|Enabling CONFIG_CSM allows SeaBIOS to be built as a Compatibility Support
|Module for use with the OMVF/EDK-II UEFI firmware.
|It will provide "legacy" BIOS services for booting non-EFI operating
|systems and will also allow OVMF to display on otherwise unsupported
|video hardware by using the traditional VGA BIOS.
|Windows 2008r2 is known to use INT 10h BIOS calls even when booted via
|EFI, and the presence of a CSM makes this work as expected too.
|Having built SeaBIOS with CONFIG_CSM, you should be able to drop the
|result into your OVMF build tree at OvmfPkg/Csm/Csm16/Csm16.bin and
|then build OVMF with 'build -D CSM_ENABLE'. The SeaBIOS binary will be
|included as a discrete file within the 'Flash Volume' which is
|created, and there are tools which will extract it and allow it to be
|replaced; satisfying the requirements of the LGPL licence.
|A patch to OVMF is required, to prevent it from marking the region from
|0xC0000-0xFFFFF as read-only before invoking our Legacy16Boot method. See