From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bjorn Helgaas Subject: Re: [PATCH 0/2] PCI/AER: Consistently use _OSC to determine who owns AER Date: Tue, 5 Mar 2019 17:16:51 -0600 Message-ID: <20190305231650.GC215617@google.com> References: <20181115231605.24352-1-mr.nuke.me@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20181115231605.24352-1-mr.nuke.me@gmail.com> Sender: linux-kernel-owner@vger.kernel.org To: Alexandru Gagniuc Cc: helgaas@google.com, austin_bolen@dell.com, alex_gagniuc@dellteam.com, keith.busch@intel.com, Shyam_Iyer@Dell.com, lukas@wunner.de, "Rafael J. Wysocki" , Len Brown , Russell Currey , Sam Bobroff , Oliver O'Halloran , linux-pci@vger.kernel.org, linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org List-Id: linux-acpi@vger.kernel.org On Thu, Nov 15, 2018 at 05:16:01PM -0600, Alexandru Gagniuc wrote: > Thanks to Keith for pointing out that it doesn't make sense to disable > AER services when only one device has a FIRMWARE_FIRST HEST. > > AER ownership is an interesting issue brought in by FFS (firmware-first) > model. In a nutshell if FFS handles AER, then OS should not touch any > of the AER bits. FW might set things up so that it receives AER > notifications via SMI. It's theoretically possible to receive SCIs, > but the exact mechanism is platform-dependent. OS touching AER bits > when firmware owns them may interfere with these notifications. > > The ACPI mechanism for negotiating control of AER is _OSC, and is > described in detail in ACPI 6.2 Ch. 6.2.11.3. _OSC is negotiated at > the root bus level. Any root port, switch, or endpoint under the bus > would have its AER ownership negotiated in one _OSC call. > > Then there is HEST, which is part of ACPI Platform Error Interfaces > (APEI). HEST tables describe the errors that FW may report to the OS. > A types 6,7 and 7 HEST tables describe AER errors from PCIe devices. > As part of this description, we're told if the error source is FFS. > > Information in HEST seems to be redundant, as each error reported by > FW will have a CPER table that describes it in detail. > > Because HEST describes an error source as firmware-first or not, we've > taken this to mean ownership of AER. Because AER ownership and error > reporting are coupled, _OSC and HEST usually agree on the matter of > ownership. However, that doesn't seem to be required by ACPI. > > I've asked around a few people at Dell and they unanimously agree that > _OSC is the correct way to determine ownership of AER. In linux, we > use the result of _OSC to enable AER services, but we use HEST to > determine AER ownership. That's inconsistent. This series drops the > use of HEST in favor of _OSC. > > [1] https://lkml.org/lkml/2018/11/15/62 > > Alexandru Gagniuc (2): > PCI/AER: Do not use APEI/HEST to disable AER services globally > PCI/AER: Determine AER ownership based on _OSC instead of HEST > > drivers/acpi/pci_root.c | 9 +---- > drivers/pci/pcie/aer.c | 82 ++-------------------------------------- > include/linux/pci-acpi.h | 6 --- > 3 files changed, 5 insertions(+), 92 deletions(-) I'm pretty sure we do need to do something here, but there was quite a lot of discussion that didn't seem to really get resolved, so I'm dropping these for now. Please repost them with any relevant updates and we'll see if we can get a consensus that we're going the right direction. Bjorn