Re: [Qemu-devel] [PATCH v2 6/8] pc: memhp: do not export nvdimm's memory via _CRS

[Xiao Guangrong <guangrong.xiao@linux.intel.com>]

On 10/03/2016 09:21 PM, Igor Mammedov wrote:
> On Fri, 12 Aug 2016 14:54:08 +0800
> Xiao Guangrong <guangrong.xiao@linux.intel.com> wrote:
>
>> nvdimm's memory info can not exported via _CRS, instead, it is reported
>> by NFIT/FIT
>>
>> This patch let _CRS return zero for both memory address and memory size
>> if it is a nvdimm device inserted to the slot
> I'm not sure if it's right thing to do.
> As it's relatively new, spec isn't clear about NVDIMM hotplug
> process and how it's related to PNP0C80 memory devices.
>
> The thing is that notify to PNP0C80 will trigger regular
> memory hotplug which would expect a valid _CRS and
> I won't even try to predict reaction of different guests
> on such behavior.
>
> So far exposing NFIT was sufficient for guest to work with
> NVDIMMs at startup. So I'd assume NVDIMM_ROOT._FIT() would
> provide sufficient info to hot-plug NVDIMM and allow
> NVDIMM driver to handle it.
>
> The only case of using PNP0C80 with NVDIMM, I'd imagine, is
> when one would like to expose NVDIMM as conventional RAM and
> make guest OS use it as such, which is probably not what you'd
> intended do here.
>
> Question is should/could NVDIMM hotplug work without using
> PNP0C80?

Some confusion i got when i was reading ACPI spec. I thing you
are right that notifying memory device (PNP0C80) is needed only
if the nvdimm is trying to export conventional RAM.

>
> One could reuse/share memhotplug GPE._E03 to notify NVDIMM_ROOT
> but even that is not necessary as NVDIMM has its own QEMU<->guest
> interface and could just take the next free _E04 handler.
> So I'd suggest to redo this and 7/8 patches to implement
> independent (of memhotplug) NVDIMM hotplug as a starting point.

Based on ACPI Spec, the memory device (PNP0C80) and nvdimm device
is notified by the same interruption:

Scope (\_GPE)
{
Method (_L00) {
Notify (\_SB.NVDR, 0x80) // Notify to NVDIMM root device
Notify (\_SB.MEM0, 1) // Device Check to Memory Module
}
}

So, it is better to reuse _E03 and only notify NVDIMM device if the
hotplug event is triggered on a slot with nvdimm device attached?