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SubjectRe: [Alternative][PATCH] ACPI / PCI: Set root bridge ACPI handle in advance
Date
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@sisk.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@kernel.org> wrote:
> >> > On Wed, Dec 26, 2012 at 12:10 PM, Bjorn Helgaas <bhelgaas@google.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@linux-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.

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.

Thanks,
Rafael


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


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