kconfig: add sanity checks for SPL configuration

For the SPL configuration, "make <dir>/<target>" is used.
Here,
  <dir> is either "spl" or "tpl"
  <target> is one of "config", "menuconfig", "xconfig", etc.

This commit adds two checks:

[1] If <dir> is given an unsupported subimage, the configuration
    should error out like this:

  $ make qpl/menuconfig
  ***
  *** "make qpl/menuconfig" is not supported.
  ***

[2] Make sure that "CONFIG_SPL" is enabled in the ".config" before
    running "make spl/menuconfig.  Otherwise, the SPL image
    is not built at all.  Having "spl/.config" makes no sense.
    In such a case, the configuration should exit with a message:

  $ make spl/menuconfig
  ***
  *** Create ".config" with "CONFIG_SPL" enabled
  *** before "make spl/menuconfig".
  ***
Signed-off-by: NMasahiro Yamada <yamada.m@jp.panasonic.com>
Suggested-by: NSimon Glass <sjg@chromium.org>

scripts/multiconfig.sh

@@ -252,6 +252,35 @@ do_savedefconfig () {
 	IFS=$save_IFS
 }
 
+# Some sanity checks before running "make <objdir>/<target>",
+# where <objdir> should be either "spl" or "tpl".
+# Doing "make spl/menuconfig" etc. on a non-SPL board makes no sense.
+# It should be allowed only when ".config" exists and "CONFIG_SPL" is enabled.
+#
+# Usage:
+#   check_enabled_sumbimage <objdir>/<target> <objdir>
+check_enabled_subimage () {
+
+	case $2 in
+	spl|tpl) ;;
+	*)
+		echo >&2 "***"
+		echo >&2 "*** \"make $1\" is not supported."
+		echo >&2 "***"
+		exit 1
+		;;
+	esac
+	test -r "$KCONFIG_CONFIG" && get_enabled_subimages | grep -q $2 || {
+		config=CONFIG_$(echo $2 | tr '[a-z]' '[A-Z]')
+
+		echo >&2 "***"
+		echo >&2 "*** Create \"$KCONFIG_CONFIG\" with \"$config\" enabled"
+		echo >&2 "*** before \"make $1\"."
+		echo >&2 "***"
+		exit 1
+	}
+}
+
 # Usage:
 #   do_others <objdir>/<target>
 # The field "<objdir>/" is typically empy, "spl/", "tpl/" for Normal, SPL, TPL,
@@ -265,6 +294,7 @@ do_others () {
 		objdir=
 	else
 		objdir=${1%/*}
+		check_enabled_subimage $1 $objdir
 	fi
 
 	run_make_config $target $objdir