[Buildroot] [PATCH 1/1] linux: avoid multiple dtb append on uImages

[derosier at gmail.com <derosier@gmail.com>]

From: Steve deRosier <steve.derosier@lairdtech.com>

If using appended dtbs on uImages, a 'make linux-rebuild' will end up just
adding the new dtb after the previous dtb if all you did was modify the
device tree without a modification that would regenerate the zImage. This
results in a surprising effect when you boot your device: your DT changes
don't take effect because linux just loads the first dtb.

This patch fixes this little edge case by using an intermediate file for the
append work if using BR2_LINUX_KERNEL_APPEND_UIMAGE. Otherwise it must
retain the zImage naming, so the situation is unchanged for the case where
this flag is not set.

Signed-off-by: Steve deRosier <steve.derosier@lairdtech.com>
---
 linux/linux.mk |   17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/linux/linux.mk b/linux/linux.mk
index 48f9c74..d4252e3 100644
--- a/linux/linux.mk
+++ b/linux/linux.mk
@@ -245,14 +245,23 @@ endif
 endif
 
 ifeq ($(BR2_LINUX_KERNEL_APPENDED_DTB),y)
-# dtbs moved from arch/$ARCH/boot to arch/$ARCH/boot/dts since 3.8-rc1
+# If we append and create the uImage, we want to be sure not to multiple-append on
+# rebuilds, so use a temporary intermediate "zImage-dtb" and then append, but if we
+# don't use the APPENDED_UIMAGE option, we need to be sure it stays named as zImage.
+IMAGE_PLUS_DTB = zImage
+ifeq ($(BR2_LINUX_KERNEL_APPENDED_UIMAGE),y)
+	IMAGE_PLUS_DTB = zImage-dtb
 define LINUX_APPEND_DTB
+	cp $(KERNEL_ARCH_PATH)/boot/zImage $(KERNEL_ARCH_PATH)/boot/$(IMAGE_PLUS_DTB);
+endef
+endif
+# dtbs moved from arch/$ARCH/boot to arch/$ARCH/boot/dts since 3.8-rc1
+LINUX_APPEND_DTB += \
 	if [ -e $(KERNEL_ARCH_PATH)/boot/$(KERNEL_DTS_NAME).dtb ]; then \
 		cat $(KERNEL_ARCH_PATH)/boot/$(KERNEL_DTS_NAME).dtb; \
 	else \
 		cat $(KERNEL_ARCH_PATH)/boot/dts/$(KERNEL_DTS_NAME).dtb; \
-	fi >> $(KERNEL_ARCH_PATH)/boot/zImage
-endef
+	fi >> $(KERNEL_ARCH_PATH)/boot/$(IMAGE_PLUS_DTB)
 ifeq ($(BR2_LINUX_KERNEL_APPENDED_UIMAGE),y)
 # We need to generate a new u-boot image that takes into
 # account the extra-size added by the device tree at the end
@@ -263,7 +272,7 @@ LINUX_APPEND_DTB += $(sep) MKIMAGE_ARGS=`$(MKIMAGE) -l $(LINUX_IMAGE_PATH) |\
 	sed -n -e 's/Image Name:[ ]*\(.*\)/-n \1/p' -e 's/Load Address:/-a/p' -e 's/Entry Point:/-e/p'`; \
 	$(MKIMAGE) -A $(MKIMAGE_ARCH) -O linux \
 	-T kernel -C none $${MKIMAGE_ARGS} \
-	-d $(KERNEL_ARCH_PATH)/boot/zImage $(LINUX_IMAGE_PATH);
+	-d $(KERNEL_ARCH_PATH)/boot/$(IMAGE_PLUS_DTB) $(LINUX_IMAGE_PATH);
 endif
 endif
 
-- 
1.7.9.5