cr50: introduce RO image skeleton

The CR50 board will have to have a very different RO image, let's make
it possible to override the default list of objects compiled by the
top level makefile with a board/chip specific list compiled in the
appropriate build.mk file.

The CR50 RO will never run on its own for long time, it will always
load an RW and go straight to it, so there is no need in running under
the OS control, using sophisticated console channel controls, etc.

The gist of the functionality is verifying the RW image to run and
setting up the hardware to allow the picked image to execute, it will
be added in the following patches. This change just provides the
plumbing and shows the 'hello world' implementation for the customized
RO image.

A better solution could be the ability to create distinct sets of make
variables for RO and RW, a tracker item was created to look into this.

BRANCH=None
BUG=chrome-os-partner:43025, chromium:551151
TEST=built and started ec.RO.hex on cr50, observed the 'hello world'
     message on the console.

Change-Id: Ie67ff28bec3a9788898e99483eedb0ef77de38cd
Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/310410
Reviewed-by: Randall Spangler <rspangler@chromium.org>
Reviewed-by: Bill Richardson <wfrichar@chromium.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/Makefile b/Makefile
index 1736fd1a85..bac644327f 100644
--- a/Makefile
+++ b/Makefile
@@ -154,7 +154,12 @@ dirs+= private private-cr51
 dirs+=$(shell find driver -type d)
 common_dirs=util
 
+ifeq ($(custom-ro_objs-y),)
 ro-objs := $(sort $(foreach obj, $(all-obj-y), $(out)/RO/$(obj)))
+else
+ro-objs := $(sort $(foreach obj, $(custom-ro_objs-y), $(out)/RO/$(obj)))
+endif
+
 rw-objs := $(sort $(foreach obj, $(all-obj-y), $(out)/RW/$(obj)))
 
 # Don't include the shared objects in the RO/RW image if we're enabling