Re: [Qemu-devel] Attaching PCI devices to the PCIe root complex

[Paolo Bonzini]

Il 25/09/2013 10:59, Michael S. Tsirkin ha scritto:
>> > I couldn't find on PCIe spec any mention that "Root Complex Integrated 
>> > EndPoint"
>> > must be PCIe. But, from spec 1.3.2.3:
>> > - A Root Complex Integrated Endpoint must not require I/O resources 
>> > claimed through BAR(s).
>> > - A Root Complex Integrated Endpoint must not generate I/O Requests.
>> > - A Root Complex Integrated Endpoint is required to support MSI or MSI-X 
>> > or both if an
>> > interrupt resource is requested.
> Heh PCI-SIG keeps fighting against legacy interrupts and IO.
> But lots of hardware happily ignores these rules.
> And the reason is simple: software does not enforce them.

I think it's "must not require", not "must not have".  So it's the usual
rule that applies to PCIe device, i.e. that they should work even if the
OS doesn't enable the I/O BARs.

Then I have no idea what the I/O BAR in i915 is for, and whether the
device can be used without that BAR.

Paolo