Re: [Xen-devel] Re: APIC rework

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Wed, Nov 18, 2009 at 11:37:51AM +0800, Zhang, Xiantao wrote:
> Jeremy Fitzhardinge wrote:
> > 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. 
> 
> Agree, and I also don't object to add a similar interface.  
> Since this existing interface is only used for hvm domain before, and  just 
> want to re-use it for dom. 

I am pretty sure it is used for PV domains too. Look in 'xen_create_msi_irq', 
which
extracts the domain that has a PCI device for pass-through and on behalf of that
domain makes the MAP_PIRQ_TYPE_MSI call.

Furthermore, it is also used by Dom0 for MSI devices.

What do you mean by 're-use it for dom'?

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