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Re: [Qemu-devel] Memory API: handling unassigned physical memory

From: Avi Kivity
Subject: Re: [Qemu-devel] Memory API: handling unassigned physical memory
Date: Tue, 01 May 2012 17:09:07 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:11.0) Gecko/20120329 Thunderbird/11.0.1

On 05/01/2012 04:50 PM, Anthony Liguori wrote:
> On 05/01/2012 08:01 AM, Avi Kivity wrote:
>> On 05/01/2012 03:49 PM, Peter Maydell wrote:
>>> On 1 May 2012 13:48, Avi Kivity<address@hidden>  wrote:
>>>> On 05/01/2012 03:43 PM, Peter Maydell wrote:
>>>>> On 1 May 2012 13:42, Avi Kivity<address@hidden>  wrote:
>>>>>> sysbus should just die.
>>>>> Totally agreed. It's not going to go quietly though...
>>>> Not if you keep suggesting workarounds when I tell unsuspecting
>>>> developers to qomify their devices.
>>> When QOM supports (1) exporting gpio signals and
> This is trivial.  It'll come in as soon as 1.2 opens up.  If folks
> want to start working on a branch with it:
> https://github.com/aliguori/qemu/tree/qom-pin.4
>>> (2) exporting memory regions, then it will be providing the
>>> main things that sysbus provides.
> This is a little tricky.  Here's the problems I've encountered so far:
> a) A lot of devices need the equivalent of it_shift.  it_shift affects
> how addresses are decoded and the size of the memory region.  it_shift
> usually needs to be a device property.
> Since we need to know the size of the memory region to initialize it,
> we need to know the value of it_shift before we can initialize it
> which means we have to delay the initialization of the mmemory region
> until realize.
> I think a nice fix would be to make it_shift as memory region mutator
> and allow it to be set after initialization.

Indeed I wanted to make it_shift as part of the memory core.  But a
mutator?  It doesn't change in real hardware, so this looks artificial. 
So far all mutators really change at runtime.

What is the problem with delaying region initialization until realize?

> b) There's some duplication in MemoryRegions with respect to QOM. 
> Memory regions want to have a name but with QOM they'll be addressable
> via a path.  I go back and forth about how aggressively we want to
> refactor MemoryRegions.

These days region names are purely for debugging.  The ABI bit was moved
to a separate function.

error compiling committee.c: too many arguments to function

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