Re: [PATCH v3] PCI: vmd: Do not change the BIOS Hotplug setting on VMD rootports

[Lorenzo Pieralisi <lpieralisi@kernel.org>]

On Tue, Aug 22, 2023 at 10:45:22AM -0400, Nirmal Patel wrote:
> The hotplug functionality is broken in various combinations of guest
> OSes i.e. RHEL, SLES and hypervisors i.e. KVM and ESXI.
> 
> During the VMD rootport creation, VMD honors ACPI settings and assigns
> respective values to Hotplug, AER, DPC, PM etc which works in case of
> Host OS. But these have been restored back to the power on default
> state in Guest OSes, which puts the root port hot plug enable to
> default OFF.
> 
> The VMD UEFI driver loads and configure all devices under VMD in Host.
> This is how AER, power management, DPC and Hotplug gets enabled.
> Since the Guest BIOS doesn't have VMD UEFI driver, Hotplug  along with
> DPC, AER, PM are Disabled.
> 
> This change will make the VMD Host and Guest Driver to keep the settings
> implemented by the UEFI VMD DXE driver and thus honoring the user
> selections for Hotplug in the BIOS.

It is still unclear, sorry. AFAICS this patch disables native PCI
hotplug and by doing that it allows the guest kernel to keep the
hotplug functionality as programmed by the UEFI driver (in the BIOS).

Is that what it does ? If so write it in the commit log please.

Describe:

(1) Current Host boot
	(1.1) what UEFI/BIOS does
	(1.2) Resulting VMD PCI hotplug configuration
(2) Current Guest boot
	(2.1) Resulting VMD PCI hotplug configuration
(3) Problem to solve
(4) How you are solving it

Please write it to the commit log and then I will merge it.

Thanks,
Lorenzo

> Signed-off-by: Nirmal Patel <nirmal.patel@linux.intel.com>
> ---
> v2->v3: Update commit log.
> v1->v2: Update commit log.
> ---
>  drivers/pci/controller/vmd.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
> index 769eedeb8802..52c2461b4761 100644
> --- a/drivers/pci/controller/vmd.c
> +++ b/drivers/pci/controller/vmd.c
> @@ -701,8 +701,6 @@ static int vmd_alloc_irqs(struct vmd_dev *vmd)
>  static void vmd_copy_host_bridge_flags(struct pci_host_bridge *root_bridge,
>  				       struct pci_host_bridge *vmd_bridge)
>  {
> -	vmd_bridge->native_pcie_hotplug = root_bridge->native_pcie_hotplug;
> -	vmd_bridge->native_shpc_hotplug = root_bridge->native_shpc_hotplug;
>  	vmd_bridge->native_aer = root_bridge->native_aer;
>  	vmd_bridge->native_pme = root_bridge->native_pme;
>  	vmd_bridge->native_ltr = root_bridge->native_ltr;
> -- 
> 2.31.1
>