Re: [Qemu-devel] Re: [PATCH 15/15] Implement the bus structure for PAPR virtual IO

[Benjamin Herrenschmidt]

On Sun, 2011-02-13 at 13:40 +0100, Alexander Graf wrote:
> 
> We can surely move it to dynamic later on. I think the "proper" way
> would be to populate a qdev bus and have the individual hypercall
> receivers register themselves through -device creations. But Blue
> really is the expert here :).

Why would you want to go through a bus for all hcalls ? (ie including
the ones that aren't device related ?). That doesn't quite "tick" but
I'm sure I'm missing part of the picture here :-)

A simple dispatch table based approach is the most efficient and simple
way to do that (after a switch/case) in my opinion, this is more/less
what we have done internally, with a pair of calls for "modules" to
register hcalls if they need to. The hcalls numbers are fixed and
specified in sPAPR.

BTW. We are still missing in this picture RTAS. I suppose David is still
cleaning up those patches. Basically, we use a 5 instruction trampoline
that calls a private h-call, the RTAS emulation is entirely in qemu.
This has to be done that way for various reasons, but essentially RTAS
under pHyp also more/less turns into private pHyp calls under the hood.
 
Cheers,
Ben.