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

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Date:	Tue, 18 Dec 2012 00:13:37 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Yinghai Lu <yinghai@...nel.org>
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 Monday, December 17, 2012 09:24:14 AM Yinghai Lu wrote:
> 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!


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