Re: [PATCH] PCI: ACPI: Fix up ACPI companion lookup for device 0 on the root bus

From: Bjorn Helgaas
Date: Fri Dec 11 2020 - 18:23:44 EST


On Fri, Dec 11, 2020 at 09:17:35PM +0100, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
>
> In some cases acpi_pci_find_companion() returns an incorrect device
> object as the ACPI companion for device 0 on the root bus (bus 0).
>
> On the affected systems that device is the PCI interface to the
> host bridge and the "ACPI companion" returned for it corresponds
> to a non-PCI device located in the SoC (e.g. a sensor on an I2C
> bus). As a result of this, the ACPI device object "attached"
> to PCI device 00:00.0 cannot be used for enumerating the device
> that is really represented by it which (of course) is problematic.
>
> Address that issue by preventing acpi_pci_find_companion() from
> returning a device object with a valid _HID (which by the spec
> should not be present uder ACPI device objects corresponding to
> PCI devices) for PCI device 00:00.0.
>
> Link: https://lore.kernel.org/linux-acpi/1409ba0c-1580-dc09-e6fe-a0c9bcda6462@xxxxxxxxx/
> Reported-by: Daniel Scally <djrscally@xxxxxxxxx>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

Applied with Daniel's Tested-by and Reviewed-by to pci/enumeration for
v5.11, thanks!

> ---
> drivers/pci/pci-acpi.c | 20 +++++++++++++++++++-
> 1 file changed, 19 insertions(+), 1 deletion(-)
>
> Index: linux-pm/drivers/pci/pci-acpi.c
> ===================================================================
> --- linux-pm.orig/drivers/pci/pci-acpi.c
> +++ linux-pm/drivers/pci/pci-acpi.c
> @@ -1162,14 +1162,32 @@ void acpi_pci_remove_bus(struct pci_bus
> static struct acpi_device *acpi_pci_find_companion(struct device *dev)
> {
> struct pci_dev *pci_dev = to_pci_dev(dev);
> + struct acpi_device *adev;
> bool check_children;
> u64 addr;
>
> check_children = pci_is_bridge(pci_dev);
> /* Please ref to ACPI spec for the syntax of _ADR */
> addr = (PCI_SLOT(pci_dev->devfn) << 16) | PCI_FUNC(pci_dev->devfn);
> - return acpi_find_child_device(ACPI_COMPANION(dev->parent), addr,
> + adev = acpi_find_child_device(ACPI_COMPANION(dev->parent), addr,
> check_children);
> + /*
> + * There may be ACPI device objects in the ACPI namespace that are
> + * children of the device object representing the host bridge, but don't
> + * represent PCI devices. Both _HID and _ADR may be present for them,
> + * even though that is against the specification (for example, see
> + * Section 6.1 of ACPI 6.3), but in many cases the _ADR returns 0 which
> + * appears to indicate that they should not be taken into consideration
> + * as potential companions of PCI devices on the root bus.
> + *
> + * To catch this special case, disregard the returned device object if
> + * it has a valid _HID, addr is 0 and the PCI device at hand is on the
> + * root bus.
> + */
> + if (adev && adev->pnp.type.platform_id && !addr && !pci_dev->bus->parent)
> + return NULL;
> +
> + return adev;
> }
>
> /**
>
>
>