[Qemu-arm] Expand ECAM region in machvirt 2_13?

[Auger Eric]

Hi,

I would like to resume the discussion on extending the number of PCI
buses to 256 (as in Q35) as a follow-up of past discussions:
https://lists.gnu.org/archive/html/qemu-devel/2018-01/msg03631.html.

With the current 16MB ECAM region we are limited to 16 PCIe busses.

Could we envision to have a 256MB ECAM region and move it to another
location beyond 256GB, in virt2_13 machine type?

Current ECAM range within [0x3f000000, 0x40000000]
would be kept unchanged for legacy and when vms->highmem is set to false.
Migration from <2_13 to >=2_13 would be allowed whereas migration from
> =2.13 to <2.13 wouldn't.

Thanks

Eric