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=-4.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 08785C61DD8 for ; Mon, 16 Nov 2020 19:23:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BF1B82225B for ; Mon, 16 Nov 2020 19:23:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="VIZWt/gj" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729051AbgKPTXY (ORCPT ); Mon, 16 Nov 2020 14:23:24 -0500 Received: from mail.kernel.org ([198.145.29.99]:33724 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725379AbgKPTXX (ORCPT ); Mon, 16 Nov 2020 14:23:23 -0500 Received: from localhost (189.sub-72-105-114.myvzw.com [72.105.114.189]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id EBB302225B; Mon, 16 Nov 2020 19:23:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1605554602; bh=g0rPF891hY5n20OTuoyLNjb51WCLMjcMNMxWkW5x6r4=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=VIZWt/gjTQ1W6GTJzcOu2+w+1Ha5xbdud4IgZiDCWP5doSWm55i2h73+907fxRY16 ibe+ErD/e4baLmQZPeoImfqKuVP/mYVU4OAv/a/9SFT9FhIXpPXvWsQ1jhpbDlsaAD 9lyN61KTZBXdK6L+bzT8WvWOe3BJnFmsF9J6KIkI= Date: Mon, 16 Nov 2020 13:23:20 -0600 From: Bjorn Helgaas To: "Rafael J. Wysocki" Cc: "David E. Box" , Bjorn Helgaas , Len Brown , Linux PCI , Linux PM , Linux Kernel Mailing List Subject: Re: [PATCH] PCI: Disable PTM during suspend on Intel PCI bridges Message-ID: <20201116192320.GA1290192@bjorn-Precision-5520> 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-kernel@vger.kernel.org On Mon, Nov 16, 2020 at 06:53:09PM +0100, Rafael J. Wysocki wrote: > On Wed, Oct 7, 2020 at 7:10 PM Bjorn Helgaas wrote: > > On Wed, Oct 07, 2020 at 06:53:16PM +0200, Rafael J. Wysocki wrote: > > > On Wed, Oct 7, 2020 at 6:49 PM David E. Box wrote: > > > > > > > > On Intel Platform Controller Hubs (PCH) since Cannon Lake, the Precision > > > > Time Measurement (PTM) capability can prevent PCIe root ports from power > > > > gating during suspend-to-idle, causing increased power consumption on > > > > systems that suspend using Low Power S0 Idle [1]. The issue is yet to be > > > > root caused but believed to be coming from a race condition in the suspend > > > > flow as the incidence rate varies for different platforms on Linux but the > > > > issue does not occur at all in other operating systems. For now, disable > > > > the feature on suspend on all Intel root ports and enable again on resume. > > > > > > IMV it should also be noted that there is no particular reason why PTM > > > would need to be enabled while the whole system is suspended. At > > > least it doesn't seem to be particularly useful in that state. > > > > Is this a hardware erratum? If not, and this is working as designed, > > it sounds like we'd need to apply this quirk to every device that > > supports PTM. That's not really practical. > > Why not? My objection was that the original patch is a quirk that applies only to Intel devices. If this is a generic thing that should be done for *all* devices that support PTM, that's fine, but it should not be a quirk, and it should not involve a list of Vendor or Device IDs. > It looks like the capability should be saved by pci_save_state() (it > isn't ATM, which appears to be a mistake) and restored by > pci_restore_state(), so if that is implemented, the saving can be > combined with the disabling in principle. Yup, looks like a mistake. Maybe David can fix that at the same time (probably a separate patch, though). I don't have a way to test it, but he probably does. > > The bugzilla says "there is no erratum as this does not affect > > Windows," but that doesn't answer the question. What I want to know > > is whether this is a *hardware* defect and whether it will be fixed in > > future hardware. > > I cannot answer this question, sorry. > > ATM we only know that certain SoCs may not enter the deepest idle > state if PTM is enabled on some PCIe root ports during suspend. > > Disabling PTM on those ports while suspending helps and hence the patch. > > It doesn't appear to qualify as a "hardware defect". > > > If it's a "wont-fix" hardware issue, we can just disable PTM > > completely on Intel hardware and we won't have to worry about it > > during suspend. > > I'm not following the logic here, sorry again. > > First of all, there are systems that never suspend, so why would they > be affected by the remedy (whatever it is)? > > Second, it is not about the suspend failing entirely. It's about > being able to make the system draw less power while suspended. > > Generally, if someone said "I can make the system draw less power > while suspended if I disable PCIe feature X during suspend", would you > disregard that? My questions were all prompted by the Intel-specific nature of the original patch, which suggests an ongoing maintenance burden. If it can be done generically, I have no problem with it. Bjorn