cmake: Fall back to ZEPHYR_BASE when the board is not in BOARD_ROOT

It is very inconvenient to maintain an application that both runs on a
Zephyr board and an out-of-tree board.

It forces one to write build scripts like this in the app:

if(BOARD STREQUAL my_out_of_tree_board)
  set(BOARD_ROOT some/out/of/tree/board/path)
endif()

To avoid this we change the semantics of BOARD_ROOT. Instead of it
being a path to the board root it is now a prioritized list of board
root directories. Zephyr will append ZEPHYR_BASE to BOARD_ROOT.

This ensures that Zephyr boards can be used when the out-of-tree board
directory can not supply the requested board.

Signed-off-by: Sebastian Bøe <sebastian.boe@nordicsemi.no>

boards/CMakeLists.txt

@@ -2,7 +2,7 @@
 # error if it is missing
 
 if(EXISTS ${BOARD_DIR}/CMakeLists.txt)
-  if(BOARD_ROOT)
+  if(USING_OUT_OF_TREE_BOARD)
 	set(build_dir boards/${ARCH}/${BOARD})
   else()
 	unset(build_dir)

cmake/app/boilerplate.cmake

@@ -189,12 +189,9 @@ message(STATUS "Selected BOARD ${BOARD}")
 # Store the selected board in the cache
 set(CACHED_BOARD ${BOARD} CACHE STRING "Selected board")
 
-# Use BOARD to search zephyr/boards/** for a _defconfig file,
-# e.g. zephyr/boards/arm/96b_carbon_nrf51/96b_carbon_nrf51_defconfig. When
-# found, use that path to infer the ARCH we are building for.
-if(NOT BOARD_ROOT)
-  set(BOARD_ROOT ${ZEPHYR_BASE})
-endif()
+# 'BOARD_ROOT' is a prioritized list of directories where boards may
+# be found. It always includes ${ZEPHYR_BASE} at the lowest priority.
+list(APPEND BOARD_ROOT ${ZEPHYR_BASE})
 
 if(NOT SOC_ROOT)
   set(SOC_DIR ${ZEPHYR_BASE}/soc)
@@ -202,7 +199,21 @@ else()
   set(SOC_DIR ${SOC_ROOT}/soc)
 endif()
 
-find_path(BOARD_DIR NAMES "${BOARD}_defconfig" PATHS ${BOARD_ROOT}/boards/*/* NO_DEFAULT_PATH)
+# Use BOARD to search for a '_defconfig' file.
+# e.g. zephyr/boards/arm/96b_carbon_nrf51/96b_carbon_nrf51_defconfig.
+# When found, use that path to infer the ARCH we are building for.
+foreach(root ${BOARD_ROOT})
+  # NB: find_path will return immediately if the output variable is
+  # already set
+  find_path(BOARD_DIR
+	NAMES ${BOARD}_defconfig
+	PATHS ${root}/boards/*/*
+	NO_DEFAULT_PATH
+	)
+  if(BOARD_DIR AND NOT (${root} STREQUAL ${ZEPHYR_BASE}))
+	set(USING_OUT_OF_TREE_BOARD 1)
+  endif()
+endforeach()
 
 assert_with_usage(BOARD_DIR "No board named '${BOARD}' found")
 

cmake/extensions.cmake

@@ -1091,10 +1091,11 @@ macro(assert_with_usage test comment)
   if(NOT ${test})
     message(${comment})
     message("see usage:")
+	string(REPLACE ";" " " BOARD_ROOT_SPACE_SEPARATED "${BOARD_ROOT}")
     execute_process(
       COMMAND
       ${CMAKE_COMMAND}
-      -DBOARD_ROOT=${BOARD_ROOT}
+      -DBOARD_ROOT_SPACE_SEPARATED=${BOARD_ROOT_SPACE_SEPARATED}
       -P ${ZEPHYR_BASE}/cmake/usage/usage.cmake
       )
     message(FATAL_ERROR "Invalid usage")

cmake/usage/CMakeLists.txt

@@ -1,7 +1,9 @@
+string(REPLACE ";" " " BOARD_ROOT_SPACE_SEPARATED "${BOARD_ROOT}")
+
 add_custom_target(
   usage
   ${CMAKE_COMMAND}
-  -DBOARD_ROOT=${BOARD_ROOT}
+  -DBOARD_ROOT_SPACE_SEPARATED=${BOARD_ROOT_SPACE_SEPARATED}
   -P ${CMAKE_CURRENT_SOURCE_DIR}/usage.cmake
   )
 

cmake/usage/usage.cmake

@@ -12,27 +12,29 @@ set(arch_list
   xtensa
   )
 
-set(board_dir ${BOARD_ROOT}/boards)
+string(REPLACE " " ";" BOARD_ROOT "${BOARD_ROOT_SPACE_SEPARATED}")
 
 foreach(arch ${arch_list})
-  set(board_arch_dir ${board_dir}/${arch})
+  foreach(root ${BOARD_ROOT})
+	set(board_arch_dir ${root}/boards/${arch})
 
-  # Match the .yanl files in the board directories to make sure we are
-  # finding boards, e.g. qemu_xtensa/qemu_xtensa.yaml
-  file(GLOB_RECURSE yamls_for_${arch}
-    RELATIVE ${board_arch_dir}
-    ${board_arch_dir}/*.yaml
-    )
+	# Match the .yanl files in the board directories to make sure we are
+	# finding boards, e.g. qemu_xtensa/qemu_xtensa.yaml
+	file(GLOB_RECURSE yamls_for_${arch}
+      RELATIVE ${board_arch_dir}
+      ${board_arch_dir}/*.yaml
+      )
 
-  # The above gives a list like
-  # nrf51_blenano/nrf51_blenano_yaml;nrf51_pca10028/nrf51_pca10028_yaml
-  # we construct a list of board names by removing both the .yaml
-  # suffix and the path.
-  set(boards_for_${arch} "")
-  foreach(yaml_path ${yamls_for_${arch}})
-    get_filename_component(board ${yaml_path} NAME_WE)
+	# The above gives a list like
+	# nrf51_blenano/nrf51_blenano_yaml;nrf51_pca10028/nrf51_pca10028_yaml
+	# we construct a list of board names by removing both the .yaml
+	# suffix and the path.
+	set(boards_for_${arch} "")
+	foreach(yaml_path ${yamls_for_${arch}})
+      get_filename_component(board ${yaml_path} NAME_WE)
 
-    list(APPEND boards_for_${arch} ${board})
+      list(APPEND boards_for_${arch} ${board})
+	endforeach()
   endforeach()
 endforeach()
 

samples/application_development/out_of_tree_board/sample.yaml

@@ -4,7 +4,7 @@ sample:
 tests:
   boards.out_of_tree:
     tags: out_of_tree
-    platform_whitelist: nrf52840_pca10056
+    platform_whitelist: nrf52840_pca10056 nrf52_pca10040
     harness: console
     harness_config:
       type: one_line