Re: [Qemu-devel] [PATCH] vfio-pci: Quirk RTL8168 NIC

[Alex Williamson <alex.williamson@redhat.com>]

On Mon, 2014-05-12 at 14:28 -0600, Alex Williamson wrote:
> On Mon, 2014-05-12 at 22:02 +0200, Francois Romieu wrote:
> > Alex Williamson <alex.williamson@redhat.com> :
> > [...]
> > > device MSI will be blocked.  The Linux driver doesn't make use of this
> > > window, so apparently it's not required to make use of MSI-X.  This
> > 
> > It does not really use MSI-X (no RSS).
> 
> Oh right, I looked for code references to the register but didn't notice
> that Linux configures it for MSI, not MSI-X.  In my brief testing I only
> saw that Windows generates interrupts on the first vector, so perhaps
> not much lost without the extra vectors.  I guess it's this patch that
> proves that MSI-X can be configured without this backdoor then.  Do you
> have any insight into why this exists?
> 
> > > quirk makes the device work with the Windows driver that does use this
> > > window for MSI-X, but I certainly cannot recommend this device for
> > > assignment (the Windows 7 driver also constantly pokes PCI config
> > > space).
> > 
> > Do you have some offsets for those ?
> 
> I believe it was 0x80, which is 0x10 off from the PCIe capability, so
> the link control register.  I don't seem to have a log, but I'll
> regenerate one tonight to get the exact sequence (the interface is in
> use right now).

As promised:

vfio: vfio_pci_read_config(0000:05:00.0, @0x4, len=0x2) 507
vfio: vfio_pci_read_config(0000:05:00.0, @0x80, len=0x1) 40
vfio: vfio_pci_read_config(0000:05:00.0, @0x81, len=0x1) 0
vfio: vfio_pci_read_config(0000:05:00.0, @0x80, len=0x1) 40
vfio: vfio_pci_read_config(0000:05:00.0, @0x81, len=0x1) 0
vfio: vfio_pci_read_config(0000:05:00.0, @0x80, len=0x1) 40
vfio: vfio_pci_read_config(0000:05:00.0, @0x81, len=0x1) 0

The 80/81 access may happen asynchronous to the command register access,
sometimes I see 3 sets between the command register access as above,
sometimes 4.

As I mentioned earlier, the PCIe cap is at 0x70:

Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 06)
Subsystem: ASUSTeK Computer Inc. P8P67 and other motherboards
...
Capabilities: [70] Express Endpoint, MSI 01

So the cycle is:

word read from command register: I/O+ Mem+ BusMaster+ DisINTx+ SERR+

byte read from PCIe link control register[0]: CommClk+
byte read from PCIe link control register[1]: nothing

I'll be interested if that means anything to you.  It's not a very high
rate access, the command register access is maybe 1Hz.  Thanks,

Alex