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

[Joerg Roedel <joro-zLv9SwRftAIdnm+yROfE0A@public.gmane.org>]

On Thu, Jun 20, 2013 at 09:44:51AM -0600, Alex Williamson wrote:
> 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:
> > > +	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.

It is simple, but it is still a heuristic that may fail at some point,
no?

> 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,

I think implementing such a list is much safer.

Bjorn, why didn't you like that idea?


	Joerg