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SubjectRe: [Update][PATCH] ACPI / PCI: Set root bridge ACPI handle in advance
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On Monday, December 17, 2012 09:24:14 AM Yinghai Lu wrote:
> On Mon, Dec 17, 2012 at 4:20 AM, Rafael J. Wysocki <rjw@sisk.pl> wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> >
> > 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 <rafael.j.wysocki@intel.com>
>
> Acked-by: Yinghai Lu <yinghai@kernel.org>
>
> and the ones in your acpi_scan_temp branches.

Thanks!


--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.


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