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

[Anthony Liguori <anthony@codemonkey.ws>]

On 06/30/2011 07:58 PM, Benjamin Herrenschmidt wrote:
> On Thu, 2011-06-30 at 15:59 +0000, Yoder Stuart-B08248 wrote:
>>     This avoids needing to pass the host device tree, but could
>>     get awkward-- the i2c example above is very simple, some device
>>     nodes are very large with a complex hierarchy of subnodes and
>>     could be hundreds of lines of text to represent a single
>>     node.
>>
>> It gets more complicated...
>
>
> So, from a qemu command line perspective, all you should have to do is
> pass qemu the device-tree -path- to the device you want to pass-trough
> (you may support passing a full hierarchy here).

I agree in principle but I think it should be done in a slightly 
different way.

I think we ought to support composing a device by passthrough.  For 
instance, something like:

[physical-device "mydev"]
region[0].file = "/dev/mem"
region[0].guest_address = "0x42232000"
region[0].file_offset = "0x23423400"
region[0].size = "4096"
irq[0].guest_irq = "10"
irq[0].host_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).

I think there should be a separate mechanism to manipulate the guest 
device tree, just like there are mechanisms to manipulate the guest's 
ACPI tables.

Given these two mechanisms, there should be a simple command line like 
Ben has suggested that just takes a host device tree path and Just 
Works.  It really is just a convenience interface though.

With raw mechanisms like I described above, it would give you the 
flexibility to pass through a device with a modified host tree fragment 
without having an overly complicated command line interface for the more 
common case.

Regards,

Anthony Liguori