Re: [PATCH v2] PCI: vmd: Honor ACPI _OSC on PCIe features

["Rafael J. Wysocki" <rafael@kernel.org>]

On Thu, Dec 2, 2021 at 4:05 AM Kai-Heng Feng
<kai.heng.feng@canonical.com> 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.
>
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=215027
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
> ---
> v2:
>  - Use pci_find_host_bridge() instead of open coding.
>
>  drivers/pci/controller/vmd.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
> index a45e8e59d3d48..acf847cb825c0 100644
> --- a/drivers/pci/controller/vmd.c
> +++ b/drivers/pci/controller/vmd.c
> @@ -671,6 +671,7 @@ static int vmd_enable_domain(struct vmd_dev *vmd, unsigned long features)
>         resource_size_t offset[2] = {0};
>         resource_size_t membar2_offset = 0x2000;
>         struct pci_bus *child;
> +       struct pci_host_bridge *root_bridge, *vmd_bridge;
>         int ret;
>
>         /*
> @@ -798,6 +799,17 @@ static int vmd_enable_domain(struct vmd_dev *vmd, unsigned long features)
>                 return -ENODEV;
>         }
>
> +       vmd_bridge = to_pci_host_bridge(vmd->bus->bridge);
> +
> +       root_bridge = pci_find_host_bridge(vmd->dev->bus);
> +
> +       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;

One more, arguably minor, thing: I would put the above copying into a
separate function and call it here and I would add a comment
explaining why it is done next to it, like

/*
 * 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.
 */
vmd_copy_host_bridge_flags(to_pci_host_bridge(vmd->bus->bridge),
pci_find_host_bridge(vmd->dev->bus));

> +
>         vmd_attach_resources(vmd);
>         if (vmd->irq_domain)
>                 dev_set_msi_domain(&vmd->bus->dev, vmd->irq_domain);
> --
> 2.32.0
>