linux-kernel - Re: [Update][PATCH] ACPI / PCI: Set root bridge ACPI handle in advance

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Date:	Mon, 17 Dec 2012 09:24:14 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	David Miller <davem@...emloft.net>, tony.luck@...el.com,
	"H. Peter Anvin" <hpa@...or.com>, Jiang Liu <liuj97@...il.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Jan Glauber <jang@...ux.vnet.ibm.com>
Subject: Re: [Update][PATCH] ACPI / PCI: Set root bridge ACPI handle in advance

On Mon, Dec 17, 2012 at 4:20 AM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.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@...el.com>

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

and the ones in your acpi_scan_temp branches.

Thanks a lot.

Yinghai
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