On Mon, Dec 17, 2012 at 4:20 AM, Rafael J. Wysocki [off-list ref] wrote:

From: Rafael J. Wysocki <redacted>

The ACPI handles of PCI root bridges need to be known to
acpi_bind_one(), so that it can create the appropriate
"firmware_node" and "physical_node0" files for them, but currently
the way it gets to know those handles is not exactly straightforward
(to put it lightly).

This is how it works, roughly:

  1. acpi_bus_scan() finds the handle of a PCI root bridge,
     creates a struct acpi_device object for it and passes that
     object to acpi_pci_root_add().

  2. acpi_pci_root_add() creates a struct acpi_pci_root object,
     populates its "device" field with its argument's address
     (device->handle is the ACPI handle found in step 1).

  3. The struct acpi_pci_root object created in step 2 is passed
     to pci_acpi_scan_root() and used to get resources that are
     passed to pci_create_root_bus().

  4. pci_create_root_bus() creates a struct pci_host_bridge object
     and passes its "dev" member to device_register().

  5. platform_notify(), which for systems with ACPI is set to
     acpi_platform_notify(), is called.

So far, so good.  Now it starts to be "interesting".

  6. acpi_find_bridge_device() is used to find the ACPI handle of
     the given device (which is the PCI root bridge) and executes
     acpi_pci_find_root_bridge(), among other things, for the
     given device object.

  7. acpi_pci_find_root_bridge() uses the name (sic!) of the given
     device object to extract the segment and bus numbers of the PCI
     root bridge and passes them to acpi_get_pci_rootbridge_handle().

  8. acpi_get_pci_rootbridge_handle() browses the list of ACPI PCI
     root bridges and finds the one that matches the given segment
     and bus numbers.  Its handle is then used to initialize the
     ACPI handle of the PCI root bridge's device object by
     acpi_bind_one().  However, this is *exactly* the ACPI handle we
     started with in step 1.

Needless to say, this is quite embarassing, but it may be avoided
thanks to commit f3fd0c8 (ACPI: Allow ACPI handles of devices to be
initialized in advance), which makes it possible to initialize the
ACPI handle of a device before passing it to device_register().
Namely, if pci_acpi_scan_root() could easily pass the root bridge's
ACPI handle to pci_create_root_bus(), the latter could set the ACPI
handle in its struct pci_host_bridge object's "dev" member before
passing it to device_register() and steps 6-8 above wouldn't be
necessary any more.

To make that happen I decided to repurpose the 4th argument of
pci_create_root_bus(), because that allowed me to avoid defining
additional callbacks or similar things and didn't seem to impact
architectures without ACPI substantially.

All architectures using pci_create_root_bus() directly are updated
as needed, but only x86 and ia64 are affected as far as the behavior
is concerned (no one else uses ACPI).  There should be no changes in
behavior resulting from this on the other architectures.

Signed-off-by: Rafael J. Wysocki <redacted>

Acked-by: Yinghai Lu <yinghai@kernel.org>

and the ones in your acpi_scan_temp branches.

Thanks a lot.

Yinghai