Re: [Qemu-devel] [PATCH v3 2/5] hw/pci: introduce pcie-pci-bridge device

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Aug 01, 2017 at 06:45:13PM +0300, Marcel Apfelbaum wrote:
> On 01/08/2017 18:32, Michael S. Tsirkin wrote:
> > On Mon, Jul 31, 2017 at 09:40:41PM +0300, Alexander Bezzubikov wrote:
> > > > > +typedef struct PCIEPCIBridge {
> > > > > +    /*< private >*/
> > > > > +    PCIBridge parent_obj;
> > > > > +
> > > > > +    bool msi_enable;
> > > > 
> > > > 
> > > > Please rename the msi_enable property to "msi" in order
> > > > to be aligned with the existent PCIBridgeDev and
> > > > consider making it OnOffAuto for the same reason.
> > > > (I am not sure about the last part though, we have
> > > >   no meaning for "auto" here)
> > > > 
> > > 
> > > Agreed about "msi", but OnOffAuto looks weird to me
> > > as we always want MSI to be enabled.
> > 
> 
> Hi Michael,
> 
> > Why even have a property then? Can't you enable it unconditionally?
> > 
> 
> Because of a current bug in Linux kernel:
>    https://www.spinics.net/lists/linux-pci/msg63052.html
> msi will not work until the patch is merged. Even when
> it will be merged, not all linux kernels will contain the patch.

You should Cc stable to make sure they all gain it eventually.

> Disabling msi is a workaround for the above case.
> 
> Thanks,
> Marcel

Really enabling MSI without bus master is a bug that I'm not 100% sure
it even worth working around. But I guess it's not too bad to have a
work-around given it's this simple.

-- 
MST