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Re: [Xen-devel] [v5][PATCH 0/5] xen: add Intel IGD passthrough support

On 2014/6/25 18:21, Michael S. Tsirkin wrote:
On Wed, Jun 25, 2014 at 06:06:50PM +0800, Chen, Tiejun wrote:
On 2014/6/25 17:59, Paolo Bonzini wrote:
Il 25/06/2014 11:55, Michael S. Tsirkin ha scritto:
You're saying we will reserve a free BAR to address those
information to
expose to guest, but which device does this free BAR belong to? The
device? Or PCH/MCH?

If you just want to pass a couple of IDs, then don't, it's a waste.
But I still don't know what problem you are trying to solve,
looking at guest driver did not help.

It's not just a couple of IDs, it's also random fields of the MCH
configuration space.  Grep drivers/gpu/drm/i915 for bridge_dev.


No, we're not pointing the bridge_dev here, which is a host bridge at

Here it should be a ISA bridge at 00:1f.0. Please see intel_detect_pch() to
know why we need this.


So what if you dont?

         if (!pch)
                 DRM_DEBUG_KMS("No PCH found.\n");

Is that all? Seems harmless enough.

I don't read the whole driver completely so I don't know now. I guess the driver may go other live path even without this setting in a live, or this is a real bug to this driver on Intel platform.

But anyway, I think we should guarantee the driver work under the same configuration as the native in the passthrough case.


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