Re: [PATCH] xen/pci: make bus notifier handler return sane values

[George Dunlap <george.dunlap@citrix.com>]

On Wed, 2011-08-24 at 21:42 +0100, Konrad Rzeszutek Wilk wrote:
> > Requiring the PCI device to be known to Xen to be able to use MSI is
> > an implementation detail of the hypervisor. And in fact I had a patch
> > to remove the call to pci_get_pdev() from map_domain_pirq() (since
> > setup_msi_irq() doesn't really consume this parameter). This got made
> > impossible to do (at least for the moment) with George's
> > 23753:2e0cf9428554 (and later on the device is getting looked up by
> > __pci_enable_msi{,x}() anyway, but even that is an implementation
> > choice, not a hard requirement afaict).

The device has to be known to Xen in order to do proper interrupt
remapping, does it not?  At least if the AMD per-device interrupt
remapping tables.

I suppose if you really wanted to, we could refactor the code so that
the time Xen needed to know devices for IRQs coincided exactly with when
Xen needs to know devices for IOMMUs.  I don't understand the motivation
for such a requirement yet.

 -George