Re: [PATCH] PCI: vmd: Enable Hotplug based on BIOS setting on VMD rootports

[Bjorn Helgaas <helgaas@kernel.org>]

On Tue, Oct 31, 2023 at 12:59:34PM -0700, Nirmal Patel wrote:
> On Tue, 2023-10-31 at 10:31 -0500, Bjorn Helgaas wrote:
> > On Mon, Oct 30, 2023 at 04:16:54PM -0400, Nirmal Patel wrote:
> > > VMD Hotplug should be enabled or disabled based on VMD rootports'
> > > Hotplug configuration in BIOS. is_hotplug_bridge is set on each
> > > VMD rootport based on Hotplug capable bit in SltCap in probe.c.
> > > Check is_hotplug_bridge and enable or disable native_pcie_hotplug
> > > based on that value.
> > > 
> > > Currently VMD driver copies ACPI settings or platform
> > > configurations
> > > for Hotplug, AER, DPC, PM, etc and enables or disables these
> > > features
> > > on VMD bridge which is not correct in case of Hotplug.
> > 
> > This needs some background about why it's correct to copy the ACPI
> > settings in the case of AER, DPC, PM, etc, but incorrect for hotplug.
> > 
> > > Also during the Guest boot up, ACPI settings along with VMD UEFI
> > > driver are not present in Guest BIOS which results in assigning
> > > default values to Hotplug, AER, DPC, etc. As a result Hotplug is
> > > disabled on VMD in the Guest OS.
> > > 
> > > This patch will make sure that Hotplug is enabled properly in Host
> > > as well as in VM.
> > 
> > Did we come to some consensus about how or whether _OSC for the host
> > bridge above the VMD device should apply to devices in the separate
> > domain below the VMD?
>
> We are not able to come to any consensus. Someone suggested to copy
> either all _OSC flags or none. But logic behind that assumption is
> that the VMD is a bridge device which is not completely true. VMD is an
> endpoint device and it owns its domain.

Do you want to facilitate a discussion in the PCI firmware SIG about
this?  It seems like we may want a little text in the spec about how
to handle this situation so platforms and OSes have the same
expectations.

Bjorn