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Date: Tue, 21 Feb 2012 09:02:59 +0100
From: Gerd Hoffmann <kraxel@redhat.com>
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Subject: Re: [Qemu-devel] [PATCHv2-RFC 2/2] pci: add standard bridge device
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Isaku Yamahata <yamahata@valinux.co.jp>, qemu-devel@nongnu.org, kvm@vger.kernel.org, Avi Kivity <avi@redhat.com>

  Hi,

>> This seems to not support 64bit prefetchable memory windows, at least
>> linux doesn't think it does, lspci looks like this:
>>
>> 00:10.0 PCI bridge: Red Hat, Inc. Device 0001 (prog-if 00 [Normal decode])
[ ... ]
>>         Memory behind bridge: f6000000-f60fffff
>>         Prefetchable memory behind bridge: f8000000-fbffffff

> What in the above tells you that 64 bit windows are not supported?

lspci prints 64bit addresses then, like this:

00:1c.0 PCI bridge: Intel Corporation 82801I (ICH9 Family) PCI Express
Port 1 (rev 03) (prog-if 00 [Normal decode])
[ ... ]
        I/O behind bridge: 00008000-00008fff
        Memory behind bridge: c0000000-c01fffff
        Prefetchable memory behind bridge: 00000000c0200000-00000000c03fffff

> BAR0 is 32 bit non prefetcheable. As far as I can see linux driver
> takes no precautions against access combining that can
> happen with prefetcheable BARs, so non-prefetcheable
> seems safer.

I'm not talking about bar #0, but about the prefetchable memory window
for devices behind the bridge.

cheers,
  Gerd