kernel: Improve kernel config rules

This makes sure that all the kernel config fragments used for the merge
are emitted to the kernel build directory to help in any needed debugging.
Additionally drops redundant warnings about missing prerequisites, and
makes the output directory an order-only dependency.

Change-Id: If3b56b3a8c1a16b57026d64696b7a0ccf6261a75

1 files changed, 31 insertions, 26 deletions

diff --git a/kernel.mk b/kernel.mk
index 9fdd75c..294def8 100644
--- a/kernel.mk
+++ b/kernel.mk
@@ -45,6 +45,11 @@ ifeq ($(TARGET_KERNEL_ARCH),)
 $(error TARGET_KERNEL_ARCH not defined)
 endif
 
+# This is optional, but we'd like to use it as a dependency.
+ifndef TARGET_KERNEL_CONFIGS
+TARGET_KERNEL_CONFIGS := /dev/null
+endif
+
 # Check target arch.
 KERNEL_TOOLCHAIN_ABS := $(realpath $(TARGET_TOOLCHAIN_ROOT)/bin)
 TARGET_KERNEL_ARCH := $(strip $(TARGET_KERNEL_ARCH))
@@ -107,8 +112,12 @@ endif
 # Set the output for the kernel build products.
 KERNEL_OUT := $(TARGET_OUT_INTERMEDIATES)/KERNEL_OBJ
 
-KERNEL_CONFIG := $(KERNEL_OUT)/.config
+# The kernel configs, in precedence order.
+KERNEL_CONFIG_DEFAULT := $(KERNEL_OUT)/.config.default
+KERNEL_CONFIG_RECOMMENDED := $(KERNEL_OUT)/.config.recommended
+KERNEL_CONFIG_PRODUCT := $(KERNEL_OUT)/.config.product
 KERNEL_CONFIG_REQUIRED := $(KERNEL_OUT)/.config.required
+KERNEL_CONFIG := $(KERNEL_OUT)/.config
 
 KERNEL_BIN := $(KERNEL_OUT)/arch/$(KERNEL_SRC_ARCH)/boot/$(KERNEL_NAME)
 
@@ -128,35 +137,31 @@ KERNEL_HEADERS_INSTALL := $(KERNEL_OUT)/usr
 $(KERNEL_OUT):
 	mkdir -p $(KERNEL_OUT)
 
+$(KERNEL_CONFIG_DEFAULT): $(TARGET_KERNEL_SRC)/arch/$(KERNEL_SRC_ARCH)/configs/$(TARGET_KERNEL_DEFCONFIG) | $(KERNEL_OUT)
+	$(hide) cat $< > $@
+
+$(KERNEL_CONFIG_RECOMMENDED): $(KERNEL_CONFIGS_RECOMMENDED) | $(KERNEL_OUT)
+	$(hide) cat $< > $@
+
+$(KERNEL_CONFIG_PRODUCT): $(TARGET_KERNEL_CONFIGS) | $(KERNEL_OUT)
+	$(hide) cat $< > $@
+
 # Merge the required kernel config elements.
-$(KERNEL_CONFIG_REQUIRED): $(KERNEL_OUT) \
-			   $(KERNEL_CONFIGS_COMMON) $(KERNEL_CONFIGS_ARCH) \
-			   $(KERNEL_CONFIGS_VER) $(KERNEL_CONFIGS_VER_ARCH)
-	$(hide) if [ ! -f $(KERNEL_CONFIGS_ARCH) ] ; then \
-		echo "Missing common kernel configs for $(KERNEL_ARCH)"; \
-		echo "$(KERNEL_CONFIGS_ARCH)"; \
-		exit 1; \
-	fi
-	$(hide) if [ ! -f $(KERNEL_CONFIGS_VER) ] ; then \
-		echo "Missing common $(KERNEL_VERSION) kernel configs"; \
-		echo "$(KERNEL_CONFIGS_VER)"; \
-		exit 1; \
-	fi
-	$(hide) if [ ! -f $(KERNEL_CONFIGS_VER_ARCH) ] ; then \
-		echo "Missing $(KERNEL_VERSION) kernel configs for $(KERNEL_ARCH)"; \
-		echo "$(KERNEL_CONFIGS_VER_ARCH)"; \
-		exit 1; \
-	fi
-	$(hide) cat $(KERNEL_CONFIGS_COMMON) $(KERNEL_CONFIGS_ARCH) \
-		    $(KERNEL_CONFIGS_VER) $(KERNEL_CONFIGS_VER_ARCH) > $@
+$(KERNEL_CONFIG_REQUIRED): $(KERNEL_CONFIGS_COMMON) $(KERNEL_CONFIGS_ARCH) \
+			   $(KERNEL_CONFIGS_VER) $(KERNEL_CONFIGS_VER_ARCH) \
+			   | $(KERNEL_OUT)
+	$(hide) cat $(filter-out $(KERNEL_OUT),$^) > $@
 
 # Merge the final target kernel config.
-$(KERNEL_CONFIG): $(KERNEL_OUT) $(KERNEL_CONFIG_REQUIRED)
+$(KERNEL_CONFIG): $(KERNEL_CONFIG_DEFAULT) $(KERNEL_CONFIG_RECOMMENDED) \
+		  $(KERNEL_CONFIG_PRODUCT) $(KERNEL_CONFIG_REQUIRED) \
+		  | $(KERNEL_OUT)
+	$(hide) echo Merging kernel config
 	$(KERNEL_MERGE_CONFIG) $(TARGET_KERNEL_SRC) $(realpath $(KERNEL_OUT)) \
 		$(KERNEL_ARCH) $(KERNEL_CROSS_COMPILE) \
-		arch/$(KERNEL_SRC_ARCH)/configs/$(TARGET_KERNEL_DEFCONFIG) \
-		$(realpath $(KERNEL_CONFIGS_RECOMMENDED)) \
-		$(TARGET_KERNEL_CONFIGS) \
+		$(realpath $(KERNEL_CONFIG_DEFAULT)) \
+		$(realpath $(KERNEL_CONFIG_RECOMMENDED)) \
+		$(realpath $(KERNEL_CONFIG_PRODUCT)) \
 		$(realpath $(KERNEL_CONFIG_REQUIRED))
 
 # Disable CCACHE_DIRECT so that header location changes are noticed.
@@ -171,7 +176,7 @@ define build_kernel
 		$(1)
 endef
 
-$(KERNEL_BIN): $(KERNEL_OUT) $(KERNEL_CONFIG)
+$(KERNEL_BIN): $(KERNEL_CONFIG) | $(KERNEL_OUT)
 	$(hide) echo "Building $(KERNEL_ARCH) $(KERNEL_VERSION) kernel ..."
 	$(hide) rm -rf $(KERNEL_OUT)/arch/$(KERNEL_ARCH)/boot/dts
 	$(hide) rm -rf $(PRODUCT_OUT)/kernel.dtb $(PRODUCT_OUT)/kernel-and-dtb