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 68FA9C433EF for ; Wed, 9 Feb 2022 21:36:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233588AbiBIVgt (ORCPT ); Wed, 9 Feb 2022 16:36:49 -0500 Received: from gmail-smtp-in.l.google.com ([23.128.96.19]:45282 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233507AbiBIVgm (ORCPT ); Wed, 9 Feb 2022 16:36:42 -0500 Received: from sin.source.kernel.org (sin.source.kernel.org [IPv6:2604:1380:40e1:4800::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3DD55C102FD8; Wed, 9 Feb 2022 13:36:44 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by sin.source.kernel.org (Postfix) with ESMTPS id A9CE1CE2299; Wed, 9 Feb 2022 21:36:42 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 21F57C340E7; Wed, 9 Feb 2022 21:36:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1644442600; bh=eNht/WhgzI8HFTOVd2yW6iJsHrqt1HK/5VYfUBwQ1uM=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=JUwNLoEq61UWVbFsZ2V+yv+PvSSsVPz5tNr5QxdlYhj22VaLg9iAVui4YIh8tapzj iLN54K9XL2kynxSnFzf0FOkYC9ggxOw+OeE/RiAn5kXrCmEx1QU5iP8rBtFvhd7YDO i8AGWJv5HGyHDgCLutrG1D9MHBCO+Nbj8iDk6PXaRu5VjiUlD5B6STNGV0mHSL2U23 3m1NvYk567QRt4Blysx3IKfXJlEnX9xMoc9zUNdoBIsIjg8Ahgdd4izuV64XPVXR9x BitoHIZmPT6A+wGbRUhZx4xUGgp7vY5JAJAspX+GK4xBdWRsovJ4sP+JFUahq2gjWt Yz8czzi7mY4tA== Date: Wed, 9 Feb 2022 15:36:38 -0600 From: Bjorn Helgaas To: "Rafael J. Wysocki" Cc: Keith Busch , Kai-Heng Feng , Bjorn Helgaas , Linux PM , Nirmal Patel , Jonathan Derrick , Lorenzo Pieralisi , Rob Herring , Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= , Linux PCI , Linux Kernel Mailing List Subject: Re: [PATCH v3] PCI: vmd: Honor ACPI _OSC on PCIe features Message-ID: <20220209213638.GA587920@bhelgaas> 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 Tue, Dec 07, 2021 at 02:15:04PM +0100, Rafael J. Wysocki wrote: > On Tue, Dec 7, 2021 at 12:12 AM Keith Busch wrote: > > On Fri, Dec 03, 2021 at 11:15:41AM +0800, Kai-Heng Feng wrote: > > > When Samsung PCIe Gen4 NVMe is connected to Intel ADL VMD, the > > > combination causes AER message flood and drags the system performance > > > down. > > > > > > The issue doesn't happen when VMD mode is disabled in BIOS, since AER > > > isn't enabled by acpi_pci_root_create() . When VMD mode is enabled, AER > > > is enabled regardless of _OSC: > > > [ 0.410076] acpi PNP0A08:00: _OSC: platform does not support [AER] > > > ... > > > [ 1.486704] pcieport 10000:e0:06.0: AER: enabled with IRQ 146 > > > > > > Since VMD is an aperture to regular PCIe root ports, honor ACPI _OSC to > > > disable PCIe features accordingly to resolve the issue. > > > > At least for some versions of this hardare, I recall ACPI is unaware of > > any devices in the VMD domain; the platform can not see past the VMD > > endpoint, so I throught the driver was supposed to always let the VMD > > domain use OS native support regardless of the parent's ACPI _OSC. > > This is orthogonal to whether or not ACPI is aware of the VMD domain > or the devices in it. > > If the platform firmware does not allow the OS to control specific > PCIe features at the physical host bridge level, that extends to the > VMD "bus", because it is just a way to expose a hidden part of the > PCIe hierarchy. I don't understand what's going on here. Do we understand the AER message flood? Are we just papering over it by disabling AER? If an error occurs below a VMD, who notices and reports it? If we disable native AER below VMD because of _OSC, as this patch does, I guess we're assuming the platform will handle AER events below VMD. Is that really true? Does the platform know how to find AER log registers of devices below VMD? > The platform firmware does that through ACPI _OSC under the host > bridge device (not under the VMD device) which it is very well aware > of.