Re: [Qemu-devel] Adding memory region without specifying address

[Alexander Graf]

> Am 30.06.2014 um 23:47 schrieb "Stalley, Sean" <address@hidden>:
> 
> 
> 
>> -----Original Message-----
>> From: Alexander Graf [mailto:address@hidden
>> Sent: Monday, June 30, 2014 1:22 PM
>> To: Stalley, Sean; Peter Crosthwaite
>> Cc: address@hidden
>> Subject: Re: [Qemu-devel] Adding memory region without specifying address
>> 
>> 
>>> On 30.06.14 19:53, Stalley, Sean wrote:
>>> Thanks for the quick response! Sorry for my belated reply...
>>> 
>>>> -----Original Message-----
>>>> From: address@hidden
>>>> [mailto:address@hidden On Behalf Of Peter
>>>> Crosthwaite
>>>> Sent: Friday, June 27, 2014 6:26 PM
>>>> To: Stalley, Sean; Alexander Graf
>>>> Cc: address@hidden
>>>> Subject: Re: [Qemu-devel] Adding memory region without specifying
>>>> address
>>>> 
>>>> On Sat, Jun 28, 2014 at 10:29 AM, Stalley, Sean <address@hidden>
>> wrote:
>>>>> Hello All,
>>>>> 
>>>>> 
>>>>> 
>>>>> I am working on building a hardware model for QEMU. This model needs
>>>>> a couple memory regions for MMIO.
>>>>> 
>>>>> The thing is, I don’t particularly care what the physical address of
>>>>> the memory region is (so long as it doesn’t overlap with any other
>>>>> memory region).
>>>> Curious, what's your mechanism for giving the auto allocated address
>>>> to the guest?
>>> We have one memory space that is fixed. The plan is to put the addresses of
>> the automatically allocated locations in the fixed space.
>> 
>> That sounds exactly like what I've been working on. The first incarnation was
>> called "platform bus", the second "platform devices", the current work is 
>> going
>> to be "sysbus hints" - but it's WIP.
> 
> Hmm, it sounds very similar. Out of curiosity, is there any relation to Linux 
> platform devices?

There's inspiration from them. After all, both are basically abstractions of 
the same things ;).

> 
>> 
>>> 
>>>>> 
>>>>> I was wondering if QEMU is able to ‘allocate’ a memory region for
>>>>> hardware
>>>>> (IE: I call into something saying I need a memory region X bytes long,
>>>>> and QEMU returns with a pointer to a memory region X bytes long).
>>>> Do you have full control over the memory region you are adding these sub-
>>>> regions too and can you implement a "for-everything" allocator on the
>> machine
>>>> level?
>>> We want to be able to put these sub-regions anywhere in memory-space, so a
>> "for-everything" allocator isn't really a good option.
>> 
>> Why not?
> 
> I think I misinterpreted the meaning of the term 'full control'.
> Right now, the sole purpose of the guest machine is to validate this hardware 
> model. I can change the hardware models in the guest as needed (although I 
> hope to keep them the same). In that sense, I have full control over the 
> memory region. 
> 
>> 
>>> 
>>>>> 
>>>>> Can QEMU do this? was looking at the various flavors of
>>>>> memory_region_add_subregion(), but they all seem to require a hardware
>>>>> offset…
>>>> Alex's addressless -device work may be related but it's more about command
>>>> line usability. Autoallocation of MMIO addresses is a feature there 
>>>> however.
>>> Where is this code located? I have been looking, but I haven’t been able to 
>>> find
>> it yet. Is this called by qdev_device_add()?
>> 
>> It's not upstream yet ;).
> 
> Aah, that explains why I couldn't find it :P
> 
> 
> It seems like the answer to my initial question, "can qemu add a memory 
> region for hardware without being given a specific address" is "Not yet".

Exactly. But you can also add a "it will very soon". :)

Alex

> 
> Thanks,
> Sean