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 <kbusch@xxxxxxxxxx> 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.
