Re: [Qemu-devel] [PATCH V2 0/4] hw/pcie: Multi-root support for Q35

[Michael S. Tsirkin]

On Mon, Nov 16, 2015 at 12:39:45PM +0200, Marcel Apfelbaum wrote:
> On 11/16/2015 12:37 PM, Michael S. Tsirkin wrote:
> >On Mon, Nov 16, 2015 at 12:34:11PM +0200, Marcel Apfelbaum wrote:
> >>On 11/16/2015 12:11 PM, Paolo Bonzini wrote:
> >>>
> >>>
> >>>On 16/11/2015 11:10, Marcel Apfelbaum wrote:
> >>>>>What would you lose?  Hotplug?
> >>>>
> >>>>Without the bridge? Yes. However the user can add it manually the
> >>>>pci-bridge and have it anyway.
> >>>
> >>>Ok, I guess that's more or less acceptable.  It's still ugly however, to
> >>>the point that I wonder if we should rename the device and call the old
> >>>one a failed experiment.
> >>>
> >>
> >>I guess we can rename the pxb to extra-root or something, but in this way
> >>will have a deprecated/duplicated device to support and kill in the future.
> >>
> >>Why not use the compat property as it is?
> >>Again, the command line *remains* the same, the difference is where the
> >>devices associated with the pxb will land: on the secondary bus (for QEMU < 
> >>2.5)
> >>or on the root bus itself (QEMU >= 2.5).
> >>
> >>I know is guest visible, but the guest will see one of them depending on 
> >>the machine type.
> >>
> >>Regarding the splitting of pxb into 2 devices (pci/pcie), I have nothing 
> >>against it,
> >>but because the implementation is *exactly* the same I think we should gain 
> >>more
> >>by maintaining one device.
> >>
> >>
> >>Thanks,
> >>Marcel
> >
> >Yes, I think you want a new "pci-extender" device which is just the extender.
> >Then existing pxb will create both it and the bridge behind it.
> >Maybe creating pxb which is extender+bridge was a mistake, I don't know,
> >but we shipped it in QEMU so we support it.
> 
> OK, but this device will be both pci/pcie,  depending on the machine type 
> right?
> No need to split it too?
> 
> Thanks,
> Marcel

It's ok to have a single device but I don't like
tying it to a machine type, much.
It's always integrated within a RC, right?
Can you go by the type of the parent device?

> 
> >
> >>
> >>>Paolo
> >>>
> >>>>I wanted to get rid of the internal pci-bridge as a default, and this
> >>>>is why pxb and pxb-pcie are he same device now (except bus type)