cbmem: Add comment for cbmem_top returning NULL if backing store is not ready

Board or chipset needs to ensure that cbmem backing store is ready
when returning the cbmem top address. cbmem infrastructure has no
support for checking the validity of the backing store/address.

E.g.: If romstage handles cbmem coming online, chipset or board need
to ensure that call to cbmem_top in romstage returns NULL if the
backing store is not yet initialized.

Add a comment to ensure that developers know this requirement while
implementing cbmem_top for future chipsets/boards.

Change-Id: I0086b8e528f65190b764a84365cf9bf970b69c3f
Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: https://review.coreboot.org/14181
Tested-by: build bot (Jenkins)
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

0 files changed, 0 insertions, 0 deletions