Re: [PATCH v3] PCI: vmd: Honor ACPI _OSC on PCIe features

[Keith Busch <kbusch@kernel.org>]

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.

 
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=215027
> Suggested-by: Rafael J. Wysocki <rafael@kernel.org>
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
> ---
> v3:
>  - Use a new helper function.
> 
> v2:
>  - Use pci_find_host_bridge() instead of open coding.
> 
>  drivers/pci/controller/vmd.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
> index a45e8e59d3d48..691765e6c12aa 100644
> --- a/drivers/pci/controller/vmd.c
> +++ b/drivers/pci/controller/vmd.c
> @@ -661,6 +661,21 @@ static int vmd_alloc_irqs(struct vmd_dev *vmd)
>  	return 0;
>  }
>  
> +/*
> + * Since VMD is an aperture to regular PCIe root ports, only allow it to
> + * control features that the OS is allowed to control on the physical PCI bus.
> + */
> +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;
> +	vmd_bridge->native_dpc = root_bridge->native_dpc;
> +}
> +
>  static int vmd_enable_domain(struct vmd_dev *vmd, unsigned long features)
>  {
>  	struct pci_sysdata *sd = &vmd->sysdata;
> @@ -798,6 +813,9 @@ static int vmd_enable_domain(struct vmd_dev *vmd, unsigned long features)
>  		return -ENODEV;
>  	}
>  
> +	vmd_copy_host_bridge_flags(pci_find_host_bridge(vmd->dev->bus),
> +				   to_pci_host_bridge(vmd->bus->bridge));
> +
>  	vmd_attach_resources(vmd);
>  	if (vmd->irq_domain)
>  		dev_set_msi_domain(&vmd->bus->dev, vmd->irq_domain);
> -- 
> 2.32.0
>