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
