Re: [PATCH v2 1/2] iommu: Quirked PCIe bridge test and search function

[Alex Williamson <alex.williamson@redhat.com>]

On Thu, 2013-06-20 at 15:59 +0200, Joerg Roedel wrote:
> On Tue, May 28, 2013 at 12:40:20PM -0600, Alex Williamson wrote:
> > +bool iommu_pci_is_pcie_bridge(struct pci_dev *pdev)
> > +{
> > +	if (!pdev->subordinate)
> > +		return false;
> > +
> > +	if (pci_is_pcie(pdev))
> > +		return true;
> > +
> > +#ifdef CONFIG_PCI_QUIRKS
> > +	/*
> > +	 * If we're not on the root bus, look one device upstream of the
> > +	 * current device.  If that device is PCIe and is not a PCIe-to-PCI
> > +	 * bridge, then the current device is effectively PCIe as it must
> > +	 * be the PCIe-to-PCI bridge.  This handles several bridges that
> > +	 * violate the PCIe spec by not exposing a PCIe capability:
> > +	 * https://bugzilla.kernel.org/show_bug.cgi?id=44881
> > +	 */
> > +	if (!pci_is_root_bus(pdev->bus)) {
> > +		struct pci_dev *parent = pdev->bus->self;
> > +
> > +		if (pci_is_pcie(parent) &&
> > +		    pci_pcie_type(parent) != PCI_EXP_TYPE_PCI_BRIDGE)
> > +			return true;
> > +	}
> 
> Hmm, that looks a bit dangerous.

How so?  The algorithm seems pretty simple and logical.

>  Do we have a list of PCI
> vendor/device-ids of these broken bridges to match against instead of
> some open-coded heuristics?
> 
> That would probably also help to bring this into the PCI code.

Actually, I believe Bjorn rejected the idea of a fixed list because this
problem is detectable.  He also doesn't want me messing with quirks to
pci_is_pcie() in PCI because he wants a 1:1 relation between that and
having a PCIe capability.  So, I'm stuck and this is where it's ended
up.  Thanks,

Alex