On Tue, 2019-01-22 at 16:13 +0000, Ni, Ray wrote:
> David,
> I'd like to re-start the discussion.
> Could you please kindly explain the background/reason of adding CSM
> support in OVMF?
> Maybe knowing the reason can help to make further decisions of
> whether to
> A. keep it outside OvmfPkg
> B. keep it inside OvmfPkg
> C. maybe have a chance to just remove the CSM support after
> revisiting


The idea was to make it simple to have a single firmware image for
virtual machines which would support both UEFI and Legacy boot for
guests simultaneously.

In libvirt there has been an alternative approach, where the BIOS image
is switched between OVMF and SeaBIOS according to the configuration of
the guest VM.

That's fine for libvirt, but in situations where VM hosting is provided
as a service, it becomes quite painful to manage the 'UEFI' vs.
'Legacy' flags on guest images and then switch firmware images
accordingly. A one-size-fits-all BIOS using OVMF+CSM is very much
preferable.