From 9c949b0dcab5e3b82d066da0041deae2ef2e4d8c Mon Sep 17 00:00:00 2001
From: Felix Fietkau <nbd@openwrt.org>
Date: Wed, 6 Jan 2016 18:37:42 +0000
Subject: build: suppress unnecessary kernel config rewrites to speed up build

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

SVN-Revision: 48143
---
 include/kernel-defaults.mk | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/include/kernel-defaults.mk b/include/kernel-defaults.mk
index d37787a44b..f3b5e421d1 100644
--- a/include/kernel-defaults.mk
+++ b/include/kernel-defaults.mk
@@ -80,6 +80,7 @@ ifeq ($(CONFIG_TARGET_ROOTFS_INITRAMFS),y)
   endif
 
   define Kernel/SetInitramfs
+	rm -f $(LINUX_DIR)/.config.prev
 	mv $(LINUX_DIR)/.config $(LINUX_DIR)/.config.old
 	$(call Kernel/SetInitramfs/PreConfigure)
 	echo 'CONFIG_INITRAMFS_ROOT_UID=$(shell id -u)' >> $(LINUX_DIR)/.config
@@ -96,9 +97,9 @@ else
 endif
 
 define Kernel/SetNoInitramfs
-	mv $(LINUX_DIR)/.config $(LINUX_DIR)/.config.old
-	grep -v INITRAMFS $(LINUX_DIR)/.config.old > $(LINUX_DIR)/.config
-	echo 'CONFIG_INITRAMFS_SOURCE=""' >> $(LINUX_DIR)/.config
+	mv $(LINUX_DIR)/.config.set $(LINUX_DIR)/.config.old
+	grep -v INITRAMFS $(LINUX_DIR)/.config.old > $(LINUX_DIR)/.config.set
+	echo 'CONFIG_INITRAMFS_SOURCE=""' >> $(LINUX_DIR)/.config.set
 endef
 
 define Kernel/Configure/Default
@@ -109,11 +110,15 @@ define Kernel/Configure/Default
 	echo "# CONFIG_KALLSYMS_ALL is not set" >> $(LINUX_DIR)/.config.target
 	echo "# CONFIG_KALLSYMS_UNCOMPRESSED is not set" >> $(LINUX_DIR)/.config.target
 	$(SCRIPT_DIR)/metadata.pl kconfig $(TMP_DIR)/.packageinfo $(TOPDIR)/.config $(KERNEL_PATCHVER) > $(LINUX_DIR)/.config.override
-	$(SCRIPT_DIR)/kconfig.pl 'm+' '+' $(LINUX_DIR)/.config.target /dev/null $(LINUX_DIR)/.config.override > $(LINUX_DIR)/.config
+	$(SCRIPT_DIR)/kconfig.pl 'm+' '+' $(LINUX_DIR)/.config.target /dev/null $(LINUX_DIR)/.config.override > $(LINUX_DIR)/.config.set
 	$(call Kernel/SetNoInitramfs)
 	rm -rf $(KERNEL_BUILD_DIR)/modules
+	cmp -s $(LINUX_DIR)/.config.set $(LINUX_DIR)/.config.prev || { \
+		cp $(LINUX_DIR)/.config.set $(LINUX_DIR)/.config; \
+		cp $(LINUX_DIR)/.config.set $(LINUX_DIR)/.config.prev; \
+	}
 	$(_SINGLE) [ -d $(LINUX_DIR)/user_headers ] || $(MAKE) $(KERNEL_MAKEOPTS) INSTALL_HDR_PATH=$(LINUX_DIR)/user_headers headers_install
-	$(SH_FUNC) grep '=[ym]' $(LINUX_DIR)/.config | LC_ALL=C sort | md5s > $(LINUX_DIR)/.vermagic
+	$(SH_FUNC) grep '=[ym]' $(LINUX_DIR)/.config.set | LC_ALL=C sort | md5s > $(LINUX_DIR)/.vermagic
 endef
 
 define Kernel/Configure/Initramfs
-- 
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