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@xxxxxxx> wrote: > > From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> > > > > 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@xxxxxxxxx> > > Acked-by: Yinghai Lu <yinghai@xxxxxxxxxx> > > and the ones in your acpi_scan_temp branches. Thanks! -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center. -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
