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Re: [Xen-devel] [PATCH 2/3] qemu-xen-trad: Correctly expose PCH ISA bridge for IGD passthrough

On Tue, May 21, 2013 at 11:39 PM, G.R. <firemeteor@xxxxxxxxxxxxxxxxxxxxx> wrote:
> It has been a long time, but Pasi reminded me to follow this up.
> Here is my feedback to your concern:
> On Fri, Feb 8, 2013 at 3:51 PM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>>>>> On 07.02.13 at 18:43, "G.R." <firemeteor@xxxxxxxxxxxxxxxxxxxxx> wrote:
>>>> For one I wonder whether this is really _always_ correct. I.e.
>>>> the device at 00:1f.0 always being an ISA bridge. Wouldn't it
>>>> be better to mirror whatever the host device says?
>>> From the Intel driver code, it's looking for an intel ISA bridge.
>> That doesn't mean that it always will be.
> Unless you can 100% simulate the HW, you have to rely on the known
> protocol between driver && HW.
> I agree that they may switch to different protocol some day, but I
> don't think we have any better choice.
>>> So your question would be should it be always at 00:1f.0.
>>> So far it seems that it is.
>> Same thing here. We ought to be careful, or else we risk to
>> introduce issues that pretty hard to locate, debug, and fix.
> Since most (if not all) recent intel chipsets in the market have ISA
> bridge at address 00:1f.0, simulate one at the same address to the
> guest won't be so bad, given the current protocol between driver &&
> HW.
> But I guess your concern is about the hard-coded '00:1f.0' address.
> Yes, I agree that this is not beautiful at all.
> I don't mind changing it to probe the ISA bridge from host. But I'm
> not familiar with qemu at all, could you show me the API to achieve
> this purpose?

if I got no response on the API that I queried for, I would just send
out a patch version that does not touch this part.

> Also, if we really care about doing the 'correct' thing, I think we
> should get rid of the default ISA bridge provided by qemu -- currently
> it requires extra patches to linux i915 driver to work around. Anyway
> to achieve this purpose?

I found one API pci_hide_device() may be helpful for this purpose.
I would like to try out, but still lack of the API to locate specified
device in the bus.
> Thanks,
> Timothy (Rui)

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