Hi,
In fact I was thinking that we can add custom "OEMx" tables to ACPI and dump them using acpi tools. I mean we can add the hooks to ACPI so cbmem stuff is available per table in ACPI.
The AMD chipsets needs to use NVRAM because there is stored DQS driving values for memory controller. Also the cbmem address is stored there because one cannot find it very easily if there is frambuffer (and on AMD all access is uncached that time). This NVRAM is not CMOS it is just 256 bytes of storage which survives S3 state.
Thanks, Rudolf