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Subject: Re: [Qemu-devel] Re: [PATCH 15/15] Implement the bus structure for
	PAPR virtual IO
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
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Date: Sun, 13 Feb 2011 10:17:34 -0600
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To: Alexander Graf <agraf@suse.de>
Cc: Blue Swirl <blauwirbel@gmail.com>, Paul Mackerras <paulus@samba.org>, "qemu-devel@nongnu.org List" <qemu-devel@nongnu.org>, anton@samba.org, David Gibson <david@gibson.dropbear.id.au>

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.