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Re: [Xen-devel] [RFC][PATCH] gpu:drm:i915:intel_detect_pch: back to check devfn instead of check class type

On 2014/6/20 20:48, Paolo Bonzini wrote:
Il 19/06/2014 11:53, Tiejun Chen ha scritto:
so this mean that isa bridge is still represented with Dev31:Func0
like the native OS. Furthermore, currently we're pushing VGA
passthrough support into qemu upstream, and with some discussion,
we wouldn't set the bridge class type and just expose this devfn.

Even this is not really optimal.  It just happens to work just because
QEMU's machine is currently a PCI machine with the ISA bridge on 00:01.0.

As soon as you'll try doing integrated graphics passthrough on a PCIe
machine type (such as QEMU's "-M q35") things will break down just as

Sorry, I can't understand why this is related to the ISA bridge, 00:01.0 or even other PCIe machine type.

In virtualized case we always need to create this ISA bridge as a devfn, 00:15.0, work for the i915 driver to support IGD passthrough.

In qemu-xen-traditional, this ISA bridge is already created as follows:

1> We set this ISA type explicitly;
2> We register that as 00:15.0.

In qemu-upstream, as you commented we can't create this as a ISA class type explicitly. So we compromise by faking this ISA bridge without ISA class type setting (as I recall you already said this way is slightly better). Maybe we will figure better way in the future. But anyway, this is always registered as 00:15.0, right? So I think the i915 driver can go back to probe the devfn like the native environment.

If I'm wrong please correct me.


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