Re: [Qemu-devel] [BUG] virtio-net linux driver fails to probe on MIPS Malta since 'hw/virtio-pci: fix virtio behaviour'

[Marcel Apfelbaum]

On 03/20/2017 05:43 PM, Michael S. Tsirkin wrote:
> On Mon, Mar 20, 2017 at 05:21:22PM +0200, Marcel Apfelbaum wrote:
> > On 03/17/2017 11:57 PM, James Hogan wrote:
> > > Hi,
> > >
> > > I've bisected the following failure of the virtio_net linux v4.10 driver
> > > to probe in QEMU v2.9.0-rc1 emulating a MIPS Malta machine:
> > >
> > > virtio_net virtio0: virtio: device uses modern interface but does not have 
> > > VIRTIO_F_VERSION_1
> > > virtio_net: probe of virtio0 failed with error -22
> > >
> > > To QEMU commit 9a4c0e220d8a ("hw/virtio-pci: fix virtio behaviour").
> > >
> > > It appears that adding ",disable-modern=on,disable-legacy=off" to the
> > > virtio-net -device makes it work again.
> > >
> > > I presume this should really just work out of the box. Any ideas why it
> > > isn't?
> >
> > Hi,
> >
> >
> > This is strange. This commit changes virtio devices from legacy to virtio 
> > "transitional".
> > (your command line changes it to legacy)
> > Linux 4.10 supports virtio modern/transitional (as far as I know) and on QEMU 
> > side
> > there is nothing new.
> >
> > Michael, do you have any idea?
> >
> > Thanks,
> > Marcel
>
> My guess would be firmware mishandling 64 bit BARs - we saw such
> a case on sparc previously. As a result you are probably reading
> all zeroes from features register or something like that.
> Marcel, could you send a patch making the bar 32 bit?
> If that helps we know what the issue is.

Hi James,

Can you please check if the below patch fixes the problem?
Please note it is not a solution.

diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index f9b7244..5b4d429 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -1671,9 +1671,7 @@ static void virtio_pci_device_plugged(DeviceState *d, 
Error **errp)
         }

         pci_register_bar(&proxy->pci_dev, proxy->modern_mem_bar_idx,
-                         PCI_BASE_ADDRESS_SPACE_MEMORY |
-                         PCI_BASE_ADDRESS_MEM_PREFETCH |
-                         PCI_BASE_ADDRESS_MEM_TYPE_64,
+                         PCI_BASE_ADDRESS_SPACE_MEMORY,
                          &proxy->modern_bar);

         proxy->config_cap = virtio_pci_add_mem_cap(proxy, &cfg.cap);


Thanks,
Marcel