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Date: Mon, 24 Jun 2013 15:10:20 +0300
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] RFC kvm irqfd: add directly mapped MSI IRQ
 support
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To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Anthony Liguori <aliguori@us.ibm.com>, Alexey Kardashevskiy <aik@ozlabs.ru>, qemu-devel@nongnu.org, Alexander Graf <agraf@suse.de>, qemu-trivial@nongnu.org, Alex Williamson <alex.williamson@redhat.com>, qemu-ppc@nongnu.org, Paolo Bonzini <pbonzini@redhat.com>, Paul Mackerras <paulus@samba.org>, David Gibson <david@gibson.dropbear.id.au>

On Mon, Jun 24, 2013 at 07:36:25AM +1000, Benjamin Herrenschmidt wrote:
> On Sun, 2013-06-23 at 17:07 +0300, Michael S. Tsirkin wrote:
> > Yes I think that's fine really.
> > 
> > Basically devices all speak MSIMessage as they should -
> > this is what the PCI spec says.        
> > On all normal systems guests also speak MSIMessage so
> > the API which uses these makes sense for kvm.
> > Except, ppc architecture in its wisdom decided to hide this
> > in firmware.  QEMU does not have firmware so the translation
> > has to be maintained in QEMU powerpc code.
> 
> It is still not enough. There is nothing that says that an MSI
> address/message is unique. On pseries (among others I'm sure), this is a
> per-host-bridge concept since the MSIs are decoded by the PHB and turned
> into standard fabric interrupts there.
> 
> So at least the bus needs to be passed as well.
> 
> Cheers,
> Ben.

If passing bus (or dma context, etc)
turns out to actually be helpful, why not.

-- 
MST