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 F295BC433DB for ; Thu, 25 Mar 2021 16:28:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C627B61A2C for ; Thu, 25 Mar 2021 16:28:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229508AbhCYQ1t (ORCPT ); Thu, 25 Mar 2021 12:27:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49050 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229448AbhCYQ1f (ORCPT ); Thu, 25 Mar 2021 12:27:35 -0400 Received: from mail-ot1-x330.google.com (mail-ot1-x330.google.com [IPv6:2607:f8b0:4864:20::330]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 557EBC06174A; Thu, 25 Mar 2021 09:27:35 -0700 (PDT) Received: by mail-ot1-x330.google.com with SMTP id t23-20020a0568301e37b02901b65ab30024so2502989otr.4; Thu, 25 Mar 2021 09:27:35 -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=w5Ii9ioTk5DBDRo/eb1vw/NJjq462M7hb+quoEebhFs=; b=SI43kF7g+Di3eYvvOCKPXYO/c3EsrTGm/th0BOeocVpNjJICcBN9UUHDD4o/bnYP4j /+bwOXP0/STQj2eieD/TIfRkLdN5R9xA/lUKm2wrsf6r5YfOrHeVUwnLSk80r/LQHZYo +sQI5Cfahre+9eBCQ7acn1BlWEmuG19HaDVNFmwxjCLRUgue6gV/iq8KYiGcFxxwAG1j 40x8+bzOQe9c5TVcs+vdfFZo1D1iO1WsKpiaiSGgOH7nLW63T76Vddgu857YDBAWvnvh iUBWs8V57Q5ppBKT118ply7Apmrh+A0LtZXJrRhLYnDDerWMMuTKTDrocgxL8zXtbrnj 7rkw== 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=w5Ii9ioTk5DBDRo/eb1vw/NJjq462M7hb+quoEebhFs=; b=jGwKSMFBSV193p3hX2SQ6jG4tp1VC9UbCtvCwFT8cMnJ3C5V7DM+suzax0DNRFeWpH vgJwoLUergAK8jUm3OZwqOgD7HWiEOzdniaW+VSrS11gf4Gk1eOD9055nPD0hk7r60ZM MKBowZdD6OqXwjn2O+Sf64Wc/46GiqxMKCkJnNP/ZgPBiK8DMJkPon1eeXVfeNRfy4Po QlNaMdLtAZ4B3gUAueFvZKE071xCSouoiOm99BbPSWVl7m5bqx+YNuDZXevAQMD9yoAY /Ydu9kvk6R0FCJ+fYxqkYrE+X05r8I56rCJhjz+f2GgHCYpo6TwzZ/kgJ+zqjQtTX6eU 37nQ== X-Gm-Message-State: AOAM5311TxfopUF4kffboyA1QaDmRVi6H3gTYpd8/j1mMcuYQmM2M1ul xnfuQijHIEVVo7AyTmEuJOM= X-Google-Smtp-Source: ABdhPJys8cK7TtoIBv7+WCzlBYVwiw8Ojq/Eh27ptGjRuCb9Dus+boDLq+IejwdFHbcVjdS8M153PQ== X-Received: by 2002:a9d:6951:: with SMTP id p17mr7966095oto.158.1616689654572; Thu, 25 Mar 2021 09:27:34 -0700 (PDT) Received: from localhost ([107.181.165.199]) by smtp.gmail.com with ESMTPSA id z25sm1504626otj.68.2021.03.25.09.27.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 25 Mar 2021 09:27:33 -0700 (PDT) Date: Thu, 25 Mar 2021 21:56:37 +0530 From: Amey Narkhede To: Leon Romanovsky Cc: info@metux.net, raphael.norwitz@nutanix.com, alex.williamson@redhat.com, linux-pci@vger.kernel.org, bhelgaas@google.com, linux-kernel@vger.kernel.org, alay.shah@nutanix.com, suresh.gumpula@nutanix.com, shyam.rajendran@nutanix.com, felipe@nutanix.com Subject: Re: [PATCH 4/4] PCI/sysfs: Allow userspace to query and set device reset mechanism Message-ID: <20210325162637.6ewxkxhvogdsgdxv@archlinux> References: <20210319102313.179e9969@omen.home.shazbot.org> <20210320085942.3cefcc48@x1.home.shazbot.org> <20210322111003.50d64f2c@omen.home.shazbot.org> <20210324083743.791d6191@omen.home.shazbot.org> <20210324111729.702b3942@omen.home.shazbot.org> 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-pci@vger.kernel.org On 21/03/25 10:37AM, Leon Romanovsky wrote: > On Wed, Mar 24, 2021 at 11:17:29AM -0600, Alex Williamson wrote: > > On Wed, 24 Mar 2021 17:13:56 +0200 > > Leon Romanovsky wrote: > > <...> > > > > Yes, and real testing/debugging almost always requires kernel rebuild. > > > Everything else is waste of time. > > > > Sorry, this is nonsense. Allowing users to debug issues without a full > > kernel rebuild is a good thing. > > It is far from debug, this interface doesn't give you any answers why > the reset didn't work, it just helps you to find the one that works. > > Unless you believe that this information will be enough to understand > the root cause, you will need to ask from the user to perform extra > tests, maybe try some quirk. All of that requires from the users to > rebuild their kernel. > > So no, it is not debug. > > > > > > > > > For policy preference, I already described how I've configured QEMU to > > > > > > prefer a bus reset rather than a PM reset due to lack of specification > > > > > > regarding the scope of a PM "soft reset". This interface would allow a > > > > > > system policy to do that same thing. > > > > > > > > > > > > I don't think anyone is suggesting this as a means to avoid quirks that > > > > > > would resolve reset issues and create the best default general behavior. > > > > > > This provides a mechanism to test various reset methods, and thereby > > > > > > identify broken methods, and set a policy. Sure, that policy might be > > > > > > to avoid a broken reset in the interim before it gets quirked and > > > > > > there's potential for abuse there, but I think the benefits outweigh > > > > > > the risks. > > > > > > > > > > This interface is proposed as first class citizen in the general sysfs > > > > > layout. Of course, it will be seen as a way to bypass the kernel. > > > > > > > > > > At least, put it under CONFIG_EXPERT option, so no distro will enable it > > > > > by default. > > > > > > > > Of course we're proposing it to be accessible, it should also require > > > > admin privileges to modify, sysfs has lots of such things. If it's > > > > relegated to non-default accessibility, it won't be used for testing > > > > and it won't be available for system policy and it's pointless. > > > > > > We probably have difference in view of what testing is. I expect from > > > the users who experience issues with reset to do extra steps and one of > > > them is to require from them to compile their kernel. > > > > I would define the ability to generate a CI test that can pick a > > device, unbind it from its driver, and iterate reset methods as a > > worthwhile improvement in testing. > > Who is going to run this CI? At least all kernel CIs (external and > internal to HW vendors) that I'm familiar are building kernel themselves. > > Distro kernel is too bloat to be really usable for CI. > > > > > > The root permissions doesn't protect from anything, SO lovers will use > > > root without even thinking twice. > > > > Yes, with great power comes great responsibility. Many admins ignore > > this. That's far beyond the scope of this series. > > <...> > > > > I'm trying to help you with your use case of providing reset policy > > > mechanism, which can be without CONFIG_EXPERT. However if you want > > > to continue path of having specific reset type only, please ensure > > > that this is not taken to the "bypass kernel" direction. > > > > You've lost me, are you saying you'd be in favor of an interface that > > allows an admin to specify an arbitrary list of reset methods because > > that's somehow more in line with a policy choice than a userspace > > workaround? This seems like unnecessary bloat because (a) it allows > > the same bypass mechanism, and (b) a given device is only going to use > > a single method anyway, so the functionality is unnecessary. Please > > help me understand how this favors the policy use case. Thanks, > > The policy decision is global logic that is easier to grasp. At some > point of our discussion, you presented the case where PM reset is not > defined well and you prefer to do bus reset (something like that). > > I expect that QEMU sets same reset policy for all devices at the same > time instead of trying per-device to guess which one works. > The current reset attribute does the same thing internally you described at the end. > And yes, you will be able to bypass kernel, but at least this interface > will be broader than initial one that serves only SO and workarounds. > What does it mean by "bypassing" kernel? I don't see any problem with SO and workaround if that is the only way an user can use their device. Why are you expecting every vendor to develop quirk? Also I don't see any point of using linked list to unnecessarily complicate a simple thing. Thanks, Amey