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Date: Thu, 12 May 2016 12:43:06 +0800
From: Peter Xu <peterx@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] pci: fix requester id to be the one on
 root bus
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To: Alex Williamson <alex.williamson@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>, qemu-devel@nongnu.org, pbonzini@redhat.com, jan.kiszka@web.de, rkrcmar@redhat.com

On Wed, May 11, 2016 at 09:22:03PM -0600, Alex Williamson wrote:
[...]
> PCI Express to PCI/PCI-X Bridge Specification rev 1.0
> 2.3 Assignment of Requester ID and Tag by the Bridge
> 
> PCIe-to-PCI bridges assign a requester ID composed of the secondary bus
> number with devfn = 0.  Although often on real hardware, the root
> complex PCI bridge uses the actual bridge requester ID even though
> it's actually a PCIe bridge.  Linux assume that if a bridge has a PCIe
> capability with type PCIe-to-PCI/X bridge we use the secondary bus
> requester ID, if it has a PCIe capability with type PCI/X-to-PCIe, we
> use the bridge requester ID.  If it does not have a PCIe capability we
> use the bridge ID except for a few quirked devices known to use the
> secondary bus ID.  Yay standards!  Thanks,

Thanks Alex!

I have found pci and pci-to-pci bridge specs, which seems useful to
me.  However, I still cannot find pcie-to-pci bridge spec online (as
you have mentioned above).  Is that only for registered users?

-- peterx