[libvirt] [PATCH 4/3] conf: restrict expander buses to connect only to a root bus

[Andrea Bolognani]

On Tue, 2016-08-09 at 11:59 -0400, Laine Stump wrote:
> > One thing that's not quite clear to me about pcie-expander-bus:
> > according to the code and comment, it has a single slot that
> > can accomodate either a pcie-root-port or a dmi-to-pci-bridge.
> > 
> > It seems like that would limit its usefulness quite a lot...
> > I would expect at least a pcie-switch-upstream-port to be
> > usable as well. Marcel, can you confirm either way?
> 
> You can't plug a pcie-switch-upstream-port directly into a pcie-expander 
> bus (see https://bugzilla.redhat.com/show_bug.cgi?id=1361172 which was 
> the subject of patch 2)
> 
> You can however plug in a pcie-root-port, and then connect a 
> pcie-switch-upstream-port into the pcie-root-port. (and then of course 
> plug a bunch of pcie-switch-downstream-ports into the upstream-port, and 
> devices into the downstream ports).

I see. That's a bit unfortunate, I guess, but at least it's
not entirely pointless :)

> So does this get ACK with the changes/explanations above? Or do you want 
> me to re-send it?

https://i.imgflip.com/18o30w.jpg

-- 
Andrea Bolognani / Red Hat / Virtualization