Re: [Qemu-devel] [PATCH 0/2] add check for PCIe root ports and downstream ports

[Gonglei (Arei)]

Hi,

> -----Original Message-----
> From: Michael S. Tsirkin [mailto:address@hidden
> On Tue, Aug 19, 2014 at 09:08:25PM +0800, address@hidden wrote:
> > From: Gonglei <address@hidden>
> >
> > Root ports and downstream ports of switches are the hot
> > pluggable ports in a PCI Express hierarchy.
> > PCI Express supports chip-to-chip interconnect, a PCIe link can
> > only connect one pci device/Switch/EndPoint or PCI-bridge.
> >
> > 7.3. Configuration Transaction Rules (PCI Express specification 3.0)
> > 7.3.1. Device Number
> >
> > Downstream Ports that do not have ARI Forwarding enabled must
> > associate only Device 0 with the device attached to the Logical Bus
> > representing the Link from the Port.
> >
> > Right now, ARI Forwarding dose not support. So, only slot 0 is
> > supported, regardless of hotplug or coldplug.
> 
> I'd rather we added ARI support in bridges (if that's
> what you mean) than APIs for the sole purpose of
> disabling functionality we'll want to re-enable later.
> 
Yes, we can add ARI support. But I don't think this check is 
superfluous. Because if some bridges don't enable this function,
we still need this check, just add more check conditions, such as check 
the bit of ARI capability be set or not.

> We have the beginning of an implementation for ARI (pcie_ari_init).
> 
Thanks for your reminding, MST.

Best regards,
-Gonglei