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

["Chen, Tiejun" <tiejun.chen@xxxxxxxxx>]

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
> badly.
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.

Thanks
Tiejun

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