Re: [Qemu-devel] device assignment for embedded Power

[Paul Brook <paul@codesourcery.com>]

> > irq[0].guest_irq = "10"
> > 
> > This should be independent of anything to do with device tree.  This
> > would be useful for x86 too to assign platform devices (like the HPET).
> 
> That's fine, as long as there's something layered on top of it for the case
> where we do want to reference something in the device tree.
> 
> However, we'll need to address the question of what it means to say "irq
> 10" -- outside of PC-land there often isn't a global IRQ numberspace that
> isn't a fiction created by some software layer.  Addressing this is one of
> the device tree's strengths.

That's an entirely separate problem, thoug probably a prerequisite.

Basically you should start by implementing full emulation of a device with 
similar characteristics to the one you want to passthrough.

Then fix whatever is needed to allow the user to contol instantiation of those 
devices. This almost certainly means using the -device commandline option.  
This currently only works for a fairly simple subset of devices (approximately 
PCI and USB), so you'll probably need to fix/implement the missing bits.  To 
do this you'll probably need to do some work on the various bits of the qdev 
relating to linking devices together.  See recent discussion about sockets in 
the "basic support for composing sysbus devices" thread.

To expose this to the guest you'll probably also need to implement some form 
of dynamic device tree assembly/manipulation.  Not strictly necessary (we can 
require the user supply a complete device tree that matches whatever devices 
they've configured), but probably highly desirable.

Once you've done all the above, host device passthrough should be relatively 
straightforward.  Just replace the emulation bits in the above device with 
code that pokes at a real device via the relevant kernel API.

Paul