cmake: extensions: board revisions can be optional

Add a new option to `board_check_revision` that can make specifying a
board revision optional. This makes it easier to work with boards that
can come in a base variant with extensions. For example Fanstel BLE
modules that come with/without power amplifiers.

Signed-off-by: Jordan Yates <[email protected]>

Author: Jordan Yates

cmake/modules/extensions.cmake

@@ -863,6 +863,11 @@ endfunction()
 #                             command line, which means:
 #                             1.0.0 == 1.0 == 1
 #
+# OPTIONAL: Revision specifier is optional. If revision is not provided the base
+#           board will be used. If both `EXACT` and `OPTIONAL` are given, then
+#           specifying the revision is optional, but if it is given then the
+#           `EXACT` requirements apply. Mutually exclusive with `DEFAULT_REVISION`.
+#
 # EXACT: Revision is required to be an exact match. As example, available revisions are:
 #        0.1.0 and 0.3.0, and user provides 0.2.0, then an error is reported
 #        when `EXACT` is given.
@@ -890,15 +895,21 @@ endfunction()
 #                   will be used as a valid revision for the board.
 #
 function(board_check_revision)
-  set(options EXACT)
+  set(options OPTIONAL EXACT)
   set(single_args FORMAT DEFAULT_REVISION HIGHEST_REVISION)
   set(multi_args  VALID_REVISIONS)
   cmake_parse_arguments(BOARD_REV "${options}" "${single_args}" "${multi_args}" ${ARGN})
 
   string(TOUPPER ${BOARD_REV_FORMAT} BOARD_REV_FORMAT)
 
+  if(DEFINED BOARD_REV_DEFAULT_REVISION AND BOARD_REV_OPTIONAL)
+    message(FATAL_ERROR "Arguments BOARD_REVISION and OPTIONAL are mutually exclusive")
+  endif()
+
   if(NOT DEFINED BOARD_REVISION)
-    if(DEFINED BOARD_REV_DEFAULT_REVISION)
+    if(BOARD_REV_OPTIONAL)
+      return()
+    elseif(DEFINED BOARD_REV_DEFAULT_REVISION)
       set(BOARD_REVISION ${BOARD_REV_DEFAULT_REVISION})
       set(BOARD_REVISION ${BOARD_REVISION} PARENT_SCOPE)
     else()

doc/hardware/porting/board_porting.rst

@@ -695,7 +695,7 @@ board_check_revision() details
 .. code-block:: cmake
 
    board_check_revision(FORMAT <LETTER | NUMBER | MAJOR.MINOR.PATCH>
-                        [EXACT]
+                        [OPTIONAL EXACT]
                         [DEFAULT_REVISION <revision>]
                         [HIGHEST_REVISION <revision>]
                         [VALID_REVISIONS <revision> [<revision> ...]]
@@ -712,6 +712,12 @@ This function supports the following arguments:
   ambiguity, so only :file:`<board>_1_0_0.conf` and
   :file:`<board>_1_0_0.overlay` are allowed.
 
+* ``OPTIONAL``: if given, a revision is not required to be specified.
+  If the revision is not supplied, the base board is used with no overlays.
+  Can be combined with ``EXACT``, in which case providing the revision is
+  optional, but if given the ``EXACT`` rules apply. Mutually exclusive with
+  ``DEFAULT_REVISION``.
+
 * ``EXACT``: if given, the revision is required to be an exact match.
   Otherwise, the closest matching revision not greater than the user's choice
   will be selected.