linux-kernel - Re: [tip:x86/pci] x86, pci: Ignore any PCI BARs that match an HPET we already know about

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Date:	Wed, 22 Sep 2010 16:41:35 -0600
From:	Bjorn Helgaas <bjorn.helgaas@...com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	simon@...e.lp0.eu, tglx@...utronix.de, hpa@...ux.intel.com,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/pci] x86, pci: Ignore any PCI BARs that match an HPET we already know about

On Wednesday, September 22, 2010 03:48:44 pm Yinghai Lu wrote:
> On 09/22/2010 02:22 PM, tip-bot for Bjorn Helgaas wrote:
> > Commit-ID:  e72a6c8f7ac715a9cdb473afbc30743348d0a1e2
> > Gitweb:     http://git.kernel.org/tip/e72a6c8f7ac715a9cdb473afbc30743348d0a1e2
> > Author:     Bjorn Helgaas <bjorn.helgaas@...com>
> > AuthorDate: Wed, 22 Sep 2010 14:15:47 -0600
> > Committer:  H. Peter Anvin <hpa@...ux.intel.com>
> > CommitDate: Wed, 22 Sep 2010 13:29:39 -0700
> > 
> > x86, pci: Ignore any PCI BARs that match an HPET we already know about
> > 
> > We often discover the HPET early, via the static ACPI HPET table,
> > before enumerating PCI devices.  If the HPET is implemented as a PCI
> > function, we will discover it again during PCI device enumeration.  We
> > must ignore the PCI function so we don't inadvertently move it out
> > from under the driver.
> > 
> > I think it's better to ignore *any* PCI BAR that matches a previously
> > discovered HPET; that way we don't need platform-specific knowledge,
> > and we won't have to add more quirks for future machines.
> > 
> > This is for a regression from 2.6.34, but the reporter has been
> > unable to test it yet.
> > 
> > [ hpa: if this fixes the regression, it should be promoted to x86/urgent ]
> > 
> > Reference: https://bugzilla.kernel.org/show_bug.cgi?id=18482
> > Reported-by: Simon Arlott <simon@...e.lp0.eu>
> > Signed-off-by: Bjorn Helgaas <bjorn.helgaas@...com>
> > LKML-Reference: <20100922201547.3197.33702.stgit@....kio>
> > Signed-off-by: H. Peter Anvin <hpa@...ux.intel.com>
> > ---
> >  arch/x86/kernel/quirks.c |   21 +++++++++++++++++++++
> >  arch/x86/pci/fixup.c     |   28 ----------------------------
> >  2 files changed, 21 insertions(+), 28 deletions(-)
> > 
> > diff --git a/arch/x86/kernel/quirks.c b/arch/x86/kernel/quirks.c
> > index 939b9e9..99a7d4b 100644
> > --- a/arch/x86/kernel/quirks.c
> > +++ b/arch/x86/kernel/quirks.c
> > @@ -507,6 +507,27 @@ static void force_disable_hpet_msi(struct pci_dev *unused)
> >  DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_ATI, PCI_DEVICE_ID_ATI_SBX00_SMBUS,
> >  			 force_disable_hpet_msi);
> >  
> > +static void disable_pci_hpet(struct pci_dev *dev)
> > +{
> > +	int i;
> > +
> > +	if (!hpet_address)
> > +		return;
> > +
> > +	for (i = 0; i < 6; i++) {
> > +		struct resource *res = &dev->resource[i];
> > +
> > +		if (resource_type(res) == IORESOURCE_MEM &&
> > +		    res->start == hpet_address) {
> > +			dev_info(&dev->dev, "BAR %d: %pR is an HPET we found earlier; ignoring this BAR\n",
> > +				 i, res);
> > +			res->flags = 0;
> > +			res->start = 0;
> > +			res->end = 0;
> > +		}
> > +	}
> > +}
> 
> It seems there is some problem here:
> 
> hpet_res is inserted to resource with late_initcall().
> so if you don't touch that hpet address in bar and not put in the resource.
> kernel could allocate that address to other devices that doesn't get resource from BIOS.

Hmm, yes, that's a problem.  Let me look into it tomorrow; maybe we
can do something like setting IORESOURCE_PCI_FIXED instead of just
clearing out the resource.

Bjorn
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