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Re: [Qemu-devel] [PATCH v2 12/13] intel_iommu: ioapic: IR support for em

From: Peter Xu
Subject: Re: [Qemu-devel] [PATCH v2 12/13] intel_iommu: ioapic: IR support for emulated IOAPIC
Date: Thu, 14 Apr 2016 10:46:45 +0800
User-agent: Mutt/1.5.24 (2015-08-30)

On Wed, Apr 13, 2016 at 07:44:54AM -0700, Jan Kiszka wrote:
> > One thing I am curious about: I see that in vtd spec
> > 
> > "RTE bits 10:8 is programmed to 000b (Fixed) to force the SHV
> > (SubHandle Valid) field as Clear in the interrupt address
> > generated."
> > 
> > So... In real IOMMU hardwares, IOAPIC interrupt will finally be
> > translated to MSI as well? am I understanding it correctly?
> It will be translated into something that the IR unit can receive -
> whatever that is technically. Logically, there is no difference to MSIs
> received from PCI devices.

Ok. I see there are still differences between IOAPIC and MSI, e.g.,
for IOAPIC entries, it has "Interrupt Input Pin Polarity", which is
bit 13 of the entry, to show whether 1 or 0 is taken as assertion
for level-triggered interrupts. While in MSI, I assume assertion
will be 1 always. Can I take it as "obsolete" and we will never use

If to take IOAPIC entries as MSI messages, all these extra bits will
be dropped (it's dropped in ioapic_service() already, but not sure
whether we will pick them up in the future).

> > 
> > Btw, if to use the way you suggested, the patch content would
> > possibly be very alike the one you and Rita has posted, which is:
> > 
> > https://lists.gnu.org/archive/html/qemu-devel/2016-03/msg01933.html
> > 
> > I will only pick up those lines I needed in supporting IOAPIC. If
> > so, do you mind I add your s-o-b as well above mine (maybe add
> > Rita's too)?
> If a patch is almost identical, add your [Peter: my changes...] line and
> your signed of to it. If it is more modified, claim authorship and just
> refer to the original authors in the commit log.

Ok. Thanks.

-- peterx

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