then > the genphy gets used -- which isn't good. I think this is the real problem which needs to be addressed. The trouble is, I don't know if phy_attach_direct can find out the reason for which d->driver is NULL, i.e. that there was a driver which matched and attempted the probe, but returned -EPROBE_DEFER. > -Saravana > > > > 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...