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Re: [Qemu-devel] [PATCH V2 0/4] hw/pcie: Multi-root support for Q35


From: Marcel Apfelbaum
Subject: Re: [Qemu-devel] [PATCH V2 0/4] hw/pcie: Multi-root support for Q35
Date: Mon, 16 Nov 2015 12:39:45 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0

On 11/16/2015 12:37 PM, Michael S. Tsirkin wrote:
On Mon, Nov 16, 2015 at 12:34:11PM +0200, Marcel Apfelbaum wrote:
On 11/16/2015 12:11 PM, Paolo Bonzini wrote:


On 16/11/2015 11:10, Marcel Apfelbaum wrote:
What would you lose?  Hotplug?

Without the bridge? Yes. However the user can add it manually the
pci-bridge and have it anyway.

Ok, I guess that's more or less acceptable.  It's still ugly however, to
the point that I wonder if we should rename the device and call the old
one a failed experiment.


I guess we can rename the pxb to extra-root or something, but in this way
will have a deprecated/duplicated device to support and kill in the future.

Why not use the compat property as it is?
Again, the command line *remains* the same, the difference is where the
devices associated with the pxb will land: on the secondary bus (for QEMU < 2.5)
or on the root bus itself (QEMU >= 2.5).

I know is guest visible, but the guest will see one of them depending on the 
machine type.

Regarding the splitting of pxb into 2 devices (pci/pcie), I have nothing 
against it,
but because the implementation is *exactly* the same I think we should gain more
by maintaining one device.


Thanks,
Marcel

Yes, I think you want a new "pci-extender" device which is just the extender.
Then existing pxb will create both it and the bridge behind it.
Maybe creating pxb which is extender+bridge was a mistake, I don't know,
but we shipped it in QEMU so we support it.

OK, but this device will be both pci/pcie,  depending on the machine type right?
No need to split it too?

Thanks,
Marcel




Paolo

I wanted to get rid of the internal pci-bridge as a default, and this
is why pxb and pxb-pcie are he same device now (except bus type)




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