Makefile: add target to produce a SPL compatible uImage

This is mostly useful during the initial port of barebox to a new
board which is supported by u-boot. It also allows starting barebox
from a SRAM-based u-boot SPL.

A different load address can be set like this:
make barebox.uimage UIMAGE_BASE=0x80000000

Also add barebox.ubl to CLEAN_FILES.

Signed-off-by: Jan Luebbe <jlu@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

.gitignore

@@ -35,6 +35,7 @@ barebox.srec
 barebox.netx
 barebox.s5p
 barebox.ubl
+barebox.uimage
 barebox.map
 System.map
 Module.symvers

Makefile

@@ -680,6 +680,22 @@ ifndef CONFIG_PBL_IMAGE
 	$(call cmd,check_file_size,$(CONFIG_BAREBOX_MAX_IMAGE_SIZE))
 endif
 
+# By default the uImage load address is 2MB below CONFIG_TEXT_BASE,
+# leaving space for the compressed PBL image at 1MB below CONFIG_TEXT_BASE.
+UIMAGE_BASE ?= $(shell printf "0x%08x" $$(($(CONFIG_TEXT_BASE) - 0x200000)))
+
+# For development provide a target which makes barebox loadable by an
+# unmodified u-boot
+quiet_cmd_barebox_mkimage = MKIMAGE $@
+      cmd_barebox_mkimage = $(srctree)/scripts/mkimage -A $(ARCH) -T firmware -C none \
+       -O barebox -a $(UIMAGE_BASE) -e $(UIMAGE_BASE) \
+       -n "barebox $(KERNELRELEASE)" -d $< $@
+
+# barebox.uimage is build from the raw barebox binary, without any other
+# headers.
+barebox.uimage: $(KBUILD_BINARY) FORCE
+	$(call if_changed,barebox_mkimage)
+
 ifdef CONFIG_X86
 barebox.S: barebox
 ifdef CONFIG_X86_HDBOOT
@@ -1009,7 +1025,8 @@ CLEAN_FILES +=	barebox System.map include/generated/barebox_default_env.h \
                 .tmp_version .tmp_barebox* barebox.bin barebox.map barebox.S \
 		.tmp_kallsyms* barebox_default_env* barebox.ldr \
 		scripts/bareboxenv-target barebox-flash-image \
-		Doxyfile.version barebox.srec barebox.s5p
+		Doxyfile.version barebox.srec barebox.s5p barebox.ubl \
+		barebox.uimage
 
 # Directories & files removed with 'make mrproper'
 MRPROPER_DIRS  += include/config include2 usr/include