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SubjectRe: [Update][PATCH] ACPI / PCI: Set root bridge ACPI handle in advance
On Mon, Dec 17, 2012 at 4:20 AM, Rafael J. Wysocki <> wrote:
> From: Rafael J. Wysocki <>
> 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 <>

Acked-by: Yinghai Lu <>

and the ones in your acpi_scan_temp branches.

Thanks a lot.


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