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

[David Gibson]

On Thu, Jan 05, 2017 at 08:53:07AM +0800, 赵小强 wrote:
> Ok！
> 
> Just one more comment：
> After check the code flow, It's clear that the initialized memory
> region must be add to address space by calling
> memory_region_add_subregion in platform code before it can be
> accessed.

Yes.. but I don't see how that's relevant to the discussion at hand.

> 
> Best wishes ！
> 
> > 在 2017年1月5日，08:20，David Gibson <address@hidden> 写道：
> > 
> >> 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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