RE: [Xen-devel] [PATCH 1/5] Add MSI support to XEN

["Shan, Haitao" <haitao.shan@xxxxxxxxx>]

>> From: Keir Fraser [mailto:keir.fraser@xxxxxxxxxxxxx]
>> Sent: 2008年3月28日 17:33
>> 
>> On 28/3/08 09:23, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:
>> 
>>> I think the reverse. :-) Here IRQ is just a namespace which is
>>> allocatable and not bound to platform hard-wired logic. Each MSI
>>> just requires one IRQ placeholder to gear to evtchn core with the
>>> latter on top of IRQ name- space. However GSI or ISA IRQ more
>>> indicates platform attribute which doesn't fit the purpose here,
>>> though GSI can be also tweaked in some version of Linux kernel.
>> 
>> I don't understand you. Do you mean *PIRQ* is just a namespace which
>> is allocatable? I fully agree with that. I was talking about the
>> MAO_IRQ_TYPE_IRQ binding type -- here I believe 'IRQ' does
>> refer to a real
>> platform resource, but 'IRQ' is not a well-defined
>> architectural namespace
>> like 'GSI' or 'ISA IRQ'. So the interface should be fixed imo.
> 
> Oh, I jumped in too early. Sorry and you're right.
I will change that name.

> 
>> 
>>> This should work, and may solve the issue Yunhong described in
>>> another mail by giving Xen ability to mask device directly upon
>>> spurious interrupts. And... seems like less change to Linux code?
>>> The only concern is how complex the interface may finally go,
>>> and in this case Xen still needs to sync PCI config space access
>>> for port I/O style.
>> 
>> Yes, the synchronisation is pretty easy though. We just have
>> to add a layer
>> of emulation to PV guest accesses to 0xcf8/0xcfc.
> 
> Yes, a small tricky however is, the owner vcpu may be scheduled
> out between 0xcf8 and 0xcfc access, when another pcpu is trying
> to access PCI config space like masking MSI within do_IRQ...
> Maybe Xen need to emulate 0xcf8/0xcfc pair without return to
> guest in the middle. :-)
Can we add hypercall to combine the two-time access to one?

> 
> Thanks,
> Kevin

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