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

[Nirmal Patel <nirmal.patel@linux.intel.com>]

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?
> 
> I think this warrants some clarification and possibly discussion in
> the PCI firmware SIG.
> 
> At the very least, the commit log should mention _OSC and say
> something about the fact that this is assuming PCIe hotplug ownership
> for devices below VMD, regardless of what the upstream _OSC said.
I will make an adjustment to the commit log once we have some
aggrement.
> 
> > Signed-off-by: Nirmal Patel <nirmal.patel@linux.intel.com>
> > ---
> > ---
> >  drivers/pci/controller/vmd.c | 11 ++++++++++-
> >  1 file changed, 10 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/pci/controller/vmd.c
> > b/drivers/pci/controller/vmd.c
> > index 769eedeb8802..e39eaef5549a 100644
> > --- a/drivers/pci/controller/vmd.c
> > +++ b/drivers/pci/controller/vmd.c
> > @@ -720,6 +720,7 @@ static int vmd_enable_domain(struct vmd_dev
> > *vmd, unsigned long features)
> >  	resource_size_t membar2_offset = 0x2000;
> >  	struct pci_bus *child;
> >  	struct pci_dev *dev;
> > +	struct pci_host_bridge *vmd_bridge;
> >  	int ret;
> >  
> >  	/*
> > @@ -886,8 +887,16 @@ static int vmd_enable_domain(struct vmd_dev
> > *vmd, unsigned long features)
> >  	 * and will fail pcie_bus_configure_settings() early. It can
> > instead be
> >  	 * run on each of the real root ports.
> >  	 */
> > -	list_for_each_entry(child, &vmd->bus->children, node)
> > +	vmd_bridge = to_pci_host_bridge(vmd->bus->bridge);
> > +	list_for_each_entry(child, &vmd->bus->children, node) {
> >  		pcie_bus_configure_settings(child);
> > +		/*
> > +		 * When Hotplug is enabled on vmd root-port, enable it
> > on vmd
> > +		 * bridge.
> > +		 */
> > +		if (child->self->is_hotplug_bridge)
> > +			vmd_bridge->native_pcie_hotplug = 1;
> > +	}
> >  
> >  	pci_bus_add_devices(vmd->bus);
> >  
> > -- 
> > 2.31.1
> >