Make usage of top-level make easier, drop 'all' target (#4040)

* Make usage of top-level make easier, drop 'all' target

Make it easier when using top-level make - proxy all possible commands to
Buildroot make and only wrap build for individual target builds. This way it's
still possible to run e.g. 'make ova' which would read the defconfig and run
the build, while we can also use the top-level make in the same way as it's in
vanilla Buildroot.

Target 'all' was dropped in favor of Buildroot 'make' without any arguments -
as it's fairly pointless to run all builds sequentially. With the current 19
targets it would take about a day even on a decent hardware and the build
artifacts would be lost in the process.

* Show warning only if BR2_DEFCONFIG changes

* Wait for 10s or input if defconfig differs

Makefile

@@ -14,37 +14,46 @@ else
 override O := $(BUILDDIR)/$(O)
 endif
 
-.NOTPARALLEL: $(TARGETS) $(TARGETS_CONFIG) all
+################################################################################
 
-.PHONY: $(TARGETS) $(TARGETS_CONFIG) all buildroot-help help
+COLOR_STEP := $(shell tput smso 2>/dev/null)
+COLOR_WARN := $(shell (tput setab 3; tput setaf 0) 2>/dev/null)
+TERM_RESET := $(shell tput sgr0 2>/dev/null)
 
-all: $(TARGETS)
+################################################################################
+
+.NOTPARALLEL: $(TARGETS) $(TARGETS_CONFIG) default
+
+.PHONY: $(TARGETS) $(TARGETS_CONFIG) default buildroot-help help
+
+# fallback target when target undefined here is given
+.DEFAULT:
+	@echo "$(COLOR_STEP)=== Falling back to Buildroot target '$@' ===$(TERM_RESET)"
+	$(MAKE) -C $(BUILDROOT) O=$(O) BR2_EXTERNAL=$(BUILDROOT_EXTERNAL) "$@"
+
+# default target when no target is given - must be first in Makefile
+default:
+	$(MAKE) -C $(BUILDROOT) O=$(O) BR2_EXTERNAL=$(BUILDROOT_EXTERNAL)
 
 $(TARGETS_CONFIG): %-config:
-	@echo "config $*"
+	@if [ -f $(O)/.config ] && ! grep -q 'BR2_DEFCONFIG="$(DEFCONFIG_DIR)/$*_defconfig"' $(O)/.config; then \
+		echo "$(COLOR_WARN)WARNING: Output directory '$(O)' already contains files for another target!$(TERM_RESET)"; \
+		echo "         Before running build for a different target, run 'make distclean' first."; \
+		echo ""; \
+		bash -c 'read -t 10 -p "Waiting 10s, press enter to continue or Ctrl-C to abort..."' || true; \
+	fi
+	@echo "$(COLOR_STEP)=== Using $*_defconfig ===$(TERM_RESET)"
 	$(MAKE) -C $(BUILDROOT) O=$(O) BR2_EXTERNAL=$(BUILDROOT_EXTERNAL) "$*_defconfig"
 
 $(TARGETS): %: %-config
-	@echo "build $@"
+	@echo "$(COLOR_STEP)=== Building $@ ===$(TERM_RESET)"
 	$(MAKE) -C $(BUILDROOT) O=$(O) BR2_EXTERNAL=$(BUILDROOT_EXTERNAL)
 
-	# Do not clean when building for one target
-ifneq ($(words $(filter $(TARGETS),$(MAKECMDGOALS))), 1)
-	@echo "clean $@"
-	$(MAKE) -C $(BUILDROOT) O=$(O) BR2_EXTERNAL=$(BUILDROOT_EXTERNAL) clean
-endif
-	@echo "finished $@"
-
-.DEFAULT:
-	@echo "falling back to Buildroot target '$@'"
-	$(MAKE) -C $(BUILDROOT) O=$(O) BR2_EXTERNAL=$(BUILDROOT_EXTERNAL) "$@"
-
 buildroot-help:
 	$(MAKE) -C $(BUILDROOT) O=$(O) BR2_EXTERNAL=$(BUILDROOT_EXTERNAL) help
 
 help:
 	@echo "Run 'make <target>' to build a target image."
-	@echo "Run 'make all' to build all target images."
 	@echo "Run 'make <target>-config' to configure buildroot for a target."
 	@echo ""
 	@echo "Supported targets: $(TARGETS)"