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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8CFBDC4332F for ; Tue, 12 Dec 2023 21:27:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1377374AbjLLV1I (ORCPT ); Tue, 12 Dec 2023 16:27:08 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41622 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235196AbjLLV1E (ORCPT ); Tue, 12 Dec 2023 16:27:04 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 69AEFFD for ; Tue, 12 Dec 2023 13:27:10 -0800 (PST) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 82447C433C7; Tue, 12 Dec 2023 21:27:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1702416430; bh=dswbdDQkq9R1rqLEQPK78MDzN2SBMjw7O1v1jhL3dU4=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=r5Q7DnGGEGhJChFt9UzIVBp28k4PNZQGG3QDcSIoEbRCqDHkk1/x+AZynmP5SKQy1 8sYavtfW2mETOwNUcbgsiTi7SIbNF6x5Ld7NVxdgKyyCmZN+CVgSiaXpuacBLP/D8a YJSgzrt9VlXDXRA4oiQXbfmeM9SgZzYXvffVfDRGO5QsiI7Ix2HPCiCWe7IWC03RJZ uyNrfJoL/abXRAV95IvqkTJHRlHFzsL+c2rKHGYdb+k0G1U8E3w9/zBGSyTRKPVe6y qcqiN7g7G7hry8Y3pkrVhlnRxEp8/DdQop2rAkqd3TuohbEzDwkKzjV4k8Qbk2FYbV nUEXOkCGRFvSg== Date: Tue, 12 Dec 2023 15:27:07 -0600 From: Bjorn Helgaas To: Kai-Heng Feng Cc: Johan Hovold , Lorenzo Pieralisi , Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= , Bjorn Helgaas , Andy Gross , Bjorn Andersson , Konrad Dybcio , Manivannan Sadhasivam , Rob Herring , Nirmal Patel , Jonathan Derrick , linux-arm-msm@vger.kernel.org, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Michael Bottini , "David E . Box" , Manivannan Sadhasivam Subject: Re: [PATCH v2 1/6] PCI/ASPM: Add locked helper for enabling link state Message-ID: <20231212212707.GA1021099@bhelgaas> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 12, 2023 at 11:48:27AM +0800, Kai-Heng Feng wrote: > On Fri, Dec 8, 2023 at 4:47 AM Bjorn Helgaas wrote: > ... > > I hope we can obsolete this whole idea someday. Using pci_walk_bus() > > in qcom and vmd to enable ASPM is an ugly hack to work around this > > weird idea that "the OS isn't allowed to enable more ASPM states than > > the BIOS did because the BIOS might have left ASPM disabled because it > > knows about hardware issues." More history at > > https://lore.kernel.org/linux-pci/20230615070421.1704133-1-kai.heng.feng@canonical.com/T/#u > > > > I think we need to get to a point where Linux enables all supported > > ASPM features by default. If we really think x86 BIOS assumes an > > implicit contract that the OS will never enable ASPM more > > aggressively, we might need some kind of arch quirk for that. > > The reality is that PC ODM toggles ASPM to workaround hardware > defects, assuming that OS will honor what's set by the BIOS. > If ASPM gets enabled for all devices, many devices will break. That's why I mentioned some kind of arch quirk. Maybe we're forced to do that for x86, for instance. But even that is a stop-gap. The idea that the BIOS ASPM config is some kind of handoff protocol is really unsupportable. Do we have concrete examples of where enabling ASPM for a device that advertises ASPM support will break something? Bjorn