Re: [Qemu-devel] [PATCH v2] vfio/igd: handle q35 machine type

[Gerd Hoffmann <kraxel@redhat.com>]

  Hi,

> > q35 already has a isa bridge @ 1f.0, and it's not a dummy device but
> > emulates the ich9 lpc.  Just overwriting the identity of that device
> > isn't a good idea I think.
> 
> It's not a good idea in practice or in theory?  It's exactly what we're
> proposing to do for the host bridge.

We don't change the pci ids for the host bridge.  It's still a
i440fx/q35 host bridge, only the subsystem ID is changed (although I'm
sometimes wondering why), and the gfx registers added of course.

> Do we know for certain that any of
> the emulated ich9 registers do not align with newer chipsets?

See drivers/mfd/lpc_ich.c (lpc_chipset_info array).

Lots of different versions exist for GPIO wiring.  Which probably isn't
that much of a problem as I think we don't emulate gpio.

For iTCO there are tree different versions too, and we *do* emulate
that.

> It seems
> quite limiting of igd assignment on q35 VMs if we're going to remove
> collateral device modification.  Should we only claim "legacy" igd
> support on 440FX and support only universal passthrough on q35?  Thanks,

I'll go test this a bit more.  Possibly we can drop the whole lpc
tweaking.  At least when looking at the linux driver code it doesn't
seem to be very important.

cheers,
  Gerd