Re: [RFC v4 3/3] hw/cxl: Multi-Region CXL Type-3 Devices (Volatile and Persistent)

[Gregory Price]

> I think an address space needs a memory region, not a memdev.
> Initialize a container region with memory_region_init()
> We could then add the two memdev associated regions (with different 
> attributes) as subregions using memory_region_add_subregion()
> 
> Similar is done for the system memory
> https://elixir.bootlin.com/qemu/latest/source/softmmu/physmem.c#L2675
> creates it.  Then it's mostly accessed by get_system_memory()
> 
> Memory is then added to that at particular base addresses via for example
> https://elixir.bootlin.com/qemu/latest/source/hw/arm/virt.c#L2210
> and similar.
> I think we can do the same here.
>

Ah, I'm just confused then, this seems reasonable

> Curious question on this lot. How are you testing it?  Some exciting scripts
> to bring the hdm decoders up etc for the volatile region? Or some prototype
> driver code?

Unfortunately I got pulled off this work for a bit to handle something
more pressing.  I have only tested that the existing functionality
(persistent mode) works as intended, and that at least the ndctl/cxl
tools report capacity as expected.

As of right now there is no code in the driver to actually touch these
regions in a way that works to be able to online these volatile regions
- at least so far as I know.

I don't remember where I left off, but some pmem-to-ram tutorials online
suggest you could online pmem regions like this

cxl create-region -d decoder0.0 -m mem0
echo offline > /sys/devices/system/memory/auto_online_blocks
ndctl create-namespace -f --mode devdax --continue
daxctl enable-device [device name]
daxctl reconfigure-device --mode=system-ram all

However I don't think this is successful in creating the dax devices,
and therefore the reconfiguring into ram.