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Re: [Qemu-devel] [PATCH v2] vfio/igd: handle q35 machine type
From: |
Gerd Hoffmann |
Subject: |
Re: [Qemu-devel] [PATCH v2] vfio/igd: handle q35 machine type |
Date: |
Wed, 09 Mar 2016 09:03:57 +0100 |
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