The base-hw kernel on x86_64 currently assumes 254 MiB of RAM. The RAM
region is subtracted from the I/O mem allocator and therefore this range
is not available for device I/O.
If qemu is started with -m 128, the region for (emulated) PCI config
space access lies within this region and I/O mem allocation in the
pci_drv will fail. Giving qemu more RAM moves the PCI config space out
of the 254 MiB region, making the run/libc_ffat scenario with acpi work.
Alexy Gallardo Segura
Reto Buerki
Josef Söntgen