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Re: [Xen-users] Marvell, IOMMU/VT-d, and pci-phantom

On Fri, 2013-06-28 at 14:59 +0100, Jan Beulich wrote:
> > It seems to me from peering at the docs that one of those (probably the
> > second) ought to be correct, but I'm not sure what the <stride>
> > parameter is supposed to be, although I suspect it ought to be non-zero.
> Exactly (at least to me "stride" can't possibly mean something that
> might be zero, except perhaps as a disable indicator).


>  So
> pci-phantom=06:00,1
> should do, provided this is a single-function device.

So what does stride actually mean? To me it suggests every N-th device,
but in that case how do we know how many there are in total?

> > Jan, since you wrote this patch for Marvell devices I suppose you know
> > the right incantation for this bit of hardware?
> The specific hardware doesn't matter, we're basically just overriding
> rwo bits that a device behaving this way should have set in its PCIe
> capability structure (i.e. the resulting behavior is generic).

I'm not 100% convinced that requiring users to understand the PCIe
capability structures here is "fair", but I suppose it is an advanced

Assuming you meant "two" not "rwo", which two bits are they?

> >> and finally, on the off chance I'd glean something useful doing this:
> >> 
> >>    mybox:~$ strings /boot/xen-syms-4.3-unstable | grep -i phantom
> >>    <3>PCI phantom %04x:%02x:%02x.%u
> >>    pci-phantom
> >> 
> >> I even tried this:
> >> 
> >>     /boot/xen-4.3-unstable.gz placeholder pci-phantom=0000:06:00.0
> >> pci-phantom=0000:0a:00.0
> >> 
> >> All to no avail.  I've Googled my smallish head off and I've tried to
> >> scour this list to see if anybody else has been trying out this
> >> option, but I can't seem to find anything.
> Googling is probably of less help here than simply taking a look at
> the function that does the parsing
> (xen/drivers/passthrough/pci.c:parse_phantom_dev()); of course
> I admit this assumes you can at least read C code.
> Jan

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