Re: [Qemu-devel] [PATCH 0/4] QOM'ify work for ppc

[David Gibson]

On Wed, Jan 04, 2017 at 05:04:02PM +0000, Peter Maydell wrote:
> On 4 January 2017 at 03:28, David Gibson <address@hidden> wrote:
> > On Tue, Jan 03, 2017 at 10:02:21PM +0800, 赵小强 wrote:
> >> Hi，david：
> >>
> >>    To my understanding，what must be put in the realize function  is
> >>    code which depends on property values. What's the benefit of
> >>    moving memory region initialization into realize function?  I can
> >>    not figure out, can you make some explanations?
> >
> > If nothing else it's better in realize() for consistency with other
> > devices.
> 
> I'm not sure we're terribly consistent at all, really. My understanding
> was about the same as 赵小强 -- put stuff in init unless it has to
> go in realize because it depends on properties or might fail or
> has permanent effects on the simulation.
> Lots of existing devices do memory_region_init* calls in
> their init functions.
> We should probably write down our preferences somewhere, perhaps
> http://wiki.qemu.org/Documentation/QOMConventions
> 
> > I'm not familiar enough with the details to be sure, but I also think
> > it's not safe in instance_init.  Once memory regions are registered,
> > the device can potentially interact with other devices in the virtual
> > machine.  realize() is sequenced to expect that, instance_init is not.
> 
> Hmm, that doesn't sound right to me. The other devices will only
> interact with the memory regions when the calling code has
> finished doing the create/realize/map memory regions sequence --
> an MR on its own doesn't do anything unless somebody maps it into
> an address space.

Huh.  Ok, I guess I was wrong.

Alright, 赵小强, feel free to repost addressing just the other
comments and I'll merge.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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