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 74122C433B4 for ; Thu, 20 May 2021 23:28:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4CEEE613CE for ; Thu, 20 May 2021 23:28:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234019AbhETX35 (ORCPT ); Thu, 20 May 2021 19:29:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36920 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232547AbhETX34 (ORCPT ); Thu, 20 May 2021 19:29:56 -0400 Received: from forward100j.mail.yandex.net (forward100j.mail.yandex.net [IPv6:2a02:6b8:0:801:2::100]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 625DFC061574; Thu, 20 May 2021 16:28:33 -0700 (PDT) Received: from iva6-26d3dbc69e48.qloud-c.yandex.net (iva6-26d3dbc69e48.qloud-c.yandex.net [IPv6:2a02:6b8:c0c:912f:0:640:26d3:dbc6]) by forward100j.mail.yandex.net (Yandex) with ESMTP id D621F50E1B88; Fri, 21 May 2021 02:28:29 +0300 (MSK) Received: from iva8-174eb672ffa9.qloud-c.yandex.net (iva8-174eb672ffa9.qloud-c.yandex.net [2a02:6b8:c0c:b995:0:640:174e:b672]) by iva6-26d3dbc69e48.qloud-c.yandex.net (mxback/Yandex) with ESMTP id ImeQqByjNU-STJ4wFYl; Fri, 21 May 2021 02:28:29 +0300 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yandex.ru; s=mail; t=1621553309; bh=WrHAGz3ro9Ohp4J6cItIIGrnoXuDOvp2fj40gFEhLsA=; h=In-Reply-To:Cc:To:From:Subject:Message-ID:References:Date; b=jtqJbmT+XyAz1z8YIkYUeJy5exYZjF35as1lVHGKAkfSNGLEXZyD9LBe8A3CI/W6E iPVzVYFtsZN8SHm+lkWMiwUqPatPp2K+wVcrgNvEZ5tDfBSxRdJTOQIw91EuyhDdQy G4cMk0bUkK7lM7/seaCc+bN7wxDcz6e3oWKufUFA= Authentication-Results: iva6-26d3dbc69e48.qloud-c.yandex.net; dkim=pass header.i=@yandex.ru Received: by iva8-174eb672ffa9.qloud-c.yandex.net (smtp/Yandex) with ESMTPSA id TlB44JqxL1-SSLefwCw; Fri, 21 May 2021 02:28:29 +0300 (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)) (Client certificate not present) Message-ID: <15121b9c3ad1683f0d81ebd44ace60509a9a9e82.camel@yandex.ru> Subject: Re: [PATCH] PCI: don't power-off apple thunderbolt controller on s2idle From: Konstantin Kharlamov To: Bjorn Helgaas , "Rafael J. Wysocki" Cc: Lukas Wunner , Linux PCI , "Rafael J. Wysocki" , Andreas Noever , Linux PM Date: Fri, 21 May 2021 02:28:28 +0300 In-Reply-To: <20210520194935.GA348608@bjorn-Precision-5520> References: <20210520194935.GA348608@bjorn-Precision-5520> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.40.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org Thank you very much. Well send then a v2 with the comment in a minute. On Thu, 2021-05-20 at 14:49 -0500, Bjorn Helgaas wrote: > On Thu, May 20, 2021 at 01:54:05PM +0200, Rafael J. Wysocki wrote: > > On Thu, May 20, 2021 at 1:27 PM Rafael J. Wysocki wrote: > > > On Wed, May 19, 2021 at 9:48 PM Bjorn Helgaas wrote: > > > > On Wed, May 19, 2021 at 09:12:26PM +0200, Rafael J. Wysocki wrote: > > > > > > The problem is related to the fact that in s2idle the platform > > > > > firmware does not finalize the suspend transition and, consequently, > > > > > it doesn't initiate the resume transition.  Therefore whatever power > > > > > state the device was left in during suspend must be dealt with during > > > > > the subsequent resume.  Hence, if whatever is done by SXIO/SXFP/SXLF > > > > > in the suspend path cannot be reversed in the resume path by the > > > > > kernel (because there is no known method to do that), they should not > > > > > be invoked.  And that's exactly because the platform firmware will not > > > > > finalize the suspend transition which is indicated by > > > > > PM_SUSPEND_FLAG_FW_SUSPEND being unset. > > > > > > > > How can we connect "if (!pm_suspend_via_firmware())" in this patch > > > > with the fact that firmware doesn't finalize suspend (and consequently > > > > does not reverse things in resume)? > > > > > > > > I don't see any use of pm_suspend_via_firmware() or > > > > PM_SUSPEND_FLAG_FW_SUSPEND that looks relevant. > > > > > > First of all, there is a kerneldoc comment next to > > > pm_suspend_via_firmware() which is relevant.  Especially the last > > > paragraph of that comment applies directly to the case at hand IMV. > > I do read kerneldoc, but I *rely* on the code, and it's nice when I > can match up the kerneldoc with what the code is doing :) > > Part of my confusion is that "passing control to platform firmware" > isn't particularly useful in itself because it doesn't give a clue > about what firmware is *doing*.  Without knowing what it does, we > can't reason about how kernel's actions interact with firmware's > actions. > > > BTW, the problem at hand is not that s2idle in particular needs to be > > treated in a special way (this appears to be the source of all > > confusion here).  The problem is that the kernel cannot undo the > > SXIO/SXFP/SXLF magic without passing control to the platform firmware. > > I assume this is really a case of "the kernel doesn't know *what* to > do, but platform firmware does," so in principle the kernel *could* > undo the SXIO/SXFP/SXLF magic if it knew what to do.  > > > And "passing control to the platform firmware" doesn't mean "executing > > some AML" here, because control remains in the kernel when AML is > > executed.  "Passing control to the platform firmware" means letting > > some native firmware code (like SMM code) run which happens at the end > > of S2/S3/S4 suspend transitions and it does not happen during S1 > > (standby) and s2idle suspend transitions. > > > > That's why using SXIO/SXFP/SXLF is only valid during S2/S3/S4 suspend > > transitions and it is not valid during s2idle and S1 suspend > > transitions (and yes, S1 is also affected, so s2idle is not special in > > that respect at all). > > > > IMO the changelog of the patch needs to be rewritten, but the code > > change made by it is reasonable. > > So IIUC the comment should say something like: > >   SXIO/SXFP/SXLF turns off power to the Thunderbolt controller.  We >   don't know how to turn it back on again, but firmware does, so we >   can only use SXIO/SXFP/SXLF if we're suspending via firmware. > > Actually, it sounds like the important thing is that we rely on the > firmware *resume* path to turn on the power again. > > pm_resume_via_firmware() *sounds* like it would be appropriate, but > the kerneldoc says that's for use after resume, and it tells us > whether firmware has *already* handled the wakeup event.  And > PM_SUSPEND_FLAG_FW_RESUME isn't set until after we've run these > suspend_late fixups, so it wouldn't work here. > > Bjorn