Message-ID: <6849411.jDP7VSUtXm@vostro.rjw.lan>
Date:	Mon, 17 Dec 2012 08:51:05 +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>
Subject: Re: [PATCH] ACPI / PCI: Set root bridge ACPI handle in advance

On Sunday, December 16, 2012 09:27:49 PM Yinghai Lu wrote:
> On Sun, Dec 16, 2012 at 2:25 PM, 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_node" 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.
> >
> > Only x86 and ia64 are affected directly, there should be no
> > functional changes resulting from this on other architectures.
> 
> that is good one to avoid that find_root_bridge...
> 
> >
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > ---
> >
> > Should apply to the current Linus' tree, boots correctly on x86(-64).

> >
> > ---
> >  arch/ia64/pci/pci.c              |    5 ++++-
> >  arch/powerpc/kernel/pci-common.c |    3 ++-
> >  arch/sparc/kernel/pci.c          |    3 ++-
> >  arch/x86/pci/acpi.c              |    5 ++++-
> >  drivers/acpi/pci_root.c          |   18 ------------------
> >  drivers/pci/pci-acpi.c           |   19 -------------------
> >  drivers/pci/probe.c              |   16 +++++++++++-----
> >  include/acpi/acpi_bus.h          |    1 -
> >  include/linux/pci.h              |    9 ++++++++-
> >  9 files changed, 31 insertions(+), 48 deletions(-)
> 
> you need to update other arch for pci_create_root_bus
> 
> arch/powerpc/kernel/pci-common.c:       bus =
> pci_create_root_bus(hose->parent, hose->first_busno,

I thought I addressed this one, didn't I?

> arch/s390/pci/pci.c:    zdev->bus = pci_create_root_bus(NULL,
> ZPCI_BUS_NR, &pci_root_ops,

This one appears to have been removed.  There's no pci_create_root_bus()
in all arch/s390, as far as I can say.

> arch/sparc/kernel/pci.c:        bus = pci_create_root_bus(parent,
> pbm->pci_first_busno, pbm->pci_ops,

I modified this one too, is that not sufficient?

> drivers/parisc/dino.c:  dino_dev->hba.hba_bus = bus =
> pci_create_root_bus(&dev->dev,
> drivers/parisc/lba_pci.c:               pci_create_root_bus(&dev->dev,
> lba_dev->hba.bus_num.start,

These two pass NULL as the 4th argument to pci_create_root_bus() and don't
need to be updated, AFAICS.

> >
> > Index: linux/arch/x86/pci/acpi.c
> > ===================================================================
> > --- linux.orig/arch/x86/pci/acpi.c
> > +++ linux/arch/x86/pci/acpi.c
> > @@ -450,6 +450,7 @@ struct pci_bus * __devinit pci_acpi_scan
> >         LIST_HEAD(resources);
> >         struct pci_bus *bus = NULL;
> >         struct pci_sysdata *sd;
> > +       struct pci_root_sys_info si;
> >         int node;
> >  #ifdef CONFIG_ACPI_NUMA
> >         int pxm;
> > @@ -486,6 +487,8 @@ struct pci_bus * __devinit pci_acpi_scan
> >         sd = &info->sd;
> >         sd->domain = domain;
> >         sd->node = node;
> > +       si.acpi_node.handle = device->handle;
> > +       si.sysdata = sd;
> 
> maybe you can try to have si.acpi_handle directly ?

I did it this way for handle to be compiled out when CONFIG_ACPI is not set
(struct acpi_dev_node is an empty structure in that case).

Thanks,
Rafael


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