Re: [Qemu-devel] [RFC v1] Add declarations for hierarchical memory region API

[Anthony Liguori <anthony@codemonkey.ws>]

On 05/22/2011 01:39 AM, Avi Kivity wrote:
> On 05/20/2011 05:46 PM, Anthony Liguori wrote:
>> On 05/20/2011 09:40 AM, Richard Henderson wrote:
>>> On 05/20/2011 07:31 AM, Anthony Liguori wrote:
>>>> But is this a characteristic of devices or is this a characteristic
>>>> of the chipset/CPU?
>>>
>>> Chipset.
>>
>> So if the chipset only allows accesses that are 64-bit, then you'll
>> want to have hierarchical dispatch filter non 64-bit accesses and
>> raise an MCE appropriately.
>>
>> So you don't need anything in MemoryRegion, you need code in the
>> dispatch path.
>
> MemoryRegion *is* the dispatch path. Only done declaratively so we can
> flatten it whenever it changes.

We don't want dispatch to be 100% declarative.  That's what will cause 
the API to get horrendously ugly.

An example is PCI-bus level endianness conversion.  I also believe the 
Sparc IOMMU has an xor engine.

You could add a 'bool swap_endian' and an 'uint32_t xor_mask' in 
MemoryRegion but now you're adding a ton of platform specific knowledge 
to what should be an independent layer.

Regards,

Anthony Liguori

>