Re: [PATCH] x86/pci: do assign root bus res if _CRS is used

Gary Hade
2009-04-30T00:06:14Z

On Mon, Apr 27, 2009 at 01:44:01PM -0600, Bjorn Helgaas wrote:
> On Monday 20 April 2009 07:35:40 pm Yinghai Lu wrote:
> > it wil be overwriten later if _CRS is used, so don't bother to set it.
> >
> > [ Impact: cleanup ]
> >
> > Signed-off-by: Yinghai Lu <yinghai@kernel.org>
> >
> > ---
> > arch/x86/pci/amd_bus.c | 4 ++++
> > 1 file changed, 4 insertions(+)
> >
> > Index: linux-2.6/arch/x86/pci/amd_bus.c
> > ===================================================================
> > --- linux-2.6.orig/arch/x86/pci/amd_bus.c
> > +++ linux-2.6/arch/x86/pci/amd_bus.c
> > @@ -100,6 +100,10 @@ void x86_pci_root_bus_res_quirks(struct
> > int j;
> > struct pci_root_info *info;
> >
> > + /* don't go for it if _CRS is used */
> > + if (pci_probe & PCI_USE__CRS)
> > + return;
> > +
> > /* if only one root bus, don't need to anything */
> > if (pci_root_num < 2)
> > return;
>
> This isn't a comment on this patch per se.
>
> I am concerned about the fact that "pci=use_crs" is not the default.
> >From the changelog of 62f420f8282, it sounds like you have to boot an
> IBM x3850 with "pci=use_crs" to make hot-plug work, even though ACPI
> tells us everything we need to know. That's backwards.
>
> We shouldn't need an option to tell Linux that the firmware is
> trustworthy. We should have an option to *ignore* it for the times
> when we trip over something broken and haven't figured out a way to
> work around it yet.

Sorry, I am behind on my email and just noticed this.

When I posted the patches to add "pci=use_crs" it was only
needed to enable PCI hotplug on a subset of our systems.
At that time it was not apparent that others were interested.
I was also concerned that real or anticipated breakage on
on other systems might delay or prevent acceptance.

As long as there is an option to disable it I am also in
favor of trying to make it the default.

Thanks!

Gary

--
Gary Hade
System x Enablement
IBM Linux Technology Center
503-578-4503 IBM T/L: 775-4503
garyhade@us.ibm.com