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From: Gerd Hoffmann <kraxel@redhat.com>
Date: Fri, 23 Jan 2015 14:53:27 +0100
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Subject: Re: [Qemu-devel] [RfC PATCH] virtio-pci: place msix regions in
	modern virtio bar
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: qemu-devel@nongnu.org, Anthony Liguori <aliguori@amazon.com>

  Hi,

> I wanted to make the modern BAR prefetcheable, so it can
> be a full 64-bit one,

It's not the case right now though, the two bars have identical
attributes, and there is plenty of unused space in the modern virtio
bar ...

> this is impossible with the MSI-X
> BAR.

What exactly is impossible?  msi-x being in a 64bit bar?  msi-x being in
a prefetchable bar?  Also why the bar needs to be prefetchable to be
64bit bit?

xhci looks this way right now:

00:0f.0 USB controller: NEC Corporation uPD720200 USB 3.0 Host
Controller (rev 03) (prog-if 30 [XHCI])
	Subsystem: Red Hat, Inc QEMU Virtual Machine
	Physical Slot: 15
	Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr-
Stepping- SERR+ FastB2B- DisINTx+
	Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort-
<MAbort- >SERR- <PERR- INTx-
	Latency: 0, Cache Line Size: 64 bytes
	Interrupt: pin A routed to IRQ 10
	Region 0: Memory at febd0000 (64-bit, non-prefetchable) [size=16K]
	Capabilities: [90] MSI-X: Enable+ Count=16 Masked-
		Vector table: BAR=0 offset=00003000
		PBA: BAR=0 offset=00003800
	Capabilities: [70] MSI: Enable- Count=1/16 Maskable- 64bit+
		Address: 0000000000000000  Data: 0000
	Kernel driver in use: xhci_hcd

Which works just fine even with msi-x in a 64-bit (non-prefetchable)
bar, but maybe just by pure luck?  Also seabios wouldn't map the bar
above 4G.

cheers,
  Gerd