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Re: [Xen-devel] Re: APIC rework

To: "Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx>
Subject: Re: [Xen-devel] Re: APIC rework
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Tue, 17 Nov 2009 10:51:23 -0800
Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, "Han, Weidong" <weidong.han@xxxxxxxxx>, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
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On 11/17/09 06:17, Zhang, Xiantao wrote:
> Originally, this patch is target to get rid of ioapic changes in dom0. Before 
> this patch, GSI irq should be mapped and setup through dom0 programming 
> ioapic entries, but it depends on using ioapic logic in dom0. And if we 
> remove ioapic logic from dom0,  we need to find new way how to setup GSI irq. 
>  And this patch comes out under this situation.  The idea is from that in Xen 
> the interface MAP_PIRQ_TYPE_MSI is used to build the pirq and irq mapping for 
> MSI IRQ for each domain. Since MSI IRQ can be setup through this hypercall, 
> and I think  we also can leverage the interface MAP_PIRQ_TYPE _GSI to build 
> the mapping for GSI irq. Further analysis showes that this interface is only 
> used for assigning devices to HVM domain in qemu, and I think it should be 
> Okay for dom0 building the mapping between its pirq and irq. One different 
> thing for GSI irq is that more info should be provided in the call, since GSI 
> IRQ has different trigger-mode and polarity (originally it is provided by 
> ioapic write in dom0). Certainly, I also think we need to document the 
> related info, and if you agree to the change, I am happy to add it. 

I don't think there's any need to overload the existing interface
though.  If we're adding new functionality then we can add a new
interface for it (but with luck we can reuse most of the existing code
to implement it).

If you're already considering a "treat this differently" flag in the
argument, then that's a strong pointer that a new interface is warranted.

But also consider the question whether Xen needs to get triggering info
from dom0 at all, or whether it can correctly derive that info from its
own parsing of the relevant tables.


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