linux-kernel - Re: [PATCH] x86/pci: do assign root bus res if

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Date:	Mon, 27 Apr 2009 12:53:42 -0700
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	Bjorn Helgaas <bjorn.helgaas@...com>
Cc:	Yinghai Lu <yinghai@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-pci@...r.kernel.org, Gary Hade <garyhade@...ibm.com>,
	Alex Chiang <achiang@...com>, linux-acpi@...r.kernel.org,
	Matthew Wilcox <matthew@....cx>
Subject: Re: [PATCH] x86/pci: do assign root bus res if _CRS is used

On Mon, 27 Apr 2009 13:44:01 -0600
Bjorn Helgaas <bjorn.helgaas@...com> 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@...nel.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.

Well, we could try using _CRS by default, but like many things ACPI we
can probably only trust firmwares after a certain date (i.e. the date
when Windows started relying on the data being correct in order to
boot).  Do we have a good cutoff for that?  Or should we try generally
enabling it early in 2.6.31 to see what happens?

-- 
Jesse Barnes, Intel Open Source Technology Center
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