Re: PCIE

["H. Peter Anvin" <hpa@zytor.com>]

Grant Grundler wrote:
> On Sun, May 27, 2007 at 06:03:29PM -0700, Roland Dreier wrote:
> ...
>>  > I can imagine many systems where the cpu simply doesn't have enough
>>  > interrupt pins to uniquely identify every possible MSI interrupt
>>  > source.
>>
>> I have a hard time imagining a PCI host bus controller that converts
>> MSI interrupts back to wire interrupts that go to pins on the CPU.
>> For one thing it would be hard to maintain the guarantee that
>> MSI interrupts can't pass DMAs.
> 
> Whatever converts the MSI back to CPU IRQ pins would have to participate
> in the "cache coherency domain". This would avoid issues around DMA ordering.
> It _could_ be on the same silicon as the PCI Host bus controller as long
> as the above is true.
> 

Also, don't forget that a lot of platforms provide *no* hardware cache
coherency.

	-hpa
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