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

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Date:	Thu, 27 Dec 2012 22:25:42 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Tony Luck <tony.luck@...el.com>,
	"H. Peter Anvin" <hpa@...or.com>, Jiang Liu <liuj97@...il.com>,
	Myron Stowe <myron.stowe@...hat.com>
Subject: Re: [Alternative][PATCH] ACPI / PCI: Set root bridge ACPI handle in advance

On Thursday, December 27, 2012 02:31:09 PM Rafael J. Wysocki wrote:
> On Thursday, December 27, 2012 01:47:22 PM Rafael J. Wysocki wrote:
> > On Wednesday, December 26, 2012 04:10:32 PM Yinghai Lu wrote:
> > > On Wed, Dec 26, 2012 at 2:36 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> > > > On Wednesday, December 26, 2012 12:41:05 PM Yinghai Lu wrote:
> > > >> On Wed, Dec 26, 2012 at 12:16 PM, Yinghai Lu <yinghai@...nel.org> wrote:
> > > >> > On Wed, Dec 26, 2012 at 12:10 PM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
> > > >> >> Do you have a reference for this?  I think this might have been true
> > > >> >> in the past, but I don't think it's true for any version of gcc we
> > > >> >> support for building Linux.
> > > >> >
> > > >> > http://lkml.indiana.edu/hypermail/linux/kernel/0804.3/3600.html
> > > >>
> > > >> the problem is already addressed by:
> > > >>
> > > >> | commit f9d14250071eda9972e4c9cea745a11185952114
> > > >> | Author: Linus Torvalds <torvalds@...ux-foundation.org>
> > > >> | Date:   Fri Jan 2 09:29:43 2009 -0800
> > > >> |
> > > >> |    Disallow gcc versions 4.1.{0,1}
> > > >> |
> > > >> |    These compiler versions are known to miscompile __weak functions and
> > > >> |    thus generate kernels that don't necessarily work correctly.  If a weak
> > > >> |    function is int he same compilation unit as a caller, gcc may end up
> > > >> |    inlining it, and thus binding the weak function too early.
> > > >> |
> > > >> |    See
> > > >> |
> > > >> |        http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27781
> > > >> |
> > > >> |    for details.
> > > >>
> > > >> so it is ok to put the __weak in the same file now.
> > > >
> > > > Cool, thanks for checking and for the ACK!
> > > 
> > > wait, we have some problem on systems that root bus is not exported via DSDT ...
> > > 
> > > one of my nehalem system that have uncore cpu devices are not exported via ACPI.
> > > 
> > > also there will be problem that system is booting with acpi=off.
> > > 
> > > 
> > > +int pcibios_root_bridge_prepare(struct pci_host_bridge *bridge)
> > > +{
> > > +       struct pci_sysdata *sd = bridge->bus->sysdata;
> > > +       struct pci_root_info *info = container_of(sd, struct pci_root_info, sd);
> > > +
> > > +       ACPI_HANDLE_SET(&bridge->dev, info->bridge->handle);
> > > +       return 0;
> > > +}
> > > 
> > > will get wrong info...via sd... as their sd is standalone
> > 
> > Yes, it will be called in all code paths leading to acpi_create_root_bus(),
> > not only the ones started by pci_acpi_scan_root().  Well, too bad.
> 
> s/acpi_create_root_bus/pci_create_root_bus/
> 
> Sorry.
> 
> > By the way, that illustrates nicely why I generally have concerns about __weak
> > stuff and similar tricks.
> > 
> > Bjorn, I had tried to use the approach you suggested, but it didn't work.
> > I thought about fixing that, but everything I could come up with turned out to
> > be too complicated, so I'm inclined to use the previous version after all:
> > 
> > https://patchwork.kernel.org/patch/1889221/
> > 
> > that has been acked by Yinghai, Greg and Peter already.

I think I know how to avoid the __weak thing without doing what the first
version did.  I'll post a new version of the patch shortly.

Thanks,
Rafael


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