Re: [Qemu-devel] [Linaro-acpi] [RFC PATCH 0/7] hw/arm/virt: Dynamic ACPI v5.1 table generation

[Hanjun Guo]

On 2014-11-6 23:57, Paolo Bonzini wrote:
> On 06/11/2014 07:53, Hanjun Guo wrote:
>>> So the important question is _why_ the guest needs to see an ACPI
>>> environment. What exactly can ACPI provide to the guest that DT does not
>>> already provide, and why is that necessary? What infrastrucutre is
>>> needed for that use case?
>>
>> There is important feature called system device dynamic reconfiguration,
>> you know, hot-add/remove, if a gust need more/less memory or CPU, can we
>> add or remove them dynamically with DT? ACPI can do this, but I have no
>> idea if DT can. (Sorry, I don't know much about DT)
> 
> Indeed hot-add/remove is the single biggest AML user in x86 QEMU.
> Whether you really need it, it depends on what you are adding/removing.
> 
> For PCI there is no problem.  We can use PCIe from the beginning, and
> use PCIe hotplug support that is already in QEMU.
> 
> Memory and CPU are more problematic.  For memory we could perhaps use a
> PCI memory device, though I'm not sure if that would require drivers in
> the OS or everything just works.

I didn't see some code for hot-adding system memory as PCI device, but people
from Fujitsu is working on that in another solution - QEmu memory hot unplug
support:

https://www.mail-archive.com/address@hidden/msg251355.html

for the guest, ACPI based memory hot-add/remove was already supported.

Thanks
Hanjun