Re: [Qemu-devel] [v5][PATCH 4/5] xen, gfx passthrough: create host bridge to passthrough

[Chen, Tiejun]

On 2014/6/29 20:14, Michael S. Tsirkin wrote:
> On Sun, Jun 29, 2014 at 03:56:10PM +0800, Chen, Tiejun wrote:
> > On 2014/6/27 19:26, Paolo Bonzini wrote:
> > > Il 27/06/2014 10:34, Chen, Tiejun ha scritto:
> > > > So how to separate this to specific to xen? Or you mean we need to
> > > > create an new machine to address this scenario? But actually this is
> > > > same as xenfv_machine except for these little codes.
> > >
> > > Yes, please create a new machine so that "-M pc" doesn't have any of
> > > these hacks.
> >
> > But regardless of the machine is 'xenfv' or 'pc', we always call
> > pc_init_pci(), then inside, i440fx_init() is always performed. So I think
> > even we create a new machine, shouldn't we still call pc_init_pci()?
> >
> > > Note that "-M xenfv" is obsolete, Xen can now use "-M pc" (i.e. the
> > > default).
> >
> > Yes, Xen can use 'pc'.
> >
> > Thanks
> > Tiejun
>
> You are creating a new machine type where the pci host
> looks like MCH but a bunch of other things are from i440fx.

Anthony,

Any comments to address this in xen case?

Thanks
Tiejun

> I have some doubts about this combination being worth supporting - it
> does not seem useful for anything except xen from the code you posted,
> but maybe you can whittle down the number of places where you poke at
> the host to make it reasonable: I can imagine that, if you are lucky and
> the registers that i915 wants to poke to make it work on real hardware
> happen to fall on top of reserved registers in the i440FX/PIIX3 pci
> bridge.  OTOH it would be much more likely if you just start with
> something that does have MCH, like Q35, or emulate a newer
> machine type.  This is the path that people who wanted
> to boot iOS on QEMU took, and the result is pretty good.
>
> But regardless, this is clearly not a i440fx nor a q35 pc
> so it needs a separate name.